Rafter/ceiling joist connections and rafter/tie connections shall be of sufficient size and number to prevent splitting from nailing. Where rafter ties are spaced at 48 inches (1219 mm) o.c., the number of 16d common nails shall be two times the number specified for rafters spaced 24 inches (610 mm) o.c., with a minimum of six 16d common nails where no snow loads are indicated. Where rafter ties are spaced at 32 inches (813 mm) o.c., the number of 16d common nails shall be two times the number specified for rafters spaced 16 inches (406 mm) o.c., with a minimum of four 1 6d common nails where no snow loads are indicated. Rafter tie connections shall be based on the equivalent rafter spacing in Table 2308.10.4.1. Rafter ties shall be spaced not more than 4 feet (1219 mm) o.c.
Where ceiling joists or rafter ties are not provided at the top of the rafter support walls, the ridge formed by these rafters shall also be supported by a girder conforming to Section 2308.4. The connections shall be in accordance with Tables 2308.10.4.9.1, or connections of equivalent capacities shall be provided. Where ceiling joists are not parallel to rafters, an equivalent rafter tie shall be installed in a manner to provide a continuous tie across the building, at a spacing of not more than 4 feet (1219 mm) o.c. Ceiling joists shall have a bearing surface of not less than 1 1/2 inches (38 mm) on the top plate at each end. Ceiling joists shall be continuous or securely joined where they meet over interior partitions and fastened to adjacent rafters in accordance with Tables 2308.10.4.9.1 to provide a continuous rafter tie across the building where such joists are parallel to the rafters. To calculate maximum spans of species not shown above, use the Span Calculator or the Span Tables for Joists and Rafters on the American Wood Council website.Ceiling joists and rafters shall be nailed to each other and the assembly shall be nailed to the top wall plate in accordance with Tables 2304.9.10.1.
Attach the ties to the sides of the rafters. Purlins should be mitred at hips and lip cut to accept the bottom of the hip rafter. Align the lower edge at each end with the marks on the rafters.
ROOF RAFTER TIES CODE
To calculate maximum rafter spans using different design criteria (load, snow load, spacing, grade, etc.), for these common lumber species, see the International Residential Code (IRC). Position a collar tie flat against the corresponding sides of a pair of opposing rafters. The above spans are based on American Softwood Lumber standard sizes. Rafters with ceiling not attached to rafters, ground snow load = 50 psf, dead load = 20 psf, deflection limit L/180 The following span table uses a moderate snow load of 50 psf, but yours could be more or less. Consult your local building code authority to determine the snow load in your area. Note: Snow load can be very specific to the actual location of a structure.
Rafter Span Tables Rafters with ceiling not attached to rafters, live load = 20 psf, dead load = 20 psf, deflection limit L/180 The braces need to be supported by a bearing wall, as shown in the diagram above.Įxample: In the rafter span table below, the highlighted cell (13-0), indicates that 2" x 8" Douglas Fir rafter, with a grade of #2, spaced 24" apart, can have a maximum span of 13 feet - 0 inches (13-0) if designing for a live load of 20 psf, and dead load of 20 psf. Note also that you can break up the span of a rafter by adding a purlin and bracing to the underside. When calculating the maximum span of a rafter, use the horizontal distance between two vertical supports.
0 kommentar(er)
