Wood Needed to Build a Roof

Rafters and Trusses

• Rafters, the sloped framing members that form the basic structure of a roof, provide the support for the finished roofing material, such as asphalt shingles. Rafters come in various thicknesses and widths, such as 2-by-6s, 2-by-8s, and 2-by-12s. The thicker the wood, the further you can space rafters apart on the roof. A collar tie, a board nailed to the upper section of two opposing rafters, helps steady the roof framing. Trusses, triangular framing members held together at the joints with wood or metal fasteners, also see frequent use in home construction. The wood for both rafters and trusses can come from a variety of species, such as pine or spruce.

Plywood

• Plywood is one of the primary materials used for roof sheathing. Plywood consists of thin wood veneers glued together to a form a single panel. At first plywood was not suitable for exterior use, due to the lack of a waterproof bonding glue. In the 1930s, however, a waterproof adhesive was developed, and gradually the use of plywood for roofing started to expand. Plywood generally comes from hardwood species such as Douglas fir or softwoods such as southern pine.

OSB

• Another type of wood product used as a roof decking, "oriented strand board" or OSB, consists of panels or boards created from strands of wood mixed with a binding agent. Manufacturers subject the wood and binder to intense heat and pressure to form a single unified master material, which is cut to size to create the finished decking material. Some boards may have tongue-and-groove edges to facilitate connecting the panels.

Ridge Pole

• A wooden ridge pole spans the width of a roof and provides a backing to attach the upper ends of the rafters. A ridge pole might provide significant structural support to a rafter, in which case it's called a ridge beam. Ridge beams usually require wood at least 2 inches thick and 6 inches wide. When a ridge pole provides little or no structural support, it's called a ridge board and might consist of wood only 1 inch thick.

Roof Covering

• Although asphalt or composition shingles remain the most common type of roof covering for American homes, wood shake and shingles find frequent use as well. Wood shakes, which are split from blocks, have a more rustic and uneven appearance than wood shingles. Shingles typically taper toward the bottom and possess much smoother, uniform surfaces from one to another. Since wood decays from prolonged exposure to wet conditions, the U.S. Forest Service advises using wood shake and shingles treated with a chemical preservative.