![]() 3 and 3-1/2 Comes with instruction manual including rafter tables. 21.63 inches of rafter length per unit (one foot) of run Rafter Run Distance 10 ft or 10 units Rafter Length 10 units x 21.63' per unit Rafter Length 216.3' or we can divide by 12 to get feet and fractions Rafter Line Length ridge to top plate outer face 216.3 / 12 18.025 ft. Or 22 in the in field, and the fraction ½, the 1 in the n field and 2 in the d fieldĮnter the ridge board the same way as the overhang using the appropriate fields.Īnd the 8 for the roof pitch has only one field. As a saw guide, stair layout tool or rafter tool, Johnsons 12 rafter square will. ¾ inch: the 3 here is the n value, the numerator, and the 4 is the d value, the denominatorįor the overhang 22 ½" can be added to the in field as 22.5 Otherwise, enter the 44 feet in the ft field If you know what 44' 6 ¾" is in decimal, you can add this in the building width ft field ![]() The roof pitch is 8:12 (it rises 8 inches in a one-foot run). ![]() In making your choice, consider how you will insulate your insulate your roof. Another option are 2 X 8 rafters spaced 24 inches o.c. The overhang for the rafter is 22 and ½ inches, and you are using a 1 ½ inch ridge board. The table states that 2 X 6 rafters spaced 16 inches on center (o.c) can span a maximum distance of 13 feet 5 inches. The building width is 44 feet 6 and ¾ inches If you enter a value for the ridge board, then the calculator will subtract half of this amount from the rafter length. If you add an eaves overhang dimension, then the calculator will add the amount the rafter sticks passed the wall to the rafter length. The calculation includes results for hip/valley factor, slope factor and the roof slope in degrees. Calculate the length of a rafter from the roof slope ratio of inches per foot and a building width measurement.
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