Section 704.2 of the 2009 and 2012 International Building Code (IBC) has its source in the legacy building codes and was primarily intended to address steel construction. The current text first appeared in the 2009 IBC, but was actually part of the 1999 BOCA National Building Code and 1994 editions of the SBCCI Standard Building Code and the ICBO Uniform Building Code. 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.
This section is NOT typically applied to wood construction. New language in both the 2009 and 2012 IBC has been added to clarify this point. There are two specific provisions of the code that support this position.
When a building is Type IV construction (Heavy Timber), Table 601 does not require a fire-resistance rating for any building element except the exterior walls, which by definition must be noncombustible or use fire retardant treated wood. The fire-resistance in Type IV buildings is established by meeting the minimum dimensions for each building element specified in the subsections of 602.4, based on the principle that wood retains its strength as it burns and larger dimension elements have more inherent fire-resistance. To avoid confusion about the possible application of Section 704.2 (Column protection) in Type IV construction, a sentence was added to the end of Section 602.4.1 in the 2012 IBC, which states “Protection in accordance with Section 704.2 is not required.” (Note: the first printings of the 2012 IBC did not show this sentence, but ICC has issued an erratum.)
For wood columns in buildings of Type IIIA, IIIB, or VA construction (there are no pertinent fire-resistance rating requirements for Type VB construction) fire-resistance could be accomplished by testing or any of the other five alternatives permitted by IBC Section 703.3. Calculation methods for determining the fire-resistance rating of exposed wood members, which are found in AWC’s National Design Specification® (NDS®) for Wood Construction and referenced in Section 721.1 of the code, could be used, by evaluating the size of the wood member in relation to the imposed loads. In this case, Section 704.2 would have no application, since protection of the column is not required for it to be fire-resistance rated, and to require additional individual protection of the column when concealed in a rated assembly is certainly not the intent of the code. This was clarified in the 2012 IBC, which adds these words at the beginning of Section 704.2 (Column protection): “Where columns are required to have protection to be fire resistance rated . . .” (no change to the rest of the section).
Additionally, some columns within fire-resistance rated walls of light-frame construction are addressed directly in Section 704.4.1 (Light-frame construction) and can be a part of a fire-resistance rated wall assembly without additional protection. That section states:“King studs and boundary elements that are integral elements in load-bearing walls of light-frame construction shall be permitted to have required fire-resistance ratings provided by the membrane protection provided for the load-bearing wall.”
If the designer chooses to achieve a required fire-resistance rating (for instance, in a Type IIIA or VA building) by wrapping the column with gypsum or other materials, then this protection would need to be continued through all concealed spaces.
What is the correct application of 2009/2012 IBC Section 704.3 (Protection of the primary structural frame other than columns) to wood construction?
Section 704.3 also is NOT typically applied to wood construction.
Definitions for “primary structural frame” and “light-frame construction” were included in Chapter 2 of the 2009 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, not a primary structural frame. 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.
See PDF Version