Roof Rafter Length Tables

Steep roof rafter length calculation example 1.

Roof rafter length tables.

The length of the rafter. Roof rafter span use this table to determine the maximum lengths of roof rafters based on species and grade of lumber spacing dimensions load and slope. Use this table to determine the maximum lengths of floor joists based on species of lumber joist spacing and joist size. Rafter span tables use these tables to determine lengths sizes and spacing of rafters based on a variety of factors such as species load grade spacing and pitch.

On the framing square blade face using the common rafter length per foot run line in the table look along the blade under the inch number 18 we see 21 63. The respective lengths for those two rafters and add them together. 18 12 roof slope rafter lengths. Let s figure the rafter length for an 18 in 12 roof.

The spans in this table are based on a maximum supported rafter span of 16 feet where the supported span is the total horizontal distance spanned by the roof rafters divided in half not the diagonal distance or the length of the rafter. The run of the rafter. So this table could accommodate a house with a total rafter span or house width of 32 feet. Span tables for purlin supporting rafters to bs 5268 7 6 imposed loads of 0 75 kn m snow load are applicable to most areas where the altitude does not exceed 100 metres refer to bs 6399 3 imposed loads of 1 kn m snow load are applicable to most areas where the altitude exceeds 100 metres but does not exceed 200 metres but excluding parts of scotland pennines north east england.

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. Includes result for hip valley factor slope factor and the roof slope in degrees. Tail or eave length.

Calculate the length of a rafter from the roof slope ratio of inches per foot and a building width measurement. The tail or eave overhang must be added to the rafter length. 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. Using the 7 inch rise table and our 15 run the common rafter length is 17 43 8.

This is the rafter length from the top cut to the seat plumb mark. The rise of the rafter. 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. 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.

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