How To Figure Out Roof Trusses

The truss calculator will determine your roof trusses based on key inputs related to the pitch span and overhang of your roof.

How to figure out roof trusses.

Equation a2 b2 c2. C rafter length. The formula for truss loads states that the number of truss members plus three must equal the twice the number of nodes. If the number of members is labeled m and the number of nodes is labeled n this can be written as m 3 2 n.

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. If this distance measures 4 inches you have a 4 in 12 pitch. If you add an eaves overhang dimension then the amount the rafter sticks passed the wall will be added to the rafter length. 8 inches and you have an 8 in 12 pitch.

Given pitch and a horizontal area measurement multiply the horizontal area by a correction factor corresponding to pitch provided in the table below to determine the actual area of the roof to be used in the roofing material calculator. Already having the rise will make it easy to determine the rafter length by loading the numbers into the equation chart. Includes result for hip valley factor slope factor and the roof slope in degrees. Builders often prefer roof trusses to traditional stick framed roofs because they re quick to install.

If you can t get the heel height most residential trusses will have a 3 top cord. Both sides of the equation should be equal in order to end up with a stable and secure roof structure. A roof truss is a. Calculate the length of a rafter from the roof slope ratio of inches per foot and a building width measurement.

Calculate the height of a common truss using the building width and the slope of the roof. Use a tape measure to measure the entire width of your building. Depending whether the roof area is measured horizontally possibly from a drawing or photograph a correction factor is necessary to determine the actual area of the roof. Measure as precisely as possible down to the 1 4 inch 0 64 cm 1 8 inch 0 32 cm or 1 16 inch 0 16 cm.

Before you start cutting you first need to determine how long your roof rafters need to be and the angles at which you ll cut the top and bottom of the rafter. On a ladder beside the roof place the level a foot or so up the roof hold it level and measure from the 12 inch mark on the level s bottom straight down to the roof. They also eliminate the need to figure and cut complicated roof angles.