Frequently Asked Questions

The sections of the IBC and IRC that deal with sound transmission are IBC Section 1206 and IRC Appendix AK.  These code provisions apply to wall and floor/ceiling assemblies separating dwelling units from other dwelling units, or from adjacent public areas, within a building.  These provisions do not deal with sound transmission from outdoors to indoors, through an exterior wall.  Although US model building codes do not contain provisions regulating minimum sound transmission performance of exterior walls, there are some cases where designers specify a minimum level of sound transmission performance for exterior walls on specific construction projects.  In such cases, the most direct and accurate way of assessing sound transmission performance of an exterior wall is through field testing in accordance with ASTM E966 and analysis in accordance with ASTM E1332.  The single-number ratings resulting from this test and analysis procedure are outdoor-indoor transmission class (OITC) and outdoor-indoor noise isolation class (OINIC(θ)). Conversely, sound transmission class (STC) is determined through laboratory testing in accordance with ASTM E90 and analysis in accordance with ASTM E413.  This testing and analysis is most commonly used for assessing the sound transmission performance of interior walls and floor/ceiling assemblies separating dwelling units from other parts of a building, as these are the only places where US model building codes require minimum sound transmission performance.  While it is possible to perform an ASTM E90 test on an exterior wall assembly in a laboratory and determine an STC rating for that assembly using ASTM E413, this is less commonly done because building codes do not place minimum performance requirements on sound transmission through exterior wall assemblies and because OITC and OINIC(θ) ratings provide in-situ assessments of exterior wall performance.

As stated in Section 1.1 of ASTM E90, the scope of this standard is limited to building partitions such as walls, operable partitions, floor-ceiling assemblies, doors, windows, roofs, etc.  Although it is possible to use ASTM E90 to assess the sound transmission performance of individual components that would be used within an assembly, such use is not within the scope of the standard and is typically only done for the purpose of research.  Furthermore, sound transmission class (STC) values derived for individual components of an assembly are not necessarily additive.  In other words “component-additive methods” (CAM) do not necessarily yield accurate estimates of sound transmission through a complete assembly.  This is especially the case when dealing with assemblies that have a cavity or void through the thickness (e.g., a stud wall with cavities between the studs).  That said, there are other models (besides CAM) for estimating sound transmission performance that yield more accurate results.  For example, AWC’s Technical Report 15 (TR15) provides models that can be used to estimate STC and impact-insulation class (IIC) ratings for light-frame floor/ceiling assemblies (https://awc.org/publications/tr-15-calculation-of-sound-transmission-parameters-for-wood-framed-assemblies).

2012 International Residential Code (IRC) States:

R501.3 Fire protection of floors. Floor assemblies, not required elsewhere in this code to be fire resistance rated, shall be provided with a ½ inch gypsum wallboard membrane, 5/8 inch wood structural panel membrane, or equivalent on the underside of the floor framing member.

Exceptions:

1. Floor assemblies located directly over a space protected by an automatic sprinkler system in accordance with Section P2904, NFPA13D, or other approved equivalent sprinkler system. (AWC has developed a guide for partial sprinklering of unfinished basement areas.)
2. Floor assemblies located directly over a crawl space not intended for storage or fuel-fired appliances.
3. Portions of floor assemblies can be unprotected when complying with the following:3.1 The aggregate area of the unprotected portions shall not exceed 80 square feet per story.

   3.2 Fire blocking in accordance with Section R302.11.1 shall be installed along the perimeter of the unprotected portion to separate the unprotected portion from the remainder of the floor assembly.

4. Wood floor assemblies using dimension lumber or structural composite lumber equal to or greater than 2-inch by 10-inch nominal dimension, or other approved floor assemblies demonstrating equivalent fire performance.

The genesis for this requirement was five separate code change proposals introduced in 2009 to revise IRC. The IRC Code Development Committee disapproved all the proposals and requested that the interested parties work together to develop a public comment. In October 2010, the ICC membership approved the above text, jointly developed by the International Association of Fire Fighters, International Association of Fire Chiefs-Life Safety Section, the National Association of Home Builders, and the American Wood Council.

Q: Do I have to specially fire block the perimeter of the opening between the permitted 80 ft² unprotected area and the balance of the protected area?

A: Recent testing with an 80 ft² unprotected area has shown that if a fire occurred under a protected area, fire blocking would provide a minimal level of performance of the membrane system. This affirms the proponents’ intent that the perimeter between the 80 ft² unprotected area and the protected area needs to be fire blocked and no special treatment beyond the specified fire blocking is necessary to achieve the desired performance.

Q: Do I have to treat the joints in the gypsum wallboard with tape and compound?

A: Gypsum wallboard joints are not required to be finished with tape and joint compound. A somewhat analogous requirement in the code is a thermal barrier over foam plastic insulation. Such barriers are also not required to be finished with tape and joint compound. Likewise joints between wood structural panels are not required to be finished with wood filler and sanded.

Q: What was the intent when Clause R501.3, Exception 4 (R302.13 in the 2015 IRC) was developed?

A: As one of the original proponents of this language, AWC has insight into the intent and discussions leading to development of the wording in this exception.

To be considered equivalent to 2×10 sawn lumber or SCL, the framing members should support a load corresponding to 50% of the full bending design of the framing members, while being subjected to an ASTM E 119 time/temperature heating regime. All components utilized in the manufacture of the framing members (fasteners, plates, hardware, etc) should be utilized during testing. The test end criteria should be structural member failure.

AWC believes that the most straightforward and accurate means of determining the required minimum fire resistance time would be to estimate that time using the calculation methodology specified in NDS Chapter 16 for unprotected solid-sawn 2×10 floor joists assuming: a 3-sided exposure, a nominal char rate of 1.5 inches/hr, a bending strength to ASD ratio of 2.85, and supporting a load corresponding to 50% of full bending design.

A white paper entitled “Basis of IRC Membrane Protection Provisions” provides background and commentary on the IRC R501.3 provisions and the method used by the ICC Evaluation Service (ICC-ES) to establish equivalence and compliance with IRC R501.3, Exception 4.

See Chart in this PDF Document

The provisions for calculating bending deflection in the National Design Specification (NDS®) for Wood Construction Section 3.5 increase the long-term deflection with a creep factor, Kcr.  The creep factor ranges from 1.5-2.0. These NDS design provisions relate specifically to estimating total deflection including the effects of long-term loading.

The deflection limit for the D+L load combination only applies to the deflection due to the creep component of long-term (dead load) deflection plus the short-term (live load) deflection.  For wood structural members that are dry at time of installation and used under dry conditions, the creep component of the long-term deflection can be estimated as the immediate dead load deflection resulting from 0.5D.  For wood structural members at all other moisture conditions, the creep component of the long-term deflection is permitted to be estimated as the immediate dead load deflection resulting from D. These assumptions are consistent with the creep component of long-term deflection in NDS Section 3.5.

Deflection limits for the D+L load combination in IBC Table 1604.3 were taken from the legacy Uniform Building Code (UBC) deflection limits.  However, the intent of the UBC limits was not brought forward with the provisions.  The original intent of these provisions was to limit the total deflection based on the combination of live load deflection and the creep component of the dead load deflection.  As a result, there have been several prior code cycle modifications to these provisions to reinstate the original intent, such as the addition of Footnote G for steel structural members which effectively excludes steel from checking for the creep component of dead load deflection.  As currently written and formatted, the D+L deflection provision can be misinterpreted to suggest that the total deflection due to dead load, D, including both the immediate and creep components of the dead load deflection, should be used with the deflection limit in this column. Additionally, the use of 0.5D in Footnote D is potentially non-conservative without clarification that the 0.5D load reduction approach is only applicable to calculating the D+L deflection for use with the deflection limits in IBC Table 1604.3.  As a result, AWC has submitted a change to Table 1604.3 Footnote D to clarify these points and to make the 2015 IBC Table 1604.3 provisions consistent with the provisions in NDS 3.5.2 for long-term loading, with the stated intent in the UBC, and with similar provisions in ACI 318 as described in the ACI 318 Commentary.

We didn’t find any discussion in any of the codes we’ve referenced. Nothing either allowed or disallowed. The prevalence of surviving historical structures suggest these may be viable.

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The 2003 International Building Code (IBC) does not define seismic design coefficients for timber braced frames or three hinged arches. The only U.S. code source for this type of information is the 1997 Uniform Building Code (UBC). 1997 UBC Table 16-9 provides design coefficients for building frames and bearing wall systems. For braced frames in bearing wall systems (where frames are carrying gravity load as well as lateral load) reduced R factors are assigned. For heavy timber braced frames in 1997 UBC, R = 2.8 is assigned. For drift, Eq. 30-17 is applicable with the value of 0.7R being analogous to IBC’s Cd factor.

There are many applications for fire-retardant-treated wood (FRTW) in the International Building Code (IBC). The 2015 IBC defines FRTW in Chapter 2 as “Wood products that, when impregnated with chemicals by a pressure process or other means during manufacture, exhibit reduced surface-burning characteristics and resist propagation of fire.” Section 2303.2 sets the performance requirements for FRTW, including achieving a listed flame spread index of 25 or less, when tested to ASTM E84 or UL 723; no evidence of progressive combustion when the test is continued for an additional 20-minute period; and, the flame front not progressing more than 10.5 feet from the center of the burners at any time during the test.

Recently, there have been questions as to whether painted, coated, and other surface-treated wood products that may meet the flame spread testing criteria can be approved as FRTW, given the requirement for chemical impregnation of the wood. The short answer is that surface-coated wood products which do not have fire-retardant chemicals impregnated into the wood itself do not meet the strict IBC definition of FRTW, irrespective of meeting the flame spread requirements. However, surface-coated wood products can be approved for use in applications where FRTW is permitted, through the code’s alternative materials, design, and methods provisions found in Section 104.11, if appropriate testing and evaluation is conducted that establishes performance equivalency to FRTW.

