Roof Truss Guide

Basic Gable

• Basic gable roof trusses have a bottom chord which goes from wall to wall, two top chords or rafters which form the pitch or slope of the roof to a peak and some type of internal braces called webs between the chords to support the top. The most basic type is called Fink or W because the braces are in a W pattern. They will span up to 33 feet. There are least four variations, with different brace patterns, depending on the width or span required.

Inside Space

• At least two styles of truss are made with steeper pitches and higher peaks to accommodate more attic space or a room inside the truss. These trusses have a second horizontal chord between the bottom chord and the peak, to form a ceiling, with a vertical brace between the peak and this cross chord. The amount of space inside the truss varies with the height and pitch of the roof.

Scissors

• Another style with more internal space is a scissors. These are made with two bottom chords, which are angled to form a sloping ceiling inside the house. There are at least three styles of these, with bracing varied depending on the width. Another style with extra inside space is called studio. These also have two bottom chords but at different heights so one ceiling section will be higher.

Special Types

• Special truss types include gambrel and Polynesian. Gambrel is the traditional "barn" roof, with two or more slopes on each side from a center peak. Gambrel truss bracing depends on the amount of internal space needed and whether there are two or three slope angles. Polynesian roofs also have two slopes on each side, but one angle is very low and there is a steep peaked area in the center.

Hips

• Hip roofs, which slope to a common eave on four sides, require special trusses. The center portion of a hip roof is framed with common gable trusses, but special hip trusses are used on the ends to provide the different slope angles required.

Flat

• Some flat or low-slope roofs also are framed with trusses, typically with two flat chords at top and bottom and varying types of brace in between. Some have the two chords parallel, others use a horizontal bottom chord with a top that is slanted at a very low pitch or angle. Braces are either vertical or angled or a combination.