I Beam Roof Rafters

A truss on the other hand is only made up of 2x4s and is often pre fabricated in a factory.

I beam roof rafters.

Before you cut your boards you ll need to measure the width of your building and calculate the exact length of each rafter. Ceiling joist span use this table to determine the maximum lengths of ceiling joists based on species of lumber joist spacing and joist size. Attic and floor dead load of 10 psf. If you re framing a gable roof on a new house or building a shed or even a doghouse with a gable roof you ll need to cut a number of roof rafters.

Because i joists are straight and true it s easier for builders to avoid crowning and maintain a level framing surface. Straight gable roof framing is assumed for selection table. I joists are used extensively in residential floor and roof framing. Attic storage load of 20 psf live load outside the kneewalls.

Continuing on from part 3. Here we have a wood framed gable roof. If your project had a rafter length of 8 or less a safe and strong method is to use 2x8 framed 16 on center. Floor beam span tables of residential structural design we will now look at roof rafter and beam design.

The roof rafters provide integral structural support to the roof. Roof dead load of 12 psf asphalt shingles. The image below shows a cross section of our simple 12 x 13 house from the joist span tables section of this tutorial. Rise and run means that a 6 12 pitch roof has 6 of rise vertical for each foot of run horizontal.

Rafter spans can be extended slightly beyond what the rafter tables suggest when there is a cantelever extending beyond the supporting wall. It is always better to have a large rafter rather than be concerned with a sagging roof. Let s consider a basic gable wood roof framing design. Conventional framing the first thing to understand is how a roof framed with wood i joists differs structurally from a traditional stick framed roof.

They are ideal for long spans including continuous spans over intermediate supports. Roof rafter slope between 8 12 and 12 12. 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. Floor live load of 40 psf between the kneewalls.

In addition wood i joists are typically stocked and readily available. A rafter beam is usually larger than a 2 4 large homes may have rafters that are 2 12 or more. Kneewall weight of 40 plf.