What is Airtightness in a House?
Residential construction has come a long way in the last few decades, with a greater focus on energy efficiency and sustainability. One of the key components of a highly energy efficient building is airtightness. Simply put, airtightness refers to how well a building is sealed against air leaks, and it has a major impact on energy efficiency and comfort.
Why Does it Matter?
In a poorly sealed building, air can leak in and out through various gaps and cracks. This leads to energy losses, as warm air escapes in the winter and cool air escapes in the summer. Due to these losses, buildings require more energy to maintain a comfortable temperature, leading to higher energy bills and a larger carbon footprint. According to Natural Resources Canada, air leakage can account for up to 30% of a building's heat losses. In extreme cases, air leaks can also lead to mold growth and poor indoor air quality.
If you add up all the air leaks in the average home built before 1940, they would be equivalent to having a 50cm diameter hole in your wall.
Doesn't a House Need to "Breathe"?
You may have heard it said that a house needs to "breathe". What that means is that fresh air needs to be brought into the house to replace stale, contaminated, or moist air. While this is important for maintaining good indoor air quality, houses that leak air in an uncontrolled way waste a lot of energy.
Built Tight + Ventilate Right
The solution to achieving good indoor air quality is to build an airtight, energy efficient building, and then exchange air in a controlled way using mechanical ventilation. Modern homes have systems that bring in a specific amount of fresh air throughout the day based on the size of the house and the humidity inside. Simple systems may have an exhaust fan on a timer, or a fresh air intake that adds air to the heating system. Even more advanced systems such as Heat Recovery Ventilators (HRV) and Energy Recovery Ventilators (ERV) actually capture the heat from the outgoing stale air and use it to pre-heat the incoming fresh air with up to 90% efficiency.
What Can I Do?
There are many sources of potential air leakage in a home. The most common areas are chimneys, windows, doors, ventilation fans, and the intersection of the wood frame and the concrete foundation of the house. Essentially, any place where there is a hole in the building envelope, there is potential for air leakage. Simple solutions include adding weather stripping or replacing seals on doors, windows, and attic hatches. You can also spray foam and insulate the place where the floor joists rest on the foundation wall, and ensure that all chimneys, as well as bathroom and kitchen exhaust fans are equipped with a damper which blocks the flow of air when not in use.
Check out this comprehensive guide to reducing air leakage in your home.
Key Points
Air leakage is responsible for up to 30% of a building's heat loss.
Newer homes are built more airtight to reduce heating and cooling costs.
A home from the early 1900's may have total air leakage equal to a 50cm diameter hole in the wall.
Ventilation is important for air quality, but should be done in a controlled manner using specialized systems.
There are many small and simple things you can do to improve the airtightness of your home.