Electrical & Electric

Roof Structures | Roof Trusses

Factory Made Roof Trusses

Overview:

Roof construction is a construction specialty in itself. Not all carpenters are roofing specialists because roof structures involve skills that all carpenters may not have. Roofs are constructed in two ways, either by stick construction or with roof trusses. Stick construction is a term used to define the two different methods of how a roof is built.

A stick built room consists of individual pieces of lumber that are installed one at a time to make up the roof structure. The roof structure pieces consist of roof rafters, a ridge pole (the center point of the roof), collar ties, and overlays. The language can be confusing so let me explain some of the terms. 

Roof rafters:

The roof rafters are the basic structure that the roof sheathing is attached to. They’re made either from 2x6s, 2x8s, 2x10s, and sometimes 2x12s, depending on the building span and load requirements in the region where the building is built. In northern areas where snow is a factor the roof is designed to support heavy snow loads however, in regions where there is little or no snow the roof load is of less concern. The roof rafters are attacked to both sides of the ridge pole.  The ridge runs the full length of the roof. The roof rafters are usually placed 16 inches on center but then again that depends on the desired roof load and the size of the roof rafters.

Ridge Pole:

The ridge (ridge pole) is located at the top of the roof. The ridge runs the full length of the roof. The roof rafters are attached to both sides of the ridge, usually at 16 inches on center but then again that depends on the desired roof load and the size of the roof rafters.

Collar Ties:

Collar ties are usually made from 2x6s and attached to the roof rafters approximately two feet below the ridge. There purpose in to distribute the load of the roof evenly between the roof rafters on both sides of the roof. Collar ties are usually installed on every other set of roof rafters.

Overlays:

The overlays are usually 2x6s that run the width of the building and attach to the roof rafter where they sit on the walls. The overlays also serve as the ceiling joist for the room below. 

Roof Trusses:  

A roof truss is a one piece pre-fabricated frame. The pieces are assembled in jig and nailed together using steel plates. Roof trusses made the roof construction much easier. A builder simply provides the dimensions of the house to his supplier and the supplier orders roof trusses from a truss builder. The trust builder builds the trusses to the truss design requirements for the roof loads in the area of where the building is constructed.

Roof trusses can be made in any size to fit any building design. They make a stronger roof than stick built roofs and usually are a lot cheaper to use than the material required for a stick built roof by more than 20%. Although they are cumbersome to install they do make the overall construction of the roof much faster.

The trusses are usually placed 16 inches apart although they are often spaced 24 inches apart depending on their design and the load requirements of the roof. If the building has a complex roof design a combination of truss and stick construction is used to build the roof.

This is a basic explanation of roof structure and design. On small construction projects such as sheds and other out buildings, the roof is usually stick built but roof trusses can be manufactured to fit any roof design. I recommend using trusses because they are cheaper than stick roof construction, make a stronger roof, and enables you to complete the project much faster.

See related articles:

Floor Construction | Floor Joists

Roof Pitch

Roof Repair

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