The Importance of the Vapour Barrier for Building Envelopes

In Canadian homes, air tight construction can greatly improve the atmosphere within a house as well as the longevity and structural integrity of a house. Building envelopes have not always been air tight, to the detriment of many buildings. Frequent reconstruction or renovation are required when vapour and air of different temperatures are allowed to move freely through a building envelope and therefore the rest of the building. In order to best protect a Canadian home, air tight air and vapour barriers should be part of the building envelope.

Condensation Control

The role of a vapour barrier is to stop condensation from forming in the dark layers between areas in the home which are warm and the cooler air outside of it. Water vapour is found in warmer air, where there is more space between molecules to trap and hold the moisture. Think about how a warm room will cause standing water to disappear while in a cold room the water will simply stay on the ground. Water evaporates more quickly when the air is warm and warm homes are typically moist, especially with people living, cooking, and breathing indoors.

As the warm air passes through inner walls, it cools and leaves condensation within the walls. Windows that are poorly insulated are a perfect example, as the moisture condenses on the inside of windows where indoor air is warm and outdoor air is cold.

The Vapour Barrier in Canadian Homes

Cooler climates, like we have here in Canada, require that the vapour barrier must be inside the insulation. This keeps water vapour from condensing inside the wall, where it can cause water damage and mould to form. Air tight construction in Canadian homes is key to keeping water vapour from moving between temperature zones where condensation can occur.