FAQ Category: Design for Code Acceptance (DCA) 1- 7

What are the requirements for locations of diagonal knee braces?

Knee braces should only be installed at corner posts. Interior posts should not have knee braces. Diagonal bracing can contribute to the stiffness of the deck and, therefore, cause additional lateral loads on the posts. Since center posts receive more vertical load than corner posts, additional lateral load can cause overstress. For this reason, DCA6…

Can I specify proprietary fasteners such as gun nails?

Proprietary products are permitted as approved by the local authority having jurisdiction.   This FAQ is based on the presentation of BCD303 – Design for Code Acceptance No. 6 – Prescriptive Residential Deck Construction Guide. Also, see Page 12 of Part II: Design Values for Structural Members for background on the Wet Service Factor.

In Prescriptive Residential Wood Deck Construction Guide (DCA 6) Table 2, why, for a given joist size, does the overhang span sometimes increase as joist spacing increases?

For this table, a uniform load on the joist never determines the allowable span of the overhang. Only deflection due to the point load or ¼ the length of the main span (whichever controls) limit the length of the overhang. Under a single point load, deflection at the overhang decreases as the main span decreases….

Figure 18 of DCA6 prohibits attachment of the ledger to an overhang or bay window. Does this include small cantilevers on the house such as brick ledge cantilevers or cantilevers to accommodate exterior insulation?

Yes. Any cantilever of the house floor structure over a bearing wall in which the house bandjoist or rimjoist does not have full bearing support would qualify as a cantilever per DCA6. In such cases, a non-ledger deck or engineering evaluation would be required. Where the house rimjoist has full bearing support of a wall…

How are deck beams or girders attached to posts?

Beginning with the 2015 International Residential Code, wood beams or girders supporting deck floor joists or gravity loads from other sources must have full bearing at supporting posts. At ends of wood beams or girders, a minimum of 1.5” of direct bearing on wood or 3.0” on concrete or masonry is required. Beams and girders are…

Does the wet service factor apply for residential wood decks?

Wood members that are protected from direct moisture in building construction reach an equilibrium moisture content below 19%, which is considered dry service conditions. Design values assigned to lumber and engineered wood products in the AWC National Design Specification® for Wood Construction (ANSI/AWC NDS®) and the NDS Supplement are based on the assumption of dry service conditions. When wood…