plywood sheathing
Using ½ inch plywood, or OSB, blackboard or gypsum board in exterior walls without a suitable layer of rigid foam insulation is a common cause of thermal problems.
If your home is energy-inefficient and uncomfortable, traditional sheathing options may be contributing to it.
Plywood sheathing uses and pros
Plywood and other traditional sheathing materials are good to give strength to the walls and to help them to resist to wind, rain and other type of loads.
They are, in many cases, an integral part of the building - tying together the studs and giving strength and a solid nailing base for siding.
Types of plywood panels
When choosing, do not forget to buy plywood, OSB or wafer-board panels rated as wall sheathing. Take also into account the thickness issue: 5/16 inch and other thin panels are usually bad options for walls; 1/2-inch panels are a much better choice.
Sizes vary, but 4 by 8 feet sheets are the most common sizes. When installing plywood sheets allow an expansion gap of 1/16 inch between the panel ends and also an 1/8 inch between the edges.
Wood and Steel studs are thermal bridges
As alluded before, the problem with plywood sheathing (and other traditional sheathing materials) is that it doesn't provide much insulation value to the walls and the home.
By themselves, they do not prevent heat and cold to pass through the wood and steel structures of the walls, or through ductwork, wiring, plumbing and other construction elements in the walls (thermal bridging). And since siding do not prevent it either, discomfort and energy-inefficiency becomes big problems in many plywood sheathed homes.
Wood panel sheathing and moisture problems
Plywood and OBS and other wood boards sheathing may also pose moisture problems.
Wood-based sheathing products, by themselves, do not prevent moisture to move into the wall cavities, unless the walls have a house-wrap building membrane behind the siding, properly installed.
Image, from Dow: plywood sheathing doesn’t prevent heated and cold air to pass through the walls, and it’s prone to moisture problems.
Alternatives to plywood sheathing
Fortunately, there are now new and well tested alternatives to plywood sheathing, namely foam insulated sheathing.
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