What are these alternative provisions and on what basis can code officials approve surface-coated wood products? Section 104.11 of the IBC gives the code official authority to approve any alternative determined to be “satisfactory and complies with the intent of the code,” and is “not less than equivalent to what is prescribed in the code for quality, strength, effectiveness, fire resistance, durability, and safety.” One resource used by code officials to help in making this decision is the International Code Council Evaluation Services (ICC-ES), an independent subsidiary of ICC that provides technical evaluations of building products. ICC-ES relies on published acceptance criteria developed in open hearings and approved by the ICC-ES Evaluation Committee. This criteria provides a technical benchmark by which alternative products seeking to enter the marketplace may be evaluated. ICC-ES Acceptance Criteria is currently available for wood products with surface treatments intended to substitute for FRTW, including ICC-ES AC47, AC124, AC264, and AC479. These approved Acceptance Criteria require evaluation of surface burning characteristics of the product, durability and corrosivity of treatments, and effects of treatments on strength or stiffness of the wood substrate. Durability considerations, for example, help to ensure that the surface burning characteristics of the applied treatment remain effective after exposure to weather such as soak-freeze-thaw cycles or alternating UV/rain exposure. Code officials can use the resulting ICC-ES evaluation reports to approve and accept use of products in accordance with the conditions and requirements of the reports.

In the ICC code change cycle for the 2018 edition of the International Building Code (IBC), a clarification was approved for Section 2303.2.2. The intent of the code change is explained below by showing the change as originally proposed (S262-16) and the final approved change as modified by the committee.

Summary of Change to 2303.2.2 in 2018 Edition of IBC per S262-16

Change as originally proposed:

2303.2.2 Other means during manufacture. For wood products impregnated with chemicals by other means during manufacture, the treatment shall be an integral part of the manufacturing process of the wood product. The treatment shall provide permanent protection to all surfaces of the wood product. The use of paints, coatings, stains or other surface treatments shall not be permitted.

Final approved change as modified by the committee:

2303.2.2 Other means during manufacture. For wood products impregnated with chemicals by other means during manufacture, the treatment shall be an integral part of the manufacturing process of the wood product. The treatment shall provide permanent protection to all surfaces of the wood product. The use of paints, coatings, stains or other surface treatment are not an approved method of protection as required in this section.

Full committee reason in support of the final approved change as modified by the committee:

“This code change adds a necessary clarification to the use of surface treatments for wood. The modification makes the use of such materials possible as an alternate method.”

(S262-16 was approved as modified by the committee. For the ICC full documentation, see http://media.iccsafe.org/codes/2015-2017/GroupB/PCH/IBC-S.pdf and http://media.iccsafe.org/codes/2015-2017/GroupB/CAH/2016-Report-CAH.pdf.)

The approved modifications to 2303.2.2 clarify that the “other means during manufacture” subsection is not intended to permit surface-protected products as outright replacements for fire retardant treated wood (FRTW), given the requirement for chemical impregnation into the wood. The committee reason states: “This code change adds a necessary clarification to the use of surface treatments for wood.”

Importantly, though, the code development committee’s modifications to the original proposed change also preclude interpreting 2303.2.2 as an outright ban or prohibition on surface-coated products. The committee reason further states: “The modification makes the use of such materials possible as an alternate method.”

As has been the case for some time, wood products protected by surface treatments can be evaluated and approved by using the provisions of IBC 104.11 (See also Codes & Standards FAQ, “Can Surface-Coated Wood Products be Approved for Use in Applications Where Fire-Retardant-Treated Wood is Permitted?”).

Full Question:

What is the background behind footnote “m” of IBC 2012 table 721.1 (2) which states:

“^m For studs with a slenderness ratio, le/d, greater than 33, the design stress shall be reduced to 78 percent of allowable F′c. For studs with a slenderness ratio, le/d, not exceeding 33, the design stress shall be reduced to 78 percent of the adjusted stress F′c calculated for studs having a slenderness ratio le/d of 33.”

Answer:

Most North American fire tests on wood stud wall assemblies were conducted between 1950 and 1975.  During that time, the standard wall configuration was a 10 foot x 10 foot wall using 2×4 Select Structural grade Douglas Fir-Larch or 2×4 #1 Dense grade Southern Pine studs.  These grades were chosen to allow a single, highly-loaded test to be used for all lower grade studs.

In 1982, the design values for compression perpendicular-to-grain stress (F_c-perp) were increased due to changes made to ASTM D245 Standard Practice for Establishing Structural Grades and Related Allowable Properties for Visually Graded Lumber.  D245 provisions were changed so that reference F_c-perp design values were derived from F_c-perp test results at 0.04″ deformation rather than at proportional limit which had previously been used.  Because of this change, designs which had previously been limited by F_c-perp, such as bearing wall assemblies, were then limited by other criteria.

The National Forest Products Association (NFPA) staff was asked if the wall assembly fire resistance tests conducted between 1950 and 1975 were valid since the loads on the walls were now often limited by the calculated buckling stress, F_cE, rather than the calculated bearing.  Recognizing that the fire resistance of an assembly under a given load would not change just because the reference basis of the design value had been changed, the maximum calculated load capacity of the assembly using the old and new criteria were calculated and compared based on the 1982 design values for F_c-perp.

Using the F_c-perp design values which have been in place since 1982, the calculated load capacity of 2×4 wall assemblies are typically limited by column buckling in the strong axis direction.  Several design assumptions were resolved for the final comparison.  First, the actual stud length for a 10 foot wall was assumed to be 115.5 inches (120-3*1.5).  Also, since it was unclear which grades of lumber were used in the fire tests, staff compared Select Structural, #1, #2 and #3 grades and found that the most conservative assumption was to use design values for Select Structural for the comparisons.

Most wall assembly tests that are the basis of the 1 and 2-hour wood wall assemblies in the International Building Code (IBC) were 10′ walls using 2×4 studs.  From the above calculation, it was valid (though conservative) to limit the capacity of those wall assemblies to 78% of the adjusted allowable compression design value at a L_e/d ratio of 33.  Since 1999, AWC has conducted multiple wall assembly tests that permit the use of 2×4 and 2×6 wall assemblies at full design load (100% of designs per the 2005 National Design Specification (NDS) and later versions). These assemblies have been included in the IBC and are described in DCA3.

Among the changes approved in the current code change cycle was G109-18, which will, for the first time, allow concealed spaces in traditional Type IV heavy timber buildings. The concealed spaces must be protected with one or more of the following three alternatives:

• the building is sprinklered throughout and sprinkler protection is provided in the concealed space,
• surfaces in the concealed space are fully sheathed with 5/8-inch Type X gypsum board, or
• the concealed space is filled completely with noncombustible insulation.

There is an exception for stud spaces in framed one-hour interior walls and partitions, which are permitted in Type IV-HT construction.

These same provisions have often been accepted by code officials through alternate methods as necessary protection for concealed spaces in traditional Type IV construction. The 2021 edition of the IBC will have a code path for acceptance without resorting to the alternative methods and materials section of the code. This should greatly help in the rehabilitation of many existing heavy timber buildings that are being put back into use as new occupancies and will allow new construction of Type IV-HT with concealed spaces that are commonly found in residential occupancy groups where ceilings may conceal overhead plumbing and mechanicals.

The 2021 International Building Code will require a Site Safety Director, employed by the building owner, to conduct and document daily construction fire safety inspections. This is only one of several new requirements approved in F263-18 and F264-18 for buildings under construction. According to the new requirements, the fire official is authorized to issue a stop work order upon repeated omissions in inspection and/or documentation of the following:

• the training qualifications of hot work contractors admitted to the site (must have received training in the hot work safety requirements of IFC Chapter 35)
• observing that hot work is performed only in pre-approved locations
• safety of temporary heating equipment
• removal of trash and debris
• safety of temporary wiring
• safe storage of flammable liquids and hazardous materials
• openness of fire access roads
• fire hydrant visibility and access
• availability of operating standpipes as construction progresses
• fire extinguisher placement

The National Fire Protection Association reports that for a five-year period from 2010 through 2014, fires at sites undergoing construction, major renovation, and demolition averaged 17% of annual fire department structure fire responses and 3.2% of annual fire losses in the U.S. For more information see https://constructionfiresafety.org/.

Footnote “c” of IBC Table 601 permits heavy timber for roof construction in all construction types except Type I-A when the required fire resistance is one hour or less. But what if a roof member is also part of the primary structural frame of the building, which is governed by a separate row of Table 601? A code change was approved in the last ICC code change cycle, G102-18, which makes it clear that footnote “c” applies even if the roof member is a part of the primary structural frame. The footnote in the 2021 IBC will read “In all occupancies, heavy timber complying with Section 2304.11 shall be allowed for roof construction, including primary structural frame members, where a 1-hour or less fire-resistance rating is required.”

Code provisions on this point have flip-flopped in recent years. The 2012 IBC limited projections to no less than 2 feet from the property line if the fire separation distance (FSD, usually the distance from the exterior wall to the property line) was less than 5 feet, or no less than 40 inches to the property line when the fire separation distance was 5 feet or greater. The 2015 IBC took a detour and set the minimum projection distance at “24 inches plus 8 inches for every foot of FSD beyond 3 feet or fraction thereof” beginning at an FSD of 3 feet, which resulted in much greater restrictions. Then, the 2018 IBC dropped this formula and went back to the 40-inch limit when the building had an FSD of at least 5 feet but kept the formula for buildings with an FSD between 3 feet and less than 5 feet. And most recently, a 2021 IBC change will strike the “old” formula for buildings with an FSD from 3 to less than 5 feet and will replace it with “2/3 the FSD” (see ICC code change FS14-18).

Bottom line? The 2021 IBC will be only slightly more restrictive on the proximity of commercial building projections to the property line than the 2012 IBC, and only for buildings with an FSD from 3 to less than 5 feet. Keep in mind that combustible projections extending to within 5 feet of the property line must be of 1-hour construction, heavy timber, or fire-retardant-treated wood. There’s an exception to this for Type V-B construction with an FSD of at least 5 feet (see 705.2.3 of the 2018 IBC).

Section 704.2 of the 2018 International Building Code (IBC) was revised from its origin which began in the legacy building codes and was primarily intended to address steel construction. In earlier editions of the IBC, omission of fireproofing on portions of steel columns or beams behind ceiling or wall membranes of fire-resistance-rated assemblies was permitted. During more recent code development cycles, it was agreed that membrane protection alone was inadequate, especially for members carrying the upper floors of a building, since they could be exposed to fire which originates in a concealed space or from fire in a room if the membrane protection fails. Because steel has no inherent fire resistance (steel can yield quickly at temperatures commonly occurring in fires), the method and location of the protection is considered critical.

