Residential Roofing Rafter Size

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.

Residential roofing rafter size.

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. In making your choice consider how you will insulate your insulate your roof. Required size for a given span. Another option are 2 x 8 rafters spaced 24 inches o c.

Calculate the length of a rafter from the roof slope ratio of inches per foot and a building width measurement. Rise and run means that a 6 12 pitch roof has 6 of rise vertical for each foot of run horizontal. Input the rafter span on the flat eave overhang and pitch of the roof. If you add an eaves overhang dimension then the amount the rafter sticks passed the wall will be added to the rafter length.

Spacing should be interpreted as the centre to centre distance between adjacent parallel members. If your project had a rafter length of 8 or less a safe and strong method is to use 2x8 framed 16 on center. Roof load width rlw and floor load width flw can be determined from as1684 or from the images below. Includes result for hip valley factor slope factor and the roof slope in degrees.

The closer the rafters are to each other the stronger the roof will be. 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. Typical rafter spacing codes will specify a minimum spacing of 16 inches 19 2 inches or 24 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. 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. Click the button to calculate the stock size needed for this job. If your local building authority has a rafter spacing code you may not space rafters wider than required by code.