Roof Rafter Length Formula

Calculate the length of a rafter from the roof slope ratio of inches per foot and a building width measurement.

Roof rafter length formula.

Enter the value for the roof width outside to outside in feet inches and fraction inches and fraction or use the inches box to enter a value in decimals if that is your preference. Before you can mark the rafter lengths and layout check the camber of the timber. Calculate the rafter length substituting these values into the following formula. For example a roof with a span of 20 ft and a rise of 7 feet needs rafters that are the square root of 400 49 21 2 feet.

Slope the slope of a roof is represented as x 12 where x is the number of inches in rise for every 12 inches of run this is very useful information for many purposes especially for roof framing the slope sometimes called pitch is calibrated on speed squares. Rafter rise run 1 5 6 2 25 36 38 25 rafter 38 25 6 18 m calculate the roof pitch as the proportion of rise and run. Includes result for hip valley factor slope factor and the roof slope in degrees. C rafter length.

While making roofing for your house with the roof rafters it is important to know the rafter length to make the roof seat perfectly on the rafter. This does not include the extra length required for the overhangs. Determine the camber along the timbers length. 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.

The roof pitch calculator is a convenient online tool you can use to quickly assess the pitch of your roof to determine the length of rafters you need. After finding out your roof pitch angles you can use the calculator to perform the calculations for you instead of doing them manually. The length of the rafter. Rise and run means that a 6 12 pitch roof has 6 of rise vertical for each foot of run horizontal.

Roof pitch calculator results explained. The rise of the rafter. Height of the scaffold. The run of the rafter.

Already having the rise will make it easy to determine the rafter length by loading the numbers into the equation chart. Lengths of roofing timber almost always bow slightly. The dotted line is how the rafter length measurement is used measure from the point at the top down the length and plumb a line there. Angle the angle of a roof is the same as the roof s slope except instead of being.

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