The 2018 IBC was revised to clearly indicate that columns as well as studs and boundary elements in walls of light-frame construction and are located entirely between the top and bottom plates are permitted to have their required fire resistance ratings provided by the membrane protection for the wall. Elements within fire-resistance-rated walls of light-frame construction are addressed directly in IBC Section 704.4.1 (Light-frame Construction) and can be part of a fire-resistance-rated wall assembly without any additional fire protection. Many buildings are built out of typical light frame construction; the concentrated loads from trusses or beams must have a continuous load path to the foundation. Previously, some jurisdictions were interpreting that these construction elements were considered primary structural columns and requiring them to be provided with individual fire protection. It was never the intent to require individual fire protection of these elements as they are not considered a portion of the primary structural frame.

IBC Section 202 defines the Primary Structural Frame as the Columns; Structural Members, Floor Construction and Roof Construction (all having direct connections to the columns); and Bracing members essential to the vertical stability of the primary structural frame under gravity loading. IBC Section 704.2 requires all columns, that are required to be protected, to be protected with individual encasement protection throughout the entire column length. This section clarifies that columns extending up through the ceiling must extend the required encasement protection from the foundation to the beam above.

By definition, a light-frame construction wall is primarily built with repetitive studs. When braced by sheathing or gypsum board attached to the wall framing, the design of studs, multiple studs, or posts is similar based on the L/d for the member buckling out of the plane of the wall. Perpendicular to grain bearing of the studs on the top and bottom plates is also a consideration and is the same regardless of whether the studs are spaced, studpacks, or posts. The structural design of all of these members is considered column design. In previous editions of the IBC or legacy codes an issue sometimes occurred when studs, multiple studs, or solid sawn members were framed integrally within a fire-resistance-rated light frame wall and were treated as columns according to the definition of primary structural frame, and were then required to be provided with individual encasement protection.

The intent of Sections 704.2 and 704.4.1 have been clarified in the 2018 IBC to state studs, boundary elements, posts, multiple stud groups, built-up columns, and solid columns that are framed within the wall and do not penetrate the top or bottom plates are all designed to the same criteria and shall be considered integral elements. These elements that are integral within the confines of the load bearing wall, and do not penetrate the top or bottom plates, are permitted to be protected in light frame construction by the membrane protection of the fire-resistance-rated bearing wall.

What is the correct application of 2018 IBC Section 704.3 (Protection of the primary structural frame other than columns) to wood construction?

Definitions for “primary structural frame” and “light-frame construction” are included in IBC Chapter 2. IBC Section 704.3 (Protection of the primary structural frame other than columns) is for systems that meet the definition of “primary structural frame,” but not heavy timber or light-frame construction. Floor joists, ceiling joists, and rafters in light-frame construction do not fall within the definition of primary structural frame. Likewise, wood beams, if required to be rated, (Type IIIA or VA building) are typically part of a light-frame system. Their fire resistance would be established by normal means, whether calculating fire resistance as an exposed wood member or protecting with other materials. As for Type IV, Table 601 requires no fire resistance rating for structural elements, as long as they meet the minimum required dimensions for Type IV construction as specified in IBC Section 2304.11.sf.

The provisions of NDS Chapter 16 and FDS Chapter 3 are intended to allow the designer to use analytical methods to establish the fire resistance time associated with a wood member or assembly tested to an ASTM E119 fire exposure. In this mechanics-based design method, wood design properties intended for structural design are adjusted to nominal strengths for fire resistance calculations. These nominal strengths are used with cross-sections, reduced due to charring of the wood, to calculate the time to structural failure of a wood member or assembly. As such, application of the slenderness limits intended to provide safe structural designs to provisions for estimating structural failure time is unnecessary and would reduce accuracy of the estimated failure time. Reference to the equation 3.7-1 is provided within Chapter 16 to remind the user that the stability equations should be applied in the design of columns. Reference to the stability equations like 3.7-1 were only to remind the user that stability equations should be applied, but not intended to require application of design slenderness ratio limitations that are specific to structural design.  As stated in NDS Commentary Section C16.1, these provisions do not address procedures for evaluating members for continued service following fire damage.

Warnock Hersey published a report on a 1-hour fire test. For more information, contact Warnock Hersey at (608) 836-4400.

For any additional help, ​contact ​AWC.

Fire retardant treatments (FRT) on wood products retard the ability of flames to spread across the surface of wood products. However, fire retardants do not reduce the rate at which wood degrades when subjected to an external heat source. Accordingly, fire retardant treatments do not improve fire resistance ratings to any significant extent. The user is reminded that NDS 2.3.4 requires the effects of fire retardant chemical treatment on strength to be addressed in design.

Does fire retardant treatment (FRT) make wood non-combustible?

FRT wood does not meet the requirements for noncombustible materials. However, in recognition of its very low flamespread characteristic, the International Building Code (IBC) allows FRT wood to be used in many applications otherwise required to be of non-combustible construction. See the construction type definitions in Chapter 6 of the code, and also Section 603 which lists many applications for FRT wood in noncombustible construction types.

See also the Fire FAQ: “Where can I find publications on fire retardant treated wood?”

The 2012 IBC Section 2303.1.1.2 states: Approved end-jointed lumber is permitted to be used interchangeably with solid-sawn members of the same species and grade. End-jointed lumber used in an assembly required to have a fire-resistance-rating shall have the designation “Heat Resistant Adhesive” or “HRA” included in its grade mark. In 2009 the American Lumber Standards Committee (ALSC) modified the ALSC Glued Lumber Policy to add elevated-temperature performance requirements for end-jointed lumber adhesives intended for use in fire-resistance-rated assemblies. End-jointed lumber manufactured with adhesives which meet the new requirements is being designated as “Heat Resistant Adhesive” or “HRA” on the grade stamp.

The ALSC Glued Lumber Policy requires that Heat Resistant Adhesives be qualified in accordance with one of two new ASTM standards, D7374-08 Practice for Evaluating Elevated Temperature Performance of Adhesives Used in End-Jointed Lumber and D7470-08 Practice for Evaluating Elevated Temperature Performance of End-Jointed Lumber Studs. Both standards require a wall assembly made with end-jointed lumber to be subjected to the ASTM E119 fire test. The tested-adhesive qualifies as a Heat Resistant Adhesive if the wall assembly achieves a one-hour fire-resistance-rating. End-jointed lumber manufactured with a Heat Resistant Adhesive under an auditing program of an ALSC-accredited grading agency is allowed to carry the HRA mark on the grade-stamp. End-jointed lumber manufactured with an adhesive not qualified as a Heat Resistant Adhesive will be designated as “Non-Heat Resistant Adhesive” or “non-HRA” on the grade stamp. Lumber carrying the HRA mark is permitted to be used interchangeably with solid-sawn members of the same species and grade in fire-resistance-rated applications.

For more information, please contact AWC at 202-463-4713 or [email protected].

A legacy publication titled Design of Firestopping and Draftstopping for Concealed Spaces provides recommendations on where and how fire/draftstopping should be used to prevent spread of fire by restricting movement of flame, air, gasses, and smoke in buildings. 16 pages. (T45) Available from the AWC Helpdesk upon request: [email protected].

Visit http://www.fpl.fs.fed.us/

Columns and beams in Type IV-HT construction are not required to be fire-resistance rated by IBC Table 601, which only requires them to be of “HT” (heavy timber) dimensions, which are found in Table 2304.11. Connections of heavy timber members that are not fire resistance rated are not required to be protected. However, for heavy timber members in any type of construction that are required to be fire-resistance rated by other provisions of the code (for instance, a column or beam that supports a required fire-resistance rated floor), Section 704 of the IBC requires their connections to other structural members to be protected for least the fire-resistance rating of the connected members. Chapter 16 of the NDS, which is referenced in Section 722 of the IBC, requires this protection to be provided by wood cover, fire-rated gypsum board, or other approved material.

Details for exterior wall/floor intersections in Type III construction are included in Design for Code Acceptance No. 3 Fire Resistance Rated Wood Frame Wall and Floor Assemblies (AWC DCA-3). The details may be helpful when a one-hour floor ceiling assembly intersects with a two-hour exterior wall in traditional platform construction, if there are concerns about the continuity of the exterior wall rating. The details are accompanied by text which explains the methodology for maintaining the fire resistance of both assemblies.

ICC Evaluation Services Acceptance Criteria 479 Wood Structural Panels with a Factory-Applied Fire-Retardant Coating was expanded in scope in 2018 to include sawn lumber. AWC anticipates that multiple manufacturers of liquid-applied fire retardants intended for use with wood products will seek alternate materials and methods approvals for sawn lumber applications of their products. Additionally, multi-family builders may choose to use new fire retardant products on sawn lumber as a construction fire prevention measure.

Among the changes approved in the current code change cycle was G109-18, which will, for the first time, allow concealed spaces in traditional Type IV heavy timber buildings. The concealed spaces must be protected with one or more of the following three alternatives:

• the building is sprinklered throughout and sprinkler protection is provided in the concealed space,
• surfaces in the concealed space are fully sheathed with 5/8-inch Type X gypsum board, or
• the concealed space is filled completely with noncombustible insulation.

There is an exception for stud spaces in framed one-hour interior walls and partitions, which are permitted in Type IV-HT construction.

These same provisions have often been accepted by code officials through alternate methods as necessary protection for concealed spaces in traditional Type IV construction. The 2021 edition of the IBC will have a code path for acceptance without resorting to the alternative methods and materials section of the code. This should greatly help in the rehabilitation of many existing heavy timber buildings that are being put back into use as new occupancies and will allow new construction of Type IV-HT with concealed spaces that are commonly found in residential occupancy groups where ceilings may conceal overhead plumbing and mechanicals.

The 2021 International Building Code will require a Site Safety Director, employed by the building owner, to conduct and document daily construction fire safety inspections. This is only one of several new requirements approved in F263-18 and F264-18 for buildings under construction. According to the new requirements, the fire official is authorized to issue a stop work order upon repeated omissions in inspection and/or documentation of the following:

• the training qualifications of hot work contractors admitted to the site (must have received training in the hot work safety requirements of IFC Chapter 35)
• observing that hot work is performed only in pre-approved locations
• safety of temporary heating equipment
• removal of trash and debris
• safety of temporary wiring
• safe storage of flammable liquids and hazardous materials
• openness of fire access roads
• fire hydrant visibility and access
• availability of operating standpipes as construction progresses
• fire extinguisher placement

The National Fire Protection Association reports that for a five-year period from 2010 through 2014, fires at sites undergoing construction, major renovation, and demolition averaged 17% of annual fire department structure fire responses and 3.2% of annual fire losses in the U.S. For more information see https://constructionfiresafety.org/.

