Truss Options

Gable-end Trusses

Strictly speaking, gable-end “trusses” are not trusses. They are frames built in the shape of the other trusses in a package. Instead of a series of interlocking triangles, they have vertical pieces set at intervals of 16 in. or 24 in. for attaching sheathing and siding. However, this configuration gives the gable frame little tensile strength and it must rest on the end wall of the house. Using gable-end trusses saves time by eliminating the need to frame a gable-end wall.

Drop-top Gable-end Truss

Where rake overhangs are planned, truss suppliers can fabricate drop-top gable-end trusses. These are dropped the width of the top chord (usually 31⁄2 in.) from the common trusses in the package. After you set all the trusses, you can install a rake that passes over the drop-top truss and ties into the first truss inside the wall.

Scissor Trusses

Scissor trusses are used to construct cathedral ceilings in rooms with wide spans between bearing walls. Because these trusses exert no thrusting force on the walls, horizontal restraints, such as exposed beams or cables, are not necessary.

Attic Trusses

Attic trusses are designed with open spaces above the bottom chord that can be used for storage or for living space.

Cantilever Trusses

To support the roof over a porch without using posts, designers sometimes specify cantilever trusses.

Valley Trusses

When a house has one section running perpendicular to another, the intersecting roofs form valleys. To build these valleys with trusses, you run the first roof frame straight through the main section of the house. After sheathing the main house, use step-down valley trusses to build the intersection are on top of the roof deck.

Girder Trusses

On some houses, valley trusses are used in conjunction with girder trusses to create a wide opening between the main house and the intersection wing.

Girder trusses are typically made from several trusses that are fastened together on site. Because these multi-ply trusses support a huge amount of weight, they should never be designed on site. The trusses and the mechanical fasteners used to tie them together must be specified by the truss fabricator.

On these houses, the girder trusses are set first, extending across the opening to the intersecting wing. Then, when the trusses from the main rectangle of the house are set, the ends adjacent to the wing are supported by metal hangers affixed to the girder truss.

After the common trusses are set, valley trusses are installed on top of them to form the valleys.

Hip Trusses

Girder trusses are also used for hip roof packages. After setting the girder truss a specified distance from the corner, hip jack trusses and end jack trusses are attached to the girder truss with metal hangers.

Master and Split Trusses

When the plan calls for a large framed opening in the roof, as would be required for many chimneys and skylights, truss designers use master and split trusses. The master trusses work like trimmer rafters, carrying the weight of the framing below and above the opening. Like girder trusses, master trusses are often made up of multiple plies of trusses fastened together on site.

The top and bottom of the opening are made from header trusses attached to the master trusses with metal hangers. Split trusses are then attached to the header trusses to fill above and below the opening.

Other Shapes

Trusses can be made for a variety of roof styles, including dual-pitched, gambrel, and mansard roofs.