Roof Rafter Length Formula

Includes result for hip valley factor slope factor and the roof slope in degrees.

Roof rafter length formula.

The run of the rafter. Calculate the length of a rafter from the roof slope ratio of inches per foot and a building width measurement. If you are calculating rafter length from the center of the ridge beam as shown below you will need to subtract half of the thickness of the ridge beam from the top end of the rafter. Step 4 add the measurement for the overhang the eaves on the outside wall to the result obtained in the rafter guide to determine the overall rafter length.

Here are the equations you may use to solve for the length of the slope and the rafter. Rafter rise run this formula is from the pythagorean theorem rise run pitch use this when you express the pitch in percent pitch tan angle use this when you express the angle of the roof pitch in degrees. Using the appropriate roof pitch table in a rafter cutting guide such as 4 12 determine the length of each rafter based on the correlating measurement shown for 7 feet. 1 1543 x 1 610 1 858m.

Rise and run means that a 6 12 pitch roof has 6 of rise vertical for each foot of run horizontal. Height of the scaffold. All we do now is use a calculator to multiply 1 610 by the measurement in the book. For example if the ridge beam is 1 5 inches thick subtract 3 4 of an inch from the overall rafter length.

The length of rafter per meter of run is 1 1543. This means that for every 1m the rafter travels horizontally the angled length of the roof will be 1 1543m. If you add an eaves overhang dimension then the amount the rafter sticks passed the wall will be added to the rafter length. The rise of the rafter.

Input the rafter span on the flat eave overhang and pitch of the roof. When building a roof how do you calculate the length of the rafters. Use our online rafter length calculator to quickly compute the length of the shed roof rafter by entering the measurements of overhead length of roof span pitch or angle. Rafter length using angle v r 2cos a rafter length using pitch v r 2 sqrt 1 p 2 where v overhang r roof span p pitch.

This calculator is to be used as an estimating tool only. 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. Click the button to calculate the stock size needed for this job.