Attic fires can be a significant hazard in residential mid-rise structures. The 2018 IBC has provisions for increased attic protection based on the height of the building. For wood construction, when the roof assembly exceeds 55 feet above the lowest level of required fire department vehicle access, the attic must be protected by sprinklers or alternative protection must be provided. This means that certain special occupancy “pedestal” buildings must have sprinkler-protected attics even if they could have an NFPA 13R sprinkler system (as opposed to a full NFPA 13 system). See subsection 903.3.1.2.3 Attics in the 2018 IBC for the full requirements.

A reminder: sprinklers do no good if a fire begins before sprinklers are operational. See the Construction Fire Safety Coalition website for resources on preventing construction fires: www.constructionfiresafety.org

Section 704.2 of the 2018 International Building Code (IBC) was revised from its origin which began in the legacy building codes and was primarily intended to address steel construction. In earlier editions of the IBC, omission of fireproofing on portions of steel columns or beams behind ceiling or wall membranes of fire-resistance-rated assemblies was permitted. During more recent code development cycles, it was agreed that membrane protection alone was inadequate, especially for members carrying the upper floors of a building, since they could be exposed to fire which originates in a concealed space or from fire in a room if the membrane protection fails. Because steel has no inherent fire resistance (steel can yield quickly at temperatures commonly occurring in fires), the method and location of the protection is considered critical.

The 2018 IBC was revised to clearly indicate that columns as well as studs and boundary elements in walls of light-frame construction and are located entirely between the top and bottom plates are permitted to have their required fire resistance ratings provided by the membrane protection for the wall. Elements within fire-resistance-rated walls of light-frame construction are addressed directly in IBC Section 704.4.1 (Light-frame Construction) and can be part of a fire-resistance-rated wall assembly without any additional fire protection. Many buildings are built out of typical light frame construction; the concentrated loads from trusses or beams must have a continuous load path to the foundation. Previously, some jurisdictions were interpreting that these construction elements were considered primary structural columns and requiring them to be provided with individual fire protection. It was never the intent to require individual fire protection of these elements as they are not considered a portion of the primary structural frame.

IBC Section 202 defines the Primary Structural Frame as the Columns; Structural Members, Floor Construction and Roof Construction (all having direct connections to the columns); and Bracing members essential to the vertical stability of the primary structural frame under gravity loading. IBC Section 704.2 requires all columns, that are required to be protected, to be protected with individual encasement protection throughout the entire column length. This section clarifies that columns extending up through the ceiling must extend the required encasement protection from the foundation to the beam above.

By definition, a light-frame construction wall is primarily built with repetitive studs. When braced by sheathing or gypsum board attached to the wall framing, the design of studs, multiple studs, or posts is similar based on the L/d for the member buckling out of the plane of the wall. Perpendicular to grain bearing of the studs on the top and bottom plates is also a consideration and is the same regardless of whether the studs are spaced, studpacks, or posts. The structural design of all of these members is considered column design. In previous editions of the IBC or legacy codes an issue sometimes occurred when studs, multiple studs, or solid sawn members were framed integrally within a fire-resistance-rated light frame wall and were treated as columns according to the definition of primary structural frame, and were then required to be provided with individual encasement protection.

The intent of Sections 704.2 and 704.4.1 have been clarified in the 2018 IBC to state studs, boundary elements, posts, multiple stud groups, built-up columns, and solid columns that are framed within the wall and do not penetrate the top or bottom plates are all designed to the same criteria and shall be considered integral elements. These elements that are integral within the confines of the load bearing wall, and do not penetrate the top or bottom plates, are permitted to be protected in light frame construction by the membrane protection of the fire-resistance-rated bearing wall.

What is the correct application of 2018 IBC Section 704.3 (Protection of the primary structural frame other than columns) to wood construction?
Definitions for “primary structural frame” and “light-frame construction” are included in IBC Chapter 2. IBC Section 704.3 (Protection of the primary structural frame other than columns) is for systems that meet the definition of “primary structural frame,” but not heavy timber or light-frame construction. Floor joists, ceiling joists, and rafters in light-frame construction do not fall within the definition of primary structural frame. Likewise, wood beams, if required to be rated, (Type IIIA or VA building) are typically part of a light-frame system. Their fire resistance would be established by normal means, whether calculating fire resistance as an exposed wood member or protecting with other materials. As for Type IV, Table 601 requires no fire resistance rating for structural elements, as long as they meet the minimum required dimensions for Type IV construction as specified in IBC Section 2304.11.sf.

There are no specific code requirements or allowances in the IBC for determining the fire resistance of a connection itself. In fact, there are no code-prescribed means of establishing the fire resistance of a connection by itself. The standard fire-resistance tests referenced in the IBC (ASTM E119 and UL 263) do not provide the necessary protocol for testing a connection configuration in the furnace. However, the IBC does require fire protection of connections, and this protection must consist of materials that provide a fire-resistance rating not less than that required of the connected members. Specifically, IBC Sections 704.2 and 704.3 make explicit reference to the requirement for fire protection of connections as follows:

704.2 Column protection. Where columns are required to have protection to achieve a fire-resistance rating, the entire column shall be provided individual encasement protection by protecting it on all sides for the full column height, including connections to other structural members, with materials having the required fire-resistance rating. Where the column extends through a ceiling, the encasement protection shall be continuous from the top of the foundation or floor/ceiling assembly below through the ceiling space to the top of the column.

704.3 Protection of the primary structural frame other than columns. Members of the primary structural frame other than columns that are required to have protection to achieve a fire-resistance rating and support more than two floors or one floor and roof, or support a load-bearing wall or a nonload-bearing wall more than two stories high, shall be provided individual encasement protection by protecting them on all sides for the full length, including connections to other structural members, with materials having the required fire-resistance rating.

It should be noted that these code sections are not specific to any particular construction type or construction material; so they apply to connections in steel construction, concrete construction, and the new mass timber construction types alike. That said, most of the members in traditional heavy timber construction (now called Type IV-HT) are not required to meet an explicit fire resistance rating, so the connections between these members are not necessarily required to be protected.

For connections between structural members in the new mass timber construction types (Types IV-A, IV-B and IV-C), the protection time provided by the fire protection to be applied over the connection must be determined based on a standard fire exposure. Section 703.3 provides the various methods that are permitted for establishing the fire-resistance rating of building elements, component or assemblies based on a standard fire exposure. These are as follows:

• Fire-resistance designs documented in approved sources.
• Prescriptive designs of fire-resistance-rated building elements, components or assemblies as prescribed in Section 721.
• Calculations in accordance with Section 722.
• Engineering analysis based on a comparison of building element, component or assemblies designs having fire-resistance ratings as determined by the test procedures set forth in ASTM E119 or UL 263.
• Alternative protection methods as allowed by Section 104.11.
• Fire-resistance designs certified by an approved agency.
• The procedure for protecting connections provided in AWC Technical Report No. 10 (TR10) is based on the results of ASTM E119 tests, particularly as it pertains to the char rate of wood and/or the performance of gypsum wallboard. Thus, these TR10 provisions for protecting connections with wood and/or gypsum wallboard provide a means of determining fire resistance that is in compliance with item 4 of IBC Section 703.3.

The video was published in 1993 by Odyssey Productions, Inc. and was sponsored by WWPA, AF&PA, SFPA, and APA. Contact SFPA (Southern Forest Products Association) at 504-443-4464 or http://www.sfpa.org. Ref #AV45

1. International Codes Council
   ICC Consensus Committee on Log Structures (IS-LOG): Information on the development of the ICC Standard on Design, Construction and Performance of Log Structures (ICC-400).
   • ICC Headquarters
     • 5203 Leesburg Pike
       Suite 600, Falls Church, VA 22041
   • Phone: (888) ICC-SAFE (422-7233)
   • Fax: (703) 379-1546
   • Website: http://www.iccsafe.org/
2. Log Homes Council (National Association of Home Builders)
   • 1201 15th Street
     Washington, D.C 20005
   • Phone: (800) 368-5242, ext. 8576
   • Fax: (202) 266-8141
   • Email: [email protected]
   • Website: http://www.loghomes.org
   • All Log Home Council members must participate in a monitored Log Grading Program. Their technical consultant is:
3. Mr. Rob Pickett
   • Rob Pickett & Associates
   • PO Box 490
     Hartland, VT 05048-0490
   • Phone: (802) 436-1325
   • Fax: (803) 436-1325
   • Email: [email protected]
   • Website: http://robpickettandassoc.com/
4. Visual Stress Grading of Wall Logs and Sawn Round Timbers Used in Log Structures, by Edwin J. Burke, Ph.D., Univ. of Montana, Wood Design Focus, Vol. 14, No. 1. Abstract: This article explains the need for and the history and process of stress grading logs used in construction of log structures and offers practical information for engineers, architects, and code officials working with this type of construction system. For ordering information, visit http://www.forestprod.org/
5. Dr. Edwin J. Burke
   • Professor of Wood Science
     University of Montana
     School of Forestry; Wood Science Associates
   • 2617 Garland Drive
     Missoula, MT 59803
   • Phone: (406) 251-4325
   • Fax: (406) 251-6189
   • Email: [email protected]
6. ASTM D3957 – 09(2015) Standard Practices for Establishing Stress Grades for Structural Members Used in Log Buildings defines two types of structural members used in log buildings; Wall-Logs and Sawn Round Timber Beams. For more information, visit http://www.astm.org/

AWC Wood Frame Construction Manual (WFCM) 2015 Edition is presently referenced in model building codes such as the IBC (International Building Code) and IRC (International Residential Code). The WFCM is an ANSI-approved document that provides engineered and prescriptive requirements for wood frame construction based on dead, live, snow, seismic, and wind loads from ASCE 7-10 Minimum Design Loads for Buildings and Other Structures.

AWC Special Design Provisions for Wind and Seismic (SDPWS) 2015 Edition is presently referenced in model building codes such as the IBC. The SDPWS is an ANSI-approved document that covers materials, design, and construction of wood members, fasteners, and assemblies to resist wind and seismic forces.

Wood has a high strength-to-weight ratio. Since wood is lighter than steel or concrete, there is less mass to move—a critical factor during an earthquake. Wood members connected with steel fasteners create a very ductile (flexible) assembly which is less prone to brittle failures often seen with unreinforced masonry or concrete structures.

