What Underlayment to Use for Wall Sheathing

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Wall sheathing is the covering on the exterior of the house, over the frame. This underlayment is the base on which siding and wall insulation veneer is nailed onto the wall. The weather conditions of your area will determine the kind of underlayment material you need for sheathing.

Importance of Wall Sheathing

The basic importance of wall sheathing is to strengthen the walls and protect them from the effects of different weather conditions. Siding and veneer insulation attached to the sheathing prevents the penetration of water droplets into the house. However, water vapor can still infiltrate through this insulation. Wall sheathing underlayment prevents the vapor from penetrating into the building.

Best Underlayment Material

Plywood is the best underlayment material for wall sheathing. Oak, walnut, birch, and maple are some of the prime sources of hardwood plywood. Hardwood plywood is the best material for wall sheathing. Besides being strong to provide the protection needed for your building, it is very easy to work with. Plywood comes in varying degrees of thickness ranging from 3/4, 1/2, and 1/4 inches. The latter is the minimum thickness applicable for wall sheathing underlayment.

Besides thickness, plywood also varies in grading and the grading system uses letters A to D. Grade A represents the best quality of plywood, free of blemishes and sanded smooth. Grade B has small blemishes while C has obvious patches. Grade D is rough with knots and holes. There are, however, basic types of plywood designed to meet different wall sheathing needs as outlined below.

Types of Plywood

    Interior plywood - This is well finished on both sides. You may use it as an interior wall sheathing underlayment.

    Exterior plywood - It is suitable for use on either the interior or the exterior wall of the building and has a higher resistance to moisture and water vapor than the interior plywood.

    Marine plywood - It serves as an exterior wall sheathing underlayment in areas with high humidity. It has high-quality waterproof adhesives to provide protection against moisture infiltrating into the building.

    Structural plywood - It is the strongest and most stable type of plywood. It is suitable for areas that are prone to hurricanes and strong winds. This type of plywood provides extra support to the building by holding the frame of the house together to prevent destruction by strong winds.

      Purchasing Plywood for Wall Sheathing Underlayment

      Guided by the above properties for the different types of plywood, purchase the type that suits the weather conditions of your area. Note the number of plywood sheets required to fit the walls of your entire building. Add an extra piece in case you need it. The plywood comes in sheets measuring 2x4 feet. Nail the plywood sheets onto the 2x4-foot frame panels. By doing this, you can be sure that very little if any moisture, will seep into the building.