Residential Roofing Rafter Size

If you add an eaves overhang dimension then the amount the rafter sticks passed the wall will be added to the rafter length.

Residential roofing rafter size.

Required size for a given span. Rise and run means that a 6 12 pitch roof has 6 of rise vertical for each foot of run horizontal. Another option are 2 x 8 rafters spaced 24 inches o c. The closer the rafters are to each other the stronger the roof will be.

Spacing should be interpreted as the centre to centre distance between adjacent parallel members. This calculator is to be used as an estimating tool only. Typical rafter spacing codes will specify a minimum spacing of 16 inches 19 2 inches or 24 inches. Click the button to calculate the stock size needed for this job.

Input the rafter span on the flat eave overhang and pitch of the roof. Decreasing the distance between rafters to 12 inches however increases the maximum span to 14 feet 4 inches. For example 2 by 6 rafters made from select structural grade douglas fir that are required to support a live load of 20 pounds per square inch can have a maximum horizontal span of 11 feet 4 inches. In making your choice consider how you will insulate your insulate your roof.

Roof load width rlw and floor load width flw can be determined from as1684 or from the images below. As a general rule roofs that have a high human occupancy rate should be framed with rafters every 16 structures such as sheds or barns can be frames with rafters every 24 again make sure to consult local codes. For example in the rafter span table below the highlighted cell in the 40 live load table indicates that 2 x 8 southern yellow pine joists that have a grade of 2 that are spaced 24 apart can have a maximum span of 10 feet 3 inches 10 3 if designing for a live load of 40 lbs ft 2. Maximum clear span of rafters in metres for roof pitches of between 15 and 45 degrees roof pitch between 15 and 22 5 degrees with rafter spacing strength class c16 size of rafters in mm.

If your local building authority has a rafter spacing code you may not space rafters wider than required by code. Visit the roof framing page for more information on cutting roof rafters and visit the roof pitch calculator for determining rafter lengths based on rise and run. Our roof rafter calculator tools are handy for calculating the number of rafters needed rafter length calculator lineal feet of rafter board feed in ridge and sub facia and the total board feet in the roof. Includes result for hip valley factor slope factor and the roof slope in degrees.