Multiple, repetitive wood members (studs, joists, and rafters at 16”-24” on-center) provide redundancy in wood assemblies making them less prone to catastrophic collapse. Wood’s renewability, low life-cycle environmental impacts, and ability to sequester carbon provides the optimal combination of green building and stability for earthquake-prone areas.

Tests have proven the viability of wood frame structures under seismic loads.

Here are some resources for this issue:

1. General information is available in the ASD/LRFD Manual. The longitudinal direction shrinkage (from green to oven dry) for normal wood usually ranges from 0.1 to 0.2 percent of the green dimension. For the radial and tangential directions, there is an approximate 1% change in dimensions per 4% change in moisture content.
2. USDA Wood Handbook Chapter 4.
3. WWPA Shrinkage Tech
4. Canadian Wood Council’s “DimensionCalc” will calculate for the dimensional change in wood due to shrinkage

For information on timber bridge design and construction, contact one of the following organizations:

1. Forest Products Laboratory’s Timber Bridge Design Manual. (608) 231-9200. For more information, visit http://www.fpl.fs.fed.us
2. American Institute of Timber Construction’s revised Timber Bridge brochure. Visit their website at http://www.aitc-glulam.org
3. National Wood in Transportation Information Center
   USDA Forest Service
   180 Canfield Street
   Morgantown, WV 26505
   Phone: (304) 285-1591
   Fax: (304) 285-1596
   Email: [email protected]
   Website: http://www.na.fs.fed.us/werc/

A typical timber frame structure utilizes posts and beams, shaped at their connections to lock together. Modern timber frame work is generally exposed.

Find information from Volume 14, Number 3 of Wood Design Focus.

Also see the Timber Framers Guild.

Contact APA – the Engineered Wood Association for additional assistance. AITC’s Timber Construction Manual contains information on bowstring trusses.

Method Increased Buckling Capacity of Built-Up Beams and Columns by Donald A. Bender, Robert E. Kimble, and Frank E. Woeste appeared in the 2010 Winter (Vol.20, No. 4) issue of Wood Design Focus.

Stability of Built-Up Timber Beams and Columns: Accounting for Modulus of Elasticity Variability by Robert E. Kimble, P.E. and Donald A. Bender, P.E. appeared in ASCE’s Practice Periodical on Structural Design and Construction, Vol. 15, No. 4, November 1, 2010.

Calculating buckling capacity of built-up beams and columns by Donald A. Bender, PE; Robert E. Kimble, PE; Frank E. Woeste, PE.

The National Association of Home Builders (NAHB) publishes a publication titled Residential Construction Performance Guidelines, which has information on construction tolerances. There are versions for both homeowners and contractors. Visit http://www.builderbooks.com/ for ordering information.

National Association of Home Builders
1201 15th Street, NW
Washington, DC 20005

Phone: (202) 266-8200
Toll-Free: (800) 368-5242
Fax: (202) 266-8400

In addition, WoodWorks offers information on Common Construction Tolerance Limits for Light-frame Wood Construction.

Fastener Corrosion

Background

Starting January 1, 2004, Chromated Copper Arsenate (CCA) treated wood products were no longer permitted to be manufactured for general sale, with only some minor exceptions for use in limited, well-defined applications. (See https://www.epa.gov/ingredients-used-pesticide-products/chromated-arsenicals-cca
for more information.). Some of the commonly available preservative-treated wood products will be treated with ammoniacal copper quat (ACQ), copper azole (CBA/CA-B), or ammoniacal copper zinc arsenate (ACZA). While these alternative treating chemicals have been proven to be effective wood preservatives when used in accordance with AWPA standards, there is some evidence that these chemicals are more corrosive than CCA to metal fasteners and connectors.

The purpose of this document is to provide answers to some specific questions related to this issue. Users are cautioned that this information is only a synthesis of reports currently available from public sources. A number of sources are attempting to assess the corrosivity of treatment chemicals. Updates will be issued as new or additional information becomes available.

Questions and Answers

Q: Lumber treated with CCA has been available for many years. Does metal corrode in contact with CCA-treated lumber?

The chemicals used in CCA-treated lumber have been shown to be somewhat corrosive to fasteners and connectors. Accordingly, chemical manufacturers and the treated lumber industry have traditionally recommended and the model building codes have required the use of corrosion-resistant fasteners and connectors when used with CCA-treated lumber.

Q: What’s different with the new alternative treatments?

When subjected to standardized laboratory tests that accelerate the corrosion process, metal connectors and fasteners exposed to the chemicals used in ACQ, Copper Azole, or ACZA exhibit higher rates of corrosion than connectors and fasteners exposed to CCA. Discussions within the affected industries are attempting to sort out the significance of these differences in real-world applications.

Q: What should users do while the technical issues are being evaluated?

At the very least, users should rigorously apply the recommendations of the chemical manufacturers and the treating industry—to use corrosion-resistant fasteners and connectors or zinccoated (galvanized) fasteners and connectors with corrosion protection at least equivalent to that of hot-dip galvanized products.

Q: What zinc coating specifications apply to hot-dip galvanized products used in wood building construction?

Specifications for sheet metal connectors (joist hangers and metal straps) and fasteners (such as nails and bolts) are addressed in separate ASTM standards. Coating weight designations for sheet steel are specified in ASTM A 653, Standard Specification for Steel Sheet, Zinc-Coated (Galvanized) or Zinc-Iron Alloy-Coated (Galvannealed) by the Hot-Dip Process. An example zinc coating designation in ASTM A 653 is G185 where “G” indicates zinc coating and “185” indicates a total of 1.85 oz/ft² of coating on both sides of the steel sheet. For fasteners, minimum coating weights are specified in ASTM A 153, Standard Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware. A Class D designation applies for fasteners 3/8” in diameter and smaller. The minimum coating weight associated with Class D is 1.0 oz/ft².

Q: Is there a difference between “hot-dip” galvanized products and other types of galvanized products manufactured using a different process?

There are a variety of processes for galvanizing metal products other than the hot-dip process. These include electrolysis (electrogalvanized, zinc plated) and peening (mechanical plating). There are some differences and issues that users should be aware of:

Coating thicknesses developed by the electrolysis process may be too thin. Most commonly available electrogalvanized or zinc-plated fasteners and connectors do not have a sufficient coating of zinc for these new chemicals.

The density of the coating can be less than provided by the hot-dip process. For example, mechanically deposited coating in accordance with ASTM B 695 Standard Specification for Coatings of Zinc Mechanically Deposited on Iron and Steel has a density that is approximately 75% of the density of the zinc coating resulting from the hot-dip process. Approximately 33% greater coating thickness is needed to produce the same level of zinc per unit area as provided by the hot-dip process.

Q: What connectors provide maximum corrosion resistance?

Type 304 and 316 stainless steel have been used to provide maximum corrosion resistance. Type 304 and 316 stainless steel connectors and fasteners have been used in demanding applications such as coastal exposures and in permanent wood foundations.

Q: What other details should users and specifiers be aware of?

There are other issues that have been reported that are important to users:

Never mix galvanized steel with stainless steel in the same connection. When these dissimilar metals are in physical contact with each other, galvanic action will increase the corrosion rate of the galvanized part (the zinc will migrate off the galvanized part onto the stainless part at a faster rate).

Galvanizing provides a sacrificial layer to protect the steel connector or fastener. Greater thicknesses (coating weights—see Table 1) generally provide longer protection in corrosive environments.

Aluminum should not be used in direct contact with CCA, ACQ, Copper Azole, or ACZA.

Q: Are all alternative treatments more corrosive than CCA?

The majority of the research has been conducted on the corrosivity of ACQ and Copper Azole. Comparative testing has indicated that borates are less corrosive but users should still consult manufacturer recommendations regarding corrosion-resistant fasteners or corrosion protection of fasteners and suitable applications for borate treatments.

More Information

A search on the internet will provide a long list of “hits” on this topic. Information on the following web sites may be especially useful to users of treated wood products:

General:

The Federal Emergency Management Agency (FEMA) provides recommendations for fasteners and connectors used in coastal areas – Technical Bulletin 8-96 Corrosion Protection for Metal Connectors in Coastal Areas.

The American Galvanizers Association (AGA) provides information types of zinc coatings and characteristics of zinc coatings – Zinc Coating

Additional Resources and Information is Available From: 

• Viance Treated Wood Solutions
• Osmose, Inc.

Schein, E.W. 1968. The Influence of design on exposed wood in buildings of the Puget Sound area. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 41 p.

Part A (PDF 2.77 Mb)
Part B (PDF 2.70 Mb)
Part C (PDF 2.64 Mb)
Part D (PDF 2.43 Mb)
Part E (PDF 2.60 Mb)

• Dolan and Woeste developed some information on controlling vibration published in Structural Engineer magazine.
• APA Technical Note called Minimizing Floor Vibration by Design and Retrofit
  http://www.apawood.org/SearchResults.aspx?q=E710&tid=1
• Wood Design Focus paper by Dolan and Kalkert called “Overview of Proposed Wood Floor Vibration Design Criteria” (Vol. 5, #3).

Floor joist span tables are tabulated based on allowable deflection limits of L/360. Floor live loads range from 30 psf for sleeping areas to 40 psf for other occupancies. Ceiling joist span tables are tabulated based on allowable deflection limits of L/240.

Typically a user will know the span and desired spacing for a given application. The user can select a species, size, and grade for trial use. Using the Design Values for Joists and Rafters, the user determines the modulus of elasticity and bending design value of the species, grade and size of lumber. Bending design values are already adjusted for load duration and repetitive member factors in the Design Values Supplement. With this information the user enters the span table with the given modulus of elasticity and determines the allowable span for an estimated size and spacing. If the allowable span is greater than that required for the application, the species, grade and size selected should then be verified for bending strength. At the bottom of each table, required bending design strengths for specific joist spacing are tabulated. If the bending design value selected from the Design Values Supplement is greater than the tabulated required bending design value, then the species and grade chosen is adequate. If the bending design value is less than the tabulated value then the user can either select a deeper member, decrease the joist spacing or select a higher lumber grade, thus a higher bending design value. For either option, modulus of elasticity has to be re-evaluated to ensure the deflection limits are maintained. Linear interpolation for intermediate design values is permitted.

More details available in the tutorial.

