![]() ![]() ![]() ![]() The braces shall be spaced not more than 4 feet (1219 mm) on center and the unbraced length of braces shall not exceed 8 feet (2438 mm). Purlins shall be continuous and shall be supported by 2-inch by 4-inch (51 mm by 102 mm) braces installed to bearing walls at a slope not less than 45 degrees (0.79 rad) from the horizontal. Purlins shall be sized not less than the required size of the rafters that they support. Installation of purlins to reduce the span of rafters is permitted as shown in Figure R802.5.1. TABLE R802.4(2) CEILING JOIST SPANS FOR COMMON LUMBER SPECIES (Uninhabitable attics with limited storage, live load = 20 psf, L/Δ = 240) CEILING JOIST SPACING (inches) For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot = 0.0479 kPa. TABLE R802.4(1) CEILING JOIST SPANS FOR COMMON LUMBER SPECIES (Uninhabitable attics without storage, live load = 10 psf, L/Δ = 240) CEILING JOIST SPACING (inches)Ĭheck sources for availability of lumber in lengths greater than 20 feet. For other grades and species and for other loading conditions, refer to the AWC STJR. ![]() Spans for ceiling joists shall be in accordance with Tables R802.4(1) and R802.4(2). Collar ties shall be not less than 1 inch by 4 inches (25 mm by 102 mm) (nominal), spaced not more than 4 feet (1219 mm) on center. Collar ties or ridge straps to resist wind uplift shall be connected in the upper third of the atticspace in accordance with Table R602.3(1). Where ceiling joists or rafter ties are not provided, the ridge formed by these rafters shall be supported by a wall or girder designed in accordance with accepted engineering practice. Span tables are based on the International Building Code and International Residential Code, and are available for download. Rafter ties shall be not less than 2 inches by 4 inches (51 mm by 102 mm) (nominal), installed in accordance with the connection requirements in Table R802.5.1(9), or connections of equivalent capacities shall be provided. Learn how to use span tables to calculate joist and rafter spans in one- and two-family dwellings, and the design values for dimension lumber. Where ceiling joists are not parallel to rafters, rafter ties shall be installed. Where ceiling joists are not connected to the rafters at the top wall plate, joists connected higher in the atticshall be installed as rafter ties, or rafter ties shall be installed to provide a continuous tie. Span tables Rafters Roof slope 22.5° or more but less than 30°, Imposed load 0.75 kN/m², C16 timber, no plasterboard Permissible Clear Spans for Rafters (to BS 5268-7. Ceiling joists shall be continuous or securely joined in accordance with Table R802.5.1(9) where they meet over interior partitions and are nailed to adjacent rafters to provide a continuous tie across the building where such joists are parallel to the rafters. I first saw this on the fine home building site.Ceiling joists and rafters shall be nailed to each other in accordance with Table R802.5.1(9), and the rafter shall be nailed to the top wall plate in accordance with Table R602.3(1). There are some green builders in VT who say you don't need a vapour barrier because the cellulose stops almost all infiltration and can absorb a lot of water and let it back out to the interior. If I wanted the beam and plank look and didn't have to worry about code I think I would explore site built Larson trusses and blown in cellulose. I always thought that the roof was one of the drawbacks with straw bale. I also built roofs on top with 2x12 rafters and fiberglass to do the same thing.īack when I was reading about super insulation there were folks using TGI's in Alaska with post and beam roofs and walls I think. The span of each rafter shall be measured along the horizontal projection of the rafter. That's why SIP's are such a good marriage with beams. Spans for rafters shall be in accordance with Tables R802.5.1(1) through R802.5.1(8). It wasn't that hard to do but I never felt that good about it. 4" foam 2x4 strapping with another layer of 1 1/2" foam cut to fit between the strapping. I have done the foam bit to winterize porches that were beam and 2圆 T&G. Is the black poly a vapor barrier? why Black? ![]()
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