rafters or for every third pair of 16-in. In most circumstances, workmanship does not warrant that assumption but with special inspection from the EOR, it may be okay. They are generally required every 4 ft., which means that you need a rafter tie only for every other pair of 24-in. Rafter ties are not necessary if the roof works as a folded plate, but that would require special attention to the nailing of the deck to the rafters, nailing to the top wall plate and nailing to the ridge board. Rafter ties amount to an additional framing member that runs above the ceiling joists and that connects opposing rafters. However, when ceiling joists run perpendicular to roof rafters, rafter ties should be installed to resist the thrust that the rafters exert on the exterior walls. Common ceiling joists function as rafter ties when they run parallel to the rafters. On the other hand, rafter ties are installed between opposing rafters as close to the top plate as possible. However, in those cases when they are specified, collar beams are usually installed in the upper third of the roof between opposing rafters.
#Roof rafter ties code
The correct phrase as used in textbooks and when specified is collar beam.Īs I stated in my earlier Q&A response, international residential code does not require collar beams. But isn’t rafter tie just another way to say “collar tie”?Ĭontributing editor Mike Guertin replies: Collar tie is a colloquial phrase that you usually won’t find in construction or engineering documentation even though the words are commonly used among builders, architects and homeowners. 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.With all of the discussion and controversy surrounding the question of removing collar ties, the 1998 international code does discuss “rafter ties” in section 802.3. 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). 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
#Roof rafter ties software
Design engineers use computer software to design simple to elaborate configurations of trusses, based on the architectural plan. Where rafters and joists are made on-site, trusses are built in a factory setting. 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. A roof truss can be described as a rafter, cripple, joist, and collar tie all in a single, preformed unit. Attach the ties to the sides of the rafters. Align the lower edge at each end with the marks on the rafters. Note also that you can break up the span of a rafter by adding a purlin and bracing to the underside. Position a collar tie flat against the corresponding sides of a pair of opposing rafters. When calculating the maximum span of a rafter, use the horizontal distance between two vertical supports.
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