No. An engineer or architect should design cantilever members. Design of cantilever beams involves many variables including load, cantilever span and interior or back span. Often the load is not a single uniform distribution over the length of the member, and other additional loads are present, such as point loads at the end of the member. Because the system is composed of two pieces: the cantilever span, and the back span, the placement and magnitude of load on these sections singly or combined will cause different stresses to develop in the member. The designer seeks to find the worst combination of loading that will impose maximum shear, bending, or deflection in the member.

American Wood Council’s 2001 Wood Frame Construction Manual has engineered and prescriptive provisions that may give guidance for typical cantilever cases. For example, the Engineered Design provisions for sawn lumber floor joists in 2.3.1.6 state the maximum overhang length is limited to the depth of the joist if the end of the cantilever supports a load bearing wall or shear wall (Figure 1, below).

When designed for additional loads, cantilevers are limited to 4 times the depth of the joist (Figure 2, below).

The cantilevered joist must be located directly over studs unless the top plates are designed to carry the loads. If the end of the cantilever supports a non-loadbearing non-shear wall, then the maximum overhang length is limited to one-fourth of the joist span (Figure 3, below).

Consult manufacturer’s recommendations if using I-joists. Prescriptive Design provisions found in 3.3.1.6.1 for sawn lumber floor joists are the same except that for roof live loads and ground snow loads less than or equal to 20 psf and 30 psf, respectively, cantilevers shall not exceed one-eighth of the joist span for lumber joists supporting only a roof with a clear span of 28 feet or less.

A variety of Span Table Documents and Span Calculator products are available for use in wood building design, complete with a tutorial for their use.

The online AWC Span Calculator performs calculations for ALL species and grades of commercially available softwood and hardwood lumber as found in the NDS Supplement. There are also several other online span tables available for various regional species and grades of lumber and loading conditions:

Canadian Span Tables and Calculator 
Southern Pine Span Tables 
Western Span Tables and Calculator

Rafter span tables are tabulated based on allowable deflection limits of either L/240 or L/180.

The L/240 limitation allows for attachment of a ceiling to the underside of the rafter by limiting possible cracking. Cathedral ceilings are an example of this type of application. The L/180 deflection limitation would apply to a rafter with no ceiling directly attached, so deflection is not a concern.

Roof live and snow loads range from 30 psf to 60 psf. Roof dead loads range from 10 to 20 psf.

Typically a user will know the span and desired spacing for a given application. The user can select a species, size, and grade for trial use. Using the Design Values for Joists and Rafters, the user determines the modulus of elasticity and bending design value of the species, grade and size of lumber. Bending design values are already adjusted for load duration and repetitive member factors in the Design Values Supplement. With this information, the user enters the span table with the given bending design value and determines the allowable span for an estimated size and spacing. If the allowable span is greater than that required for the application, the species, grade and size selected should then be verified for stiffness or deflection. At the bottom of each table required modulus of elasticity for specific joist spacing are tabulated. If the modulus of elasticity is less than the tabulated value then the user can either select a deeper member, decrease the joist spacing or select a high lumber grade, thus a higher modulus of elasticity. For either option, bending design strength has to be re-evaluated to ensure that strength limits are maintained.

Decking Span Tables

Redwood – Click “Deck Construction” to see their updated version
http://www.calredwood.org/literaturelibrary/

Southern Pine
http://www.southernpine.com/span-tables/

Western Red Cedar
http://www.realcedar.com/decking/products/

National Lumber Grades Authority’s rule #126 under all species that have been graded according to NLGA (which includes Ponderosa Pine) for Exterior Patio Decking provides grade rules as follows:

“Exterior patio decking rough or unsurfaced – kiln dried, air dried, or unseasoned 5/4″ to 2″ thicknesses, 4″ and wider for flatwise load applications where spans are not to exceed 16″ on centre.”

The American Wood Preservers Association (AWPA) establishes standards for preservative retention levels for wood used in construction

• McGraw-Hill publishes a Wood Engineering and Construction Handbook, which includes a chapter on Adhesives (Chapter 12). It is authored by Richard Avent, Ph.D., P.E. Contact information:Department of Civil and Environmental Engineering
  Louisiana State University
  3505B CEBA
  Baton Rouge, LA 70803
  USA

  Phone: (225) 578-8735
  Fax: (225) 578-8652
  Email: [email protected]
  Website: Department of Civil and Environmental Engineering (CEE)

   

• ASCE publishes a document called Evaluation, Maintenance and Upgrading of Wood Structures, 1982, which includes a chapter (Chapter 5) on methods of repair and case studies where epoxies were used to repair wood structural members.American Society of Civil Engineers
  1801 Alexander Bell Drive
  Reston, VA 20191

  Phone: (800) 548-2723
  Website: http://www.asce.org

   

• The American Institute of Timber Construction (AITC) publishes a document entitled Use of Epoxies in Repair of Structural Glued Laminated Timber (1990). It is available to download free from their website at https://www.aitc-glulam.org.

The Treated Wood Council has developed a fact sheet on CCA-preserved wood.

The requirement for panels or let-in bracing in the corners of conventionally-constructed walls is, in general a non-engineered detail that provides lateral resistance of the wall assembly and structure when subjected to lateral loads such as occur during wind or seismic events. Overturning restraint, in this case is provided by the dead load acting on the wall and/or anchorage provided by perpendicular walls. However, when openings occur near the corners, the aspect ratio (height/length) of the wall located at the corner will vary with the type of construction (braced wall panel vs. shear wall) used as well as the size of the opening.

Basic Requirements
Section R602.10.4 of the International Residential Code (IRC) provides basic wall bracing requirements and specifies the minimum length of braced wall panels for different types of exterior sheathing – in general this is 4 feet. Therefore, where an opening exists near a corner, the minimum length of braced wall panel required (at the corner and elsewhere) is 4 feet for an 8 foot high wall.

Using Continuous Structural Panel Sheathing
Using wood structural panel sheathing (OSB or Plywood) on all sheathable areas of all exterior walls and interior braced wall lines as well as having corners constructed in accordance with IRC Figure R602.10.5, can reduce the minimum length of braced panel required as per Table R602.10.5 (e.g. can reduce the min. 4 foot length to a 2 foot length of braced wall panel for an 8 foot high wall, or to a 2-1/2 foot length for a 10 foot high wall – provided the maximum opening height next to this braced wall panel is 65% of the wall height.

R602.10.6 provides further options where one can essentially use 2 foot 8 inch panels (min.) for walls up to 10 feet in height with no restriction on max. opening height – but this requires the use of tie-down devices, and other additional fastening and sheathing requirements.

Note that recent code change proposals for the upcoming 2006 IRC are looking to permit walls with 6:1 aspect ratios used with continuous structural panel sheathing.

AWC’s WCD #3. Design of Wood Formwork for Concrete Structures (T13). 1987 NO LONGER IN PRINT. For archival information, contact​ AWC.

APA-The Engineered Wood Association publishes Concrete Forming available for free on their website.

The American Concrete Institute (ACI) published the Guide to Formwork for Concrete available on their website.

Concrete Form Plywood
Concrete form plywood panels are manufactured in conformance with the requirements of the U.S. Department of Commerce Voluntary Product Standard PS 1, Structural Plywood. PS 1 establishes minimum requirements for the principle types and grades of construction and industrial plywood including wood species, veneer grading, glue bond, panel construction and workmanship, dimensions and tolerances, marking, moisture content, quality control and certification.

Concrete form meets the requirements for an “Exterior” bond classification and is manufactured with “B” face and back veneers and “C” or better inner plies. Bond classification is related to the moisture resistance of the glue bond under intended end-use conditions and does not relate to the physical (erosion, ultraviolet, etc.) or biological (mold, fungal decay, insect, etc.) resistance of the panel.

Class 1 concrete form plywood is designed to provide superior performance in the most demanding applications. A Class 1 panel, as defined in PS 1, is a panel with a Group 1 species in the face veneers, Group 1 or Group 2 species in the crossbands and Group 1, 2, 3, or 4 species in the center plies. A Group number is used to classify species covered by PS 1. Numbers range from 1 to 5. Strength and stiffness properties of species in Group 1 are typically highest, while the strength and stiffness properties of species in Group 5 are the lowest.

Structural I plywood used for formwork is manufactured with Group 1 species in all plies. It is specifically designed for applications where higher strength properties are required.

PS 1 is written in such a way that Class I or Class II concrete form plywood can only be so-designated if produced by manufacturers located in North America. Since many non-North American manufacturers produce concrete form panels, another grade marking approach is used in these situations. Such products cannot be identified as either Class I or Class II, but – under PS 1 – these products can be tested (by an accredited laboratory in accordance with approved acceptance criteria) to determine a Group Classification, which is then shown on the grade stamp. As a result, there is a designation: BB O & ES [BB grade, (release) oiled, and edge-sealed] for concrete form plywood manufactured outside of North America.

It is generally true that test reports must come from laboratories accredited (for the specific test method under consideration) by organizations such as the International Accreditation Service, Inc. (IAS), or by another accreditation body that is a signatory to the Mutual Recognition Arrangement (MRA) of the International Laboratory Accreditation Cooperation (ILAC). As regards evaluation reports requiring periodic inspections of the manufacturing facility by a third-party agency, the inspection agency must be accredited by IAS or by an accreditation body that is a partner of IAS in an MRA.

Yes. From section 9.1.3 of the NDS: The term “wood structural panel” refers to a wood-based panel product bonded with a waterproof adhesive. Included under this designation are plywood, OSB, and composite panels. The term “composite panel” refers to a wood structural panel comprised of wood veneer and reconstituted wood-based material and bonded with waterproof adhesive. The term OSB refers to a mat-formed wood structural panel comprised of thin rectangular wood stands arranged in cross-aligned layers with surface layers normally arranged in the long panel direction and bonded with waterproof adhesive. The term “plywood’ refers to a wood structural panel comprised of plies of wood veneer arranged in cross-aligned layers. The plies are bonded with an adhesive that cures on application of heat and pressure.

For additional information, contact the following organizations:

APA – THE ENGINEERED WOOD ASSOCIATION
7011 S. 19th Street
Tacoma, Washington 98466
253-565-6600
Fax: 253-565-7265
Website: http://www.apawood.org/

PFS-TECO
1507 Matt Pass
Cottage Grove, WI 53527
Phone: 608-839-1013
Website: https://www.pfsteco.com/

APA publishes information on how to deal with overdriven fasteners. www.apawood.org

The Midwest Plan Service publishes a Structures and Environment Handbook which address gussets in section 406.5 under Wood Truss Design. The most recent edition is a 1987 Revised 11th Edition.

