Roof Decking and Sheathing

Decking (or Sheathing) makes up the surface that the roofing materials such as asphalt shingles or wood shakes are attached to. This surface is usually made up of plywood, wood boards, planks, or OSB and is exterior or exposure grade. This ensures they have been treated with waterproofing coats and can better handle rain fall during your roofs construction.


Oriented Strand Board (OSB) is made from compressed wood strands mixed with wax and adhesive. A typical OSB board consists of about 50 layers of these wood strands. OSB is often looked at as a cheaper alternative with less quality than plywood. However OSB actually has several advantages over plywood. Its more square and sheets differ from each other much less than with plywood, and are capable of being made into larger sheets. OSB is stronger than plywood, with screw hold being about the same. With all these benefits at a cheaper price, the only problem occurs when moisture is brought into the picture. If OSB is exposed too much water, the ends will expand up to 15% of its natural size. However, as long as OSB is installed properly with good ventilation this shouldn't be a problem.

Plywood is made from thin sheets of veneer, which are peeled away from a log. These sheets are then laminated together to form plywood. Unlike OSB, when plywood expands from water exposure it doesn't just expand on the edges, but evenly throughout the panel.

While OSB and plywood are the most popular in decking and sheathing, there are other options to look at. There is straw board, recycled paperboard, gypsum, cementations board, and foam sheathing.