I Beam Roof Rafters

I joists are used extensively in residential floor and roof framing.

I beam roof rafters. It is always better to have a large rafter rather than be concerned with a sagging roof. Because i joists are straight and true it s easier for builders to avoid crowning and maintain a level framing surface. Roof dead load of 12 psf asphalt shingles. Here we have a wood framed gable roof.

Floor beam span tables of residential structural design we will now look at roof rafter and beam design. Trusses use webs of 2x4s within the truss structure to support the roof. Rise and run means that a 6 12 pitch roof has 6 of rise vertical for each foot of run horizontal. Roof rafter slope between 8 12 and 12 12.

In addition wood i joists are typically stocked and readily available. A truss on the other hand is only made up of 2x4s and is often pre fabricated in a factory. Before you cut your boards you ll need to measure the width of your building and calculate the exact length of each rafter. Straight gable roof framing is assumed for selection table.

Our roof rafter calculator tools are handy for calculating the number of rafters needed rafter length calculator lineal feet of rafter board feed in ridge and sub facia and the total board feet in the roof. In a typical roof framed with dimension lumber the rafters rest on the exterior wall top plate at the lower end and bear against a ridge board at the top. A rafter beam is usually larger than a 2 4 large homes may have rafters that are 2 12 or more. If your project had a rafter length of 8 or less a safe and strong method is to use 2x8 framed 16 on center.

Let s consider a basic gable wood roof framing design. The image below shows a cross section of our simple 12 x 13 house from the joist span tables section of this tutorial. Kneewall weight of 40 plf. Floor live load of 40 psf between the kneewalls.

The roof rafters provide integral structural support to the roof. Structures such as sheds or barns can be frames with rafters every 24 again make sure to consult local codes. Attic and floor dead load of 10 psf. Attic storage load of 20 psf live load outside the kneewalls.

Rafter spans can be extended slightly beyond what the rafter tables suggest when there is a cantelever extending beyond the supporting wall. Ceiling joist span use this table to determine the maximum lengths of ceiling joists based on species of lumber joist spacing and joist size. Continuing on from part 3.