Midwest Plan Service
122 Davidson Hall
Iowa State University
Ames, IA 50011-3080

Toll Free: (800) 562-3618
Customer Service: (515) 294-4337
Fax: (515) 294-9589
E-mail: [email protected]

Other info available at https://www-mwps.sws.iastate.edu/

The USDA Forest Products Lab has a publication called the Wood Handbook that contains information regarding finishes for wood products. View this information online at:
http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm

Chapters 14 and 15 may provide information specific to your needs. The TOC for both chapters is as follows:

Chapter 14 Wood Preservation (PDF 1.2 MB)

Wood Preservatives
Preservative Effectiveness
Effect of Species on Penetration
Preparation of Timber for Treatment
Application of Preservatives
Handling and Seasoning of Timber After Treatment
Quality Assurance for Treated Wood

Chapter 15 Finishing of Wood (PDF 2.2 MB)

Factors Affecting Finish Performance
Control of Water or Moisture in Wood
Types of Exterior Wood Finishes
Application of Wood Finishes
Finish Failure or Discoloration
Finishing of Interior Wood
Finishes for Items Used for Food
Wood Cleaners and Brighteners
Paint Strippers
Lead-Based Paint

The Forest Products Society also publishes a document called:
Building An Industrial Wood Finish

The information contained in this manual has been gleaned from the experiences of the author collected during more than 30 years as a supplier of wood finishes to manufacturers of finished wood products and as a consultant to the industry. The purpose of the manual is to help manufacturers gain a full understanding of all of the factors that impact the quality, durability, cost, and environmental impact of finished wood products. Four chapters cover: Finishing Products – multiple-step wood furniture finishes, kitchen cabinet and office furniture finishes, specialty wood finishes, and waterborne/water-based finishes; Executing the Wood Finish – wood finish application hardware options, examples of wood finishing manufacturing lines, and transfer efficiency and calculation of wood finish costs; Wood Finishes and the Environment – legal and regulatory issues and pollution prevention opportunities through hardware and finish product improvements; and Quality Control – white room wood preparation, wood finish variables and recommendations, finish inconsistencies/troubleshooting, the importance of lighting, and analyzing rejected pieces.

Publication #7247 (1 lb)
Available through their website:
http://www.forestprod.org/

Composite Panel Association

The USDA Forest Service Wood Handbook pages 17-2 through 17-5 contain material on wood mold and mildew.
Publication link: Forest Service Wood Handbook.

The Build Green: Wood Can Last for Centuries report explains why wood decays, alerts the homeowner to conditions that can result in decay in buildings, and describes measures to prevent moisture-related damage to wood.
Publication link: Build Green: Wood Can Last for Centuries.

Mold and Moisture in Homes

Mold. It’s all around us.  We use mold to make cheese, process wine, and produce helpful drugs such as penicillin.  We also see unwanted mold in places such as damp basements.  Mold even exists on human bodies.  So, one might ask, what’s causing the current questioning about mold?  There’s no easy answer to that question.  However, there are some reasonably straightforward facts about how and when mold might start to grow in or around your home.

Facts

FACT: Spores, the dormant form of mold, are in the air we breathe, the soil in our gardens, and in and around virtually every part of our homes.

FACT: Mold spores will not actively colonize, or grow, without adequate supplies of food, air, and moisture.  In typical homes, the normal control of moisture levels prevents colonization of mold spores.

FACT: A properly constructed building envelope is designed to keep the inside of your home dry (including the interior and concealed building spaces) to stop mold spores from becoming active.    This building envelope also insures that wood products quickly achieve and remain at a moisture level that will not support mold growth.

FACT: Except for cases in which moisture is artificially introduced into the structure (for example, by interior water leakage, unusually high interior humidity levels, or penetration of the building envelope), mold will generally not become active in your home.

FACT: All mold spores can not be permanently eradicated by cleaning or disinfecting.  While cleaning can remove spores present at the time, it will generally not protect surfaces against mold spores that arrive after cleaning.

FACT: Conditions that are sufficiently moist to support active mold colonization are also sufficiently moist to degrade the materials in your home.  For example, wood products may start to decay, metal products may begin to rust, and other products may begin to deteriorate.

Techniques to minimize mold problems in your home

Control build-up of moisture within your home.  Install and use ventilating fans in kitchens and bathrooms.  Be sure that fan exhausts are ducted to the outside.  Use dehumidifiers where necessary, but don’t allow the dehumidifier to become a source of mold itself.  Insulate any ducts which pass through unheated attic or crawl spaces.

If mold or mildew begin to grow in or on any part of your home, find the source of moisture intrusion and stop it.  If moisture intrusion has been occurring over time, hire a professional to examine the structure to determine if any permanent damage has occurred.

Naturally durable species are those that are naturally resistant to insect damage and moisture or decay.

Some of those species include cedar, black locust, and redwood. Also consider using pressure treated wood for such applications where durability is an issue.

Check out the USDA Forest Product Lab’s Wood Handbook for more information.

For information concerning metal plate connected wood trusses:
Truss Plate Institute
Structural Building Components Association

For information on bracing of wood trusses: Structural Building Components Association.

Breakaway walls or flood vents are not a choice. Vents can be placed in breakaway walls, but solid walls with vents cannot be used in place of breakaway walls. FEMA Technical Bulletin #9 outlines guidelines for breakaway walls.

Sometimes code officials are asked by landowners to approve rough-sawn (unsurfaced) lumber. This is a challenge since the code requires all lumber used in structures to be graded and stamped, something typically done at the mill after the lumber is surfaced. Since the surfacing (planing) of lumber can reveal defects that may affect the grade and which may go undetected in rough-sawn lumber, grading should be done by a qualified grading or inspection agency. The IRC and IBC permit a certificate of inspection from a qualified grading or inspection agency in lieu of grade stamps, but the certificate should contain clear information about the agency and the lumber being graded. Unique identifying marks should be applied to the lumber by the grading or inspection agency representative at the time of grading, or another positive identification method used. The marks or identifying method should be described in the certificate of inspection. The code official should not hesitate to require details of whatever identification method is used, and should inspect accordingly.

AWC has links to historic documents on our website here: NDS Archives

Designers can view and download copies of the 1922 Design Values for Structural Timber and the 1944 NDS on this page. Archive versions of the NDS are also available for a small fee.

Ecourses are also available relating to evaluating in-service structures. Both DES140 – Structural Condition Assessment of In-Service Wood and DES160 – Evaluation of Recommended Allowable Design Properties for Wood in Existing Structures can provide helpful information to professionals working with existing structures.

See also General FAQ, “Where can I find information on evaluation, maintenance, and repair of existing structures?”

Beam load tables in WSDD are tabulated based on spans from 4 to 32 feet and for lumber sizes from 2×4 to 24×24 inches.

Typically a user will know the span and load for a given application. The user can select a species, size, and grade for trial use. Using the Design Values for Wood Construction Supplement, the user determines the modulus of elasticity, bending design value, and shear parallel to grain design value of the species, grade and size of lumber. These design values need to be modified for all applicable adjustment factors including load duration and repetitive member factors from the Design Values Supplement and NDS. With this information the user enters the load table with the given bending design value and determines the allowable load for an estimated size. If the allowable load is greater than that required for the application, the species, grade and size selected should then be verified for stiffness and shear. Below each tabulated load value are the required modulus of elasticity and shear design value for the specific application. If the modulus of elasticity and shear design value selected from the Design Values Supplement is greater than the tabulated required modulus of elasticity and shear value, then the species and grade chosen is adequate. If the modulus of elasticity or shear design value is less than the tabulated value then the user can either select a larger member, or select a higher lumber grade. For either option, bending design strength has to be re-evaluated to ensure that strength limits are maintained. For multiple members or built-up members, the allowable load would be determined by dividing the actual load by the number of plies selected for that particular member. Linear interpolation for intermediate design values is permitted.

Wood Structural Design Data (WSDD) tabulates two different types of column load tables: simple solid columns and spaced columns.

Typically, a user will enter the tables with a known length for the column and a given load. The user can select a species, size, and grade for trial use. Using the Design Values for Wood Construction Supplement, the user determines the modulus of elasticity and compression parallel to grain design value of the species, grade and size of lumber. These design values need to be modified for all applicable adjustment factors including load duration from the Design Values Supplement and NDS. The user should determine the length to depth ratio based on the size of member selected. With this information the user enters the load table with the given modulus of elasticity and compression design value and determines the allowable load for the calculated length to depth ratio. If the allowable load is greater than that required for the application, the species, grade and size selected are adequate. If the allowable load is less than required then the user can either select a larger member, or select a higher lumber grade.

There are no specific provisions for connections for built-up beams. WCD#1, Details for Conventional Wood Frame Construction outlines the following general criteria:

Beams and girders are of solid timber or built-up construction in which multiple pieces of nominal 2-inch thick lumber are nailed together with the wide faces vertical. Such pieces are nailed with two rows of 20d nails-one row near the top edge and the other near the bottom edge. Nails in each row are spaced 32 inches apart. End joints of the nailed lumber should occur over the supporting column or pier. End joints in adjacent pieces should be at least 16 inches apart, Figure 15.

There is a General FAQ dealing with increased buckling capacity for built-up beams:
​“Is there a design method for increased buckling capacity of built-up wood beams?”

AWC’s Special Design Provisions for Wind and Seismic, Table 4.2D contains shear capacities for lumber sheathing attached straight and diagonally. Table 4.3D contains shear wall capacities for straight and diagonal lumber sheathing as well.

AWC also publishes Plank and Beam Framing for Residential Buildings (WCD-4) (T14). It shows how this floor and roof framing system, traditionally used in heavy timber structures, can be adapted to home building.

The International Building Code contains design capacities for diagonally sheathed lumber diaphragms in section 2306.3 Wood Diaphragms. Visit http://www.iccsafe.org for ordering information.

Analysis Methods for Horizontal Wood Diaphragms by Jephcott and Dewdney from proceedings of a Workshop on Design of Horizontal Wood Diaphragms (ATC-7-1) conducted by Applied Technology Council on November 19-20, 1980 (25 pages). Visit their website at http://www.atcouncil.org/ to order.

The “vented airspace” refers to spaces which have the ability to move air from the space that will be vented to the outside. This is a common practice in attics where the building codes require that the space be “vented” and they specify the amount of air movement by a percentage of the ceiling area (1/150 or 1/300 depending on the vapor barrier).

