Planning Ahead

Sheathing Membranes and Air Barriers

Sheathing membranes are required beneath siding, stucco or masonry veneer. Membranes which are permitted for this application are intended to be of the breather type, permitting any humidity built up in the walls to vent to the outside. At the same time, these membranes are designed to resist bulk water from penetrating the exterior walls, generally caused by wind-driven rain.

Air barriers are required in ail exterior components of the building envelope to prevent air leakage which can cause internal moisture damage and waste energy. In some cases, the requirements for the air barrier and the vapour barrier are met by using polyethylene loeated on the interior which is careful ly sealed at joints and penetrations. In other cases, the air barrier may be a separate membrane applied to the exterior face of walls.

When combining the requirements (or sheathing membranes and air barriers, the following points should be considered:

Ensure that the air barrier membrane conforms to the requirements for sheathing membrane materials. It must allow water vapour (humidity) to escape from inside to outside.

-t Install the air barrier membrane so that it is continuous and airtight. Typically, taping joints and sealing penetrations is required to provide an effective barrier to air leakage.

When exterior insulating sheathing is used, products which incorporate an air barrier membrane may also be considered.

In most cases, when a sheathing membrane is required, it makes sense to provide a material which also serves as an air barrier membrane.

When in doubt, consult your local building department prior to construction for acceptable materials and methods.

It is important to resolve the type of air barrier and how it will be installed prior to the installation of wall sheathings and exterior finishes. Plan ahead carefully by referring to the requirements for air barriers in the Vapour and Air Barriers chapter.

(200 mm) off the ground and 2 in. (50 Metal arid Vinyl Sidings mm) from an adjoining roof surface. Metal and vinyl sidings are used

Methods of flashing over window and extensively and are virtually mainte-

door openings and between different nance free since they come with types of wall covering are described in factory-finished surfaces. They are the chapter on Flashing. produced in different shapes and

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