I Beam Roof Rafters

Continuing on from part 3.

I beam roof rafters.

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. 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. Conventional framing the first thing to understand is how a roof framed with wood i joists differs structurally from a traditional stick framed roof.

Trusses use webs of 2x4s within the truss structure to support the roof. It is always better to have a large rafter rather than be concerned with a sagging roof. In addition wood i joists are typically stocked and readily available. Floor beam span tables of residential structural design we will now look at roof rafter and beam design.

Roof dead load of 12 psf asphalt shingles. Straight gable roof framing is assumed for selection table. A truss on the other hand is only made up of 2x4s and is often pre fabricated in a factory. Floor live load of 40 psf between the kneewalls.

Before you cut your boards you ll need to measure the width of your building and calculate the exact length of each rafter. Rise and run means that a 6 12 pitch roof has 6 of rise vertical for each foot of run horizontal. Let s consider a basic gable wood roof framing design. They are ideal for long spans including continuous spans over intermediate supports.

The image below shows a cross section of our simple 12 x 13 house from the joist span tables section of this tutorial. Here we have a wood framed gable roof. Because i joists are straight and true it s easier for builders to avoid crowning and maintain a level framing surface. The roof rafters provide integral structural support to the roof.

I joists are used extensively in residential floor and roof framing. Rafter spans can be extended slightly beyond what the rafter tables suggest when there is a cantelever extending beyond the supporting wall. Structures such as sheds or barns can be frames with rafters every 24 again make sure to consult local codes. Attic storage load of 20 psf live load outside the kneewalls.

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. Roof rafter slope between 8 12 and 12 12.