For more information, see WCD #6 – Design of Wood Frame Structures for Permanence. Download free here.

WCD #2 Tongue and Groove Roof Decking

Timber tongue and groove decking is a specialty lumber product, constituting an important part of modern timber construction, that can be used for many applications to provide an all-wood appearance. Nominal three and four inch decking is especially well adapted for use with glued laminated arches and girders and is easily and quickly erected. This document contains all that’s needed to design and construct tongue and groove wood roof decking.

AWC’s Wood Construction Data #4, Plank and Beam Framing for Residential Buildings (WCD-4). Shows how this floor and roof framing system, traditionally used in heavy timber structures, can be adapted to home building. 28 pages. (T14)

TR4 contains information on designing a Low-Profile Wood Floor System, test results, discussion and conclusions, and construction recommendations. * NO LONGER IN PRINT. (TR4) Published 1964. For archival information, contact AWC.

AWC’s The Wood-Frame House as a Structural Unit (TR-5) – Evaluates structural performance of a full-scale house subjected to simulated wind and gravity load combinations. (TR5) Download free.

Chapter 16 of the National Design Specification (NDS) for Wood Construction provides a code-recognized approach for determining the fire resistance of solid sawn, glulam, and select structural composite lumber (SCL) materials, including laminated veneer lumber (LVL), parallel strand lumber (PSL), laminated strand lumber (LSL), and cross-laminated timber (CLT). Design for Code Acceptance Document 2, titled “Design of Fire-Resistive Exposed Wood Members” (DCA 2) provides resources for users to calculate fire resistance for exposed wood members, in compliance with Chapter 16 of the NDS including flexural members (beams), compression members (columns), and solid lumber including decking and other structural members. Additional information including background, examples, and tables providing allowable load ratios for different member types and sizes can be found in Technical Report 10 (TR10).

See also:

• Other Fire Publications (DCA 1 -4)
• Design of Fire-Resistive Exposed Wood Members

In a double-shear connection, the main member is the member in the middle. The side members would be the outermost members.

Yes, the equations are structured that they will allow capacities to be calculated for any material being connected to wood, so long as the bearing design properties for the material are known. See 2015 NDS Chapter 11.2.3 and 11.2.4 and Technical Report 12.

Beam load tables in WSDD are tabulated based on spans from 4 to 32 feet and for lumber sizes from 2×4 to 24×24 inches.

Typically a user will know the span and load for a given application. The user can select a species, size, and grade for trial use. Using the Design Values for Wood Construction Supplement, the user determines the modulus of elasticity, bending design value, and shear parallel to grain design value of the species, grade and size of lumber. These design values need to be modified for all applicable adjustment factors including load duration and repetitive member factors from the Design Values Supplement and NDS. With this information the user enters the load table with the given bending design value and determines the allowable load for an estimated size. If the allowable load is greater than that required for the application, the species, grade and size selected should then be verified for stiffness and shear. Below each tabulated load value are the required modulus of elasticity and shear design value for the specific application. If the modulus of elasticity and shear design value selected from the Design Values Supplement is greater than the tabulated required modulus of elasticity and shear value, then the species and grade chosen is adequate. If the modulus of elasticity or shear design value is less than the tabulated value then the user can either select a larger member, or select a higher lumber grade. For either option, bending design strength has to be re-evaluated to ensure that strength limits are maintained. For multiple members or built-up members, the allowable load would be determined by dividing the actual load by the number of plies selected for that particular member. Linear interpolation for intermediate design values is permitted.

Wood Structural Design Data (WSDD) tabulates two different types of column load tables: simple solid columns and spaced columns.

Typically, a user will enter the tables with a known length for the column and a given load. The user can select a species, size, and grade for trial use. Using the Design Values for Wood Construction Supplement, the user determines the modulus of elasticity and compression parallel to grain design value of the species, grade and size of lumber. These design values need to be modified for all applicable adjustment factors including load duration from the Design Values Supplement and NDS. The user should determine the length to depth ratio based on the size of member selected. With this information the user enters the load table with the given modulus of elasticity and compression design value and determines the allowable load for the calculated length to depth ratio. If the allowable load is greater than that required for the application, the species, grade and size selected are adequate. If the allowable load is less than required then the user can either select a larger member, or select a higher lumber grade.

There are no specific provisions for connections for built-up beams. WCD#1, Details for Conventional Wood Frame Construction outlines the following general criteria:

Beams and girders are of solid timber or built-up construction in which multiple pieces of nominal 2-inch thick lumber are nailed together with the wide faces vertical. Such pieces are nailed with two rows of 20d nails-one row near the top edge and the other near the bottom edge. Nails in each row are spaced 32 inches apart. End joints of the nailed lumber should occur over the supporting column or pier. End joints in adjacent pieces should be at least 16 inches apart, Figure 15.

There is a General FAQ dealing with increased buckling capacity for built-up beams:
​“Is there a design method for increased buckling capacity of built-up wood beams?”

AWC’s Special Design Provisions for Wind and Seismic, Table 4.2D contains shear capacities for lumber sheathing attached straight and diagonally. Table 4.3D contains shear wall capacities for straight and diagonal lumber sheathing as well.

AWC also publishes Plank and Beam Framing for Residential Buildings (WCD-4) (T14). It shows how this floor and roof framing system, traditionally used in heavy timber structures, can be adapted to home building.

The International Building Code contains design capacities for diagonally sheathed lumber diaphragms in section 2306.3 Wood Diaphragms. Visit http://www.iccsafe.org for ordering information.

Analysis Methods for Horizontal Wood Diaphragms by Jephcott and Dewdney from proceedings of a Workshop on Design of Horizontal Wood Diaphragms (ATC-7-1) conducted by Applied Technology Council on November 19-20, 1980 (25 pages). Visit their website at http://www.atcouncil.org/ to order.

WCD #6 – Design of Wood Frame Structures for Permanence

The Southern Pine Council has information on termites and preservation against them at their website: http://www.southernpine.com/.

Termite Control: Results of Testing at the U.S. Forest Service is available from the USDA FS at http://www.srs.fs.usda.gov/pubs/viewpub.php?index=1482.

The “vented airspace” refers to spaces which have the ability to move air from the space that will be vented to the outside. This is a common practice in attics where the building codes require that the space be “vented” and they specify the amount of air movement by a percentage of the ceiling area (1/150 or 1/300 depending on the vapor barrier).

For more information, see WCD #6 – Design of Wood Frame Structures for Permanence. Download free here.

AWC’s Wood Construction Data #1 Details for Conventional Wood Frame Construction, which provides proper methods of construction in wood frame buildings, with information on features which contribute to the satisfactory performance of wood structures.

AWC publishes the Wood Frame Construction Manual for One- and Two-Family Dwellings to provide solutions based on engineering analysis, in accordance with recognized national codes and standards. Like conventional construction, the engineered solutions are provided in a prescriptive format.

WCD #2 Tongue and Groove Roof Decking

Timber tongue and groove decking is a specialty lumber product, constituting an important part of modern timber construction, that can be used for many applications to provide an all-wood appearance. Nominal three and four inch decking is especially well adapted for use with glued laminated arches and girders and is easily and quickly erected. This document contains all that’s needed to design and construct tongue and groove wood roof decking.

AWC’s Wood Construction Data #4, Plank and Beam Framing for Residential Buildings (WCD-4). Shows how this floor and roof framing system, traditionally used in heavy timber structures, can be adapted to home building. 28 pages. (T14)

AWC’s WCD #6, Design of Wood Frame Structures for Permanence. Text and detail drawings provide latest information on protection against moisture, termites, and decay. Emphasizes importance of proper design and construction to achieve permanent wood structures. 16 pages. (T16) Free download here.

AWC’s TR3. Details of test of unprotected laminated wood and rolled steel beams when simultaneously exposed to identical fire conditions. 8 pages. NO LONGER IN PRINT. (T23) Published 1979. For archival information, contact AWC.

AWC’s The Wood-Frame House as a Structural Unit (TR-5) – Evaluates structural performance of a full-scale house subjected to simulated wind and gravity load combinations. (TR5) Download free.

AWC’s a Performance Comparison of a Wood-Frame and a Masonry Structure (TR-8) – A study of the comparative costs and comfort in heating and cooling a wood-frame and a masonry test structure in the Phoenix, Arizona area. (T26) Download free here.

AWC’s Heat Release Rates of Construction Assemblies by the Substitution Method (TR-9) – Study describing efforts to develop measurement methods for determining the rate of heat release of full-scale assemblies. (T27) Download free here.

Chapter 16 of the National Design Specification (NDS) for Wood Construction provides a code-recognized approach for determining the fire resistance of solid sawn, glulam, and select structural composite lumber (SCL) materials, including laminated veneer lumber (LVL), parallel strand lumber (PSL), laminated strand lumber (LSL), and cross-laminated timber (CLT). Design for Code Acceptance Document 2, titled “Design of Fire-Resistive Exposed Wood Members” (DCA 2) provides resources for users to calculate fire resistance for exposed wood members, in compliance with Chapter 16 of the NDS including flexural members (beams), compression members (columns), and solid lumber including decking and other structural members. Additional information including background, examples, and tables providing allowable load ratios for different member types and sizes can be found in Technical Report 10 (TR10).

See also:

• Other Fire Publications (DCA 1 -4)
• Design of Fire-Resistive Exposed Wood Members

Yes, the assumption is that the connector will develop a hinge in the body of either the main member or side member(s), not in the gap.

For tapered tip fasteners, the main member is the one that contains the point of the fastener. For bolted connections, the distinction is less clear. In general, it is assumed the member which applies the load is the side member, but it actually doesn’t matter as long as the correct properties are used for the main and side members respectively.

In a double-shear connection, the main member is the member in the middle. The side members would be the outermost members.

Yes, the equations are structured that they will allow capacities to be calculated for any material being connected to wood, so long as the bearing design properties for the material are known. See 2015 NDS Chapter 11.2.3 and 11.2.4 and Technical Report 12.

The 2015 National Design Specification for Wood Construction (NDS) Chapter 16 and Technical Report 10 allows for the design of wood members exposed to fire.

Thermal expansion/contraction for wood is minimal. The USDA Forest Products Lab Wood Handbook, Chapter 3. Page 3-21 outlines thermal expansion coefficients for wood, which are almost microscopic. Any expansion joint would be based on roofing material requirements.