Posts that were made alluding to different prescriptive methods are outside of the provisions of the code (2006 IRC, Section 802.2). There are beam span tables in the WFCM.hip and valley beams in Table 3.28 and ridge beams in Table 3.29B.Ĭlick to expand.The rafter span tables in the IRC do not cover your situation. Where the roof pitch is less than three units vertical in 12 units horizontal (25-percent slope), structural members that support rafters and ceiling joists, such as ridge beams, hips and valleys, shall be designed as beams.
Hip and valley rafters shall be supported at the ridge by a brace to a bearing partition or be designed to carry and distribute the specific load at that point. At all valleys and hips there shall be a valley or hip rafter not less than 2-inch (51 mm) nominal thickness and not less in depth than the cut end of the rafter. Ridge board shall be at least 1-inch (25 mm) nominal thickness and not less in depth than the cut end of the rafter. Rafters shall be framed to ridge board or to each other with a gusset plate as a tie. Components of roof-ceilings shall be fastened in accordance with Table R602.3(1). Roof-ceilings shall be designed and constructed in accordance with the provisions of this chapter and Figures R606.11(1), R606.11(2) and R606.11(3) or in accordance with AFPA/NDS.
The framing details required in Section R802 apply to roofs having a minimum slope of three units vertical in 12 units horizontal (25-percent slope) or greater. At slopes less than 3:12 you essentially have a floor, so it is the supporting construction that has to be beefed up.
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