Traditional Roof Trusses

Standard Gables

• There are at least a dozen standard gable roof truss types, to span roofs with widths from 16 to 80 feet. All have the same basic design, a horizontal bottom chord that spans from wall to wall, two angled top chords that meet at a center peak and some type of bracing between the chords to support the rafter chords. Both upright and angled braces are used, depending on the style and size of the truss.

Common Types

• The most common gable trusses are Fink and Howe, with Fink the more widely-used. Fink is also called a W style, because its four braces, two on each side of the peak, are angled so they form a W pattern. Howe is a K style because its combination of three upright and two angled braces make a sort of K. Either type can span more than 30 feet of roof width.

Gusset Strength

• All modern trusses have joints fastened with strong metal plates called gussets, which give the truss its great strength. Gussets go across the joint and have spikes, which are driven into the wood sections being joined, across the wide sides of the boards. Traditional rafters are fastened with nails driven through the narrow part of the board. The combination of more connectors across joints on the wide board provide greater strength.

Angles

• Basic gable-style trusses can be adapted to various roof pitches or slopes by changing the angles of the top chords and length of the internal braces. Fink and Howe trusses can handle angles up to 35 degrees, which accommodates the vast majority of houses. Most are built with 2-by-4-inch lumber, but some situations with heavier loads on the roof will use 2-by-6-inch boards.