Residential Roofing Rafter Size

This calculator is to be used as an estimating tool only.

Residential roofing rafter size.

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 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. Spacing should be interpreted as the centre to centre distance between adjacent parallel members. If you add an eaves overhang dimension then the amount the rafter sticks passed the wall will be added to the rafter length.

If your local building authority has a rafter spacing code you may not space rafters wider than required by code. In making your choice consider how you will insulate your insulate your roof. Calculate the length of a rafter from the roof slope ratio of inches per foot and a building width measurement. Required size for a given span.

Typical rafter spacing codes will specify a minimum spacing of 16 inches 19 2 inches or 24 inches. 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. Decreasing the distance between rafters to 12 inches however increases the maximum span to 14 feet 4 inches. The table states that 2 x 6 rafters spaced 16 inches on center o c can span a maximum distance of 13 feet 5 inches.

Includes result for hip valley factor slope factor and the roof slope in degrees. Click the button to calculate the stock size needed for this job. 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. Roof load width rlw and floor load width flw can be determined from as1684 or from the images below.

The closer the rafters are to each other the stronger the roof will be. 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. 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.