Do I need a vapor control layer?

Putting an insulating layer on the outside of the sheathing, especially in cold climates, reduces the vapor problem. When the exterior warms, water does not condense and enter the walls, removing the need for an interior vapor control layer.

Where is the vapor control layer used?

The vapor control layer is used on the internal side, or the warm side, of the insulation. Doing this would stop warm, moist air from entering the structural elements. In cold climates, this vapor control layer is installed behind the drywall and is required by building code in most North American jurisdictions.

Is a vapor control layer waterproof?

The main job of the vapor control barrier is to limit the amount of moisture aka stop water in all forms from getting through.

In-Depth Product Guide

Vapor Control Layer

FAQs

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The vapor control layer or VCL limits the amount of moisture entering the wall cavity and ceiling through diffusion. The vapor control layer is used interchangeably with the vapor barrier and vapor retarder. The vapor control layer is a clear polyethylene plastic sheeting and usually 6-millimeters thick. In cold climates, this vapor control layer is installed behind the drywall and is required by building code in most North American jurisdictions.

A vapor control layer or a vapor barrier is only as good as its installation. Seams must be sealed with tape and acoustical caulk so that air and water vapor don't simply pass through openings and into a wall cavity or attic.

As a home becomes more airtight, it is essential to ensure enough fresh air in the house. An air exchanger such as a heat recovery ventilator or an energy recovery ventilator may be required to maintain air quality.

Look for a thicker plastic (minimum 6 mil.) that is more resistant to rips and tears.

Since it prevents 'heated' or 'cooled' indoor air from exiting a house, polyethylene vapor barrier can save on energy required to re-heat or re-cool replacement outdoor air.

The first type of house wrap used for residential construction was in the form of asphalt-saturated felt, which dates back to the 1800s. At the time, felt was made by recycling old rags.