When it comes to getting a roof put on your home, whether it's new construction or an older home, the sheathing is the very first consideration. The sheathing, sometimes called roof decking, is what goes over the roof trusses, providing a barrier from the weather and a "lid" over the house. When an old house is in need of a new roof, sometimes a contractor will just go over the previous layer if there is only one layer. This is standard operating procedure for a single previous roof. But if it has already been gone over once, then it is time for a total tear off.
This is the perfect opportunity to take a closer look at the existing sheathing and underlying rafters. Here is a look at the various roof decking options.
Plywood comes in assorted grades, ranging from A to D, with A being the best. CDX plywood is lower quality plywood that is suitable for exterior use. Plywood is relatively inexpensive, lightweight, and comes in the industry standard 4x8 sheets. Roofers usually use one half-inch thick or thicker sheets.
Oriented Strand Board
Also known as OSB, oriented strand board is similar to plywood in terms of the size of the sheets, but it is manufactured differently. Little slivers of wood are mixed with water-resistant adhesives and formed into a new sheet of a manufactured wood material. OSB sheets need to be at least one half-inch thick as well.
Both plywood and OSB are the most popular choices used by roofing professionals. Oriented strand board is slightly cheaper than plywood. It is also lighter in weight. But many contractors feel plywood is the better choice should the decking inadvertently become wet over the course of time, even though the OSB is manufactured with an adhesive that is supposed to prevent moisture issues.
Tongue & Groove
In more temperate climates, tongue and groove planks are sometimes used. This method is especially good if an attic space will be used as living space. The tongue and groove method is more attractive to look at, and the interior side can be stained or painted. This method would also apply to a room such as a great room with a cathedral ceiling, for example.
While the grooved planks form a tight interlocking bond, in colder climates, you would want your attic insulated, which would cover the tongue and groove. As this is more expensive, it's not a choice frequently used widescale.