Do I Need a Vapour Barrier?

You’re building a wall. Maybe you’re putting on an addition or finishing off your basement, or maybe you are just about to undergo a major renovation that requires taking the existing wall down to the studs. Whatever your reason you are now looking at finishing a new wall. Whether you are doing it yourself or hiring a contractor, it is a helpful to know a little about proper construction. Your first job after the studs are in place is to fill those walls with insulation.

After the insulation is in place you will want to add a vapour retarder, sometimes called a vapour barrier, if you need one. Not every wall does. A vapour retarder is a material used to prevent water vapour from diffusing into the wall, ceiling or floor during the cold winter.

Whether or not you need a vapour retarder hinges on three main factors your climate, your home and the location of the wall you’re insulating.

To know if you need a vapour retarder, ask yourself a few basic questions:

Map: Insulation Institute

What is my climate? If you live in a mixed climate – hot and humid with several heating months in the winter, you probably need a vapour retarder. Specifically, if you live in climate zones 4C (marine), 5, 6, 7 and 8. Not sure of your climate zone? You can check here.

What is my cladding type? According to the U.S. Census Bureau 2009 statistics, more than half of all new homes are clad with absorptive materials such as brick, stucco, wood, fibre cement or stone. These moisture-retaining claddings can worsen moisture challenges in the wall cavity. They have the potential to release moisture into the structure, creating an inward vapour that doesn’t exist with vinyl siding.

Where is the wall located? If you are adding an exterior wall, anywhere in the house, and you answered yes to either of the above questions, you should consider using a vapour retarder.

Vapour Retarder Use and Placement

In certain climates, vapour retarders can be a vital part of the wall construction. However incorrect use can lead to additional moisture problems. Consult an insulation professional in your area if you are unsure where or how to install a vapour retarder or consider a vapour retarder that provides some degree of additional flexibility, like a smart vapour retarder. A smart vapour retarder is able to adapt its permeability to allow the wall to dry should moisture get trapped in the wall cavity.

A smart vapour retarder is a vapour retarder material with the unique ability to react to changes in relative humidity by altering its physical structure. This material adapts to let moisture out of the wall whether the humidity levels are higher on the outside of the wall (winter) or the inside (summer). A smart vapour retarder is a good solution for areas of mixed climate.

Wall construction is important to creating a healthy, comfortable home. Read more about vapour retarders and learn how they can affect the health of your home.

Learn more about Membrain, a smart vapour retarder.