Rafter Lengths And Roof Construction

Rafter is a sloping beam usually wood that supports a pitched roof.

Rafter lengths and roof construction.

Pitch is the incline of the roof represented as the ratio of rise to the span twice the run. Determine the camber along the timbers length. Calculate the length of a rafter from the roof slope ratio of inches per foot and a building width measurement. Height of the scaffold.

The number of rafters needed will be determined by the length of your roof. There could be many rafters supporting a roof. Before you can mark the rafter lengths and layout check the camber of the timber. Roof rise this should be calculated from the base of the roof to the highest point of the roof gable the peak.

If you plan to have overhang etc. Half building width minus 1 2 ridge thickness. All roof rafters should be identical so follow the same steps to measure the plumb cut tail cut and birdsmouth cut. The run of the rafter.

This calculator helps you make the rafters of the suitable sizes required for your roofing. Allow for ridge thickness when determining rafter run to outer wall. See rafter run to outer wall calculator below. Note that this is not the actual length of the rafter.

The results are automatically fired. If you add an eaves overhang dimension then the amount the rafter sticks passed the wall will be added to the rafter length. Calculate the length of common rafters with this free and easy online tool by entering a dimension for the roof width selecting a pitch for the roof and the thickness of the ridge. Includes result for hip valley factor slope factor and the roof slope in degrees.

Here the number is 941 86 inches. The rafter member will be longer. Rise and run means that a 6 12 pitch roof has 6 of rise vertical for each foot of run horizontal. Here the number is 1166 66 inches.

The rise of the rafter. It is the length of this portion of the rafter. Rafters are commonly spaced about 24 inches 61 cm apart. 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.

For example if the roof rises 4 feet and the span is 16 feet twice the run then the pitch is 4 16 or 1 4. Rafter run outer wall this should be measured starting from the center of the roof span and then extending to the very edge of the exterior wall. Lengths of roofing timber almost always bow slightly. Print full scale rafter cut templates and birdsmouth templates fold template over rafter to mark or cut through.

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.