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Does Vapour Barrier Lead to Mold and Rot in Basements?

Polyethylene vapour barrier has been an integral part of residential insulation in Canada for more than 40 years. It is used to slow the migration of water into the walls of your home. By contrast, an air barrier, such as the Tyvek wraps that you might sometimes see sheathing the outside of a new home build, is used to slow the migration of air.

Barrier Method Controversy

While a Canadian building standard, interior polyethylene vapour barrier is not without its share of controversy, especially in recent years. While most industry professionals opposing the usefulness of vapour barrier seem to hail from the more southern states in the US, there are some Canadian building science professionals who believe that this commonly used insulation material may be doing more harm than good.

The reasoning behind the opposition of vapour barrier is the belief that with today’s homes being insulated for maximum, air-tightness, it means that the polyethylene is trapping moisture in the wall assembly. If this is the case, it can lead to mold and rot. Those in favour of using vapour barrier believe that colder, dryer climates like those in the northern US and in Canada are not as susceptible to problems of moisture in the walls.

However, it is believed by some that the rise of air conditioning use in Northern households over the last 20 years is imparting more moisture into homes, and thereby creating problems with moisture retention. It has been said that the methodologies and practices once put in place to prevent homes from getting wet are now responsible to preventing them from properly drying. If this is the case, what alternative are available to Canadian homeowners?

Where Do Canadian Pros Stand on This Issue?

We would love to hear the opinions of Canadian building professionals on the issue of polyethylene vapour barrier and its alternatives. If you’re a building pro or someone with an interest in building science, please visit us on Facebook and let us know what you think about this issue.

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