What Choices of Materials are There for Roof Decking?

Roof decking is the solid surface to which the shingles or other roofing material is attached. Typically, the decking comes as sheets of plywood, wood boards, or planks. More recently, laminated roof decking has appeared on the market for situations in which the ceiling is exposed.

Lumber

Lumber used for roof decking, or sheathing, has to be graded at least No. 3 common. These typically softwood boards should be seasoned so that they will not shrink as they dry after shingles have been attached. For either pitched or flat roofs, 1-inch board will suffice unless the flat roof will double as a balcony. In that case, thicker boards are needed for the extra strength. The boards can run either horizontally or vertically. If horizontal positioning is chosen, the boards can be laid with no space (called closed) or with some space between each board. However, if the house is in a region that suffers from a great deal of wind-driven snow, it is recommended to leave no spaces. In addition, certain roofing materials will need a solid nail base, such as asphalt shingles, composition roofing, and sheet metal shingles. Spaces can be left if using wood shingles, but only if it is in an area that has no blizzards.

Plywood

Plywood is a more economical choice than boards for roof decking. Since plywood comes in 4 X 8' sheets, a large area can be covered quickly. Plywood decking gives a solid nail base with fewer joints to cause potential problems. Plywood is used most commonly for roof decking because of its affordability and easy installation. The thickness of the plywood will be decided by rafter spacing (longer spans need thicker plywood), the weight of the roofing material (heavier shingles need thicker plywood0, and typical ice and snow accumulation (heavy accumulation will need thicker decking).

Planks

Planks used for decking are at least 2 inches thick and have a tongue and groove to make joints stronger. These are typically used on a roof with a low or almost flat slope. The planks can be from 4 to 12 inches wide and 2 to 4 inches thick with lengths spanning from 6 feet to over 20 feet.

Some planks are laminated. If laminated, the core could be of one type of wood while the outside or inside face would be a different type of laminated wood. However, all of one type of wood could be used. These laminated planks are excellent for uses where the ceiling will be exposed all the way to the decking. The laminated side offers a pretty surface for inside.

Some planks are made of all-wood fiber. These planks have the best strength and insulating values. Not only is it resistant to weather and termites, it also has the convenience of four different thicknesses. Each panel has the tongue and groove joints and is coated with color on both sides at the factory.

Your choice of decking material will depend on many factors. First, your budget will determine which material is most affordable. You will also need to consider the size of the span between rafters, as well as the amount of weight that the roof may have to bear. Once you know how strong the decking will have to be, you can make an informed choice on your roof decking material.

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