Air Tightness – Why is it important?

One of the most overlooked conditions of homes is how air tight they are.  Both new and renovated buildings are prone to problems if high levels of air-tightness aren’t prioritized.  By ensuring that this detail is properly attended to, the results are healthy buildings, but even more importantly, healthy home owners.


An air tight home makes humidity management much easier.  Keeping Relative Humidity levels between 40%-60% in all seasons reduce a great number of health risks.  Here are the reasons why:

Too low (below 40%)

  • allows viruses and bacteria to travel and spread more easily.
  • increases throat irritation and chances of respiratory infection.
  • increases dust content, which invite more asthma symptoms.

Too high (above 60%)

  • increases risk of mould and fungus growth.
  • reduces bacterial resistance.
  • encourages dust mite reproduction.
E.M. Sterling, A. Arundel, and T.D. Sterling, Criteria for Human Exposure to Humidity in Occupied Buildings (ASHRAE Transactions, 1985), Vol. 91, Part 1

This doesn’t mean that these conditions will immediately occur if the humidity is temporarily outside the “zone”, but having an air-tight home makes maintaining these levels so much easier.


Radon gas is a highly radioactive gas that’s present in the soil of all areas of Canada.  It is the number one cause of lung cancer among non-smokers.  What’s strange is that in some houses there are dangerous amounts, but in the neighbour’s house there isn’t any.  Unfortunately, the leakier the house, the more infiltration.  This is because the constant flow of unregulated air comes through the basement walls and floor, unfortunately carrying Radon.

Moisture in the Wall

Leaks in air barrier allow air to flow through, bringing with it water vapour.  When this water vapour condenses within the wall assembly, it leaves water droplets.  This accumulates, leading to mould and mildew.  Not only is this not healthy for the homeowners, it also starts decay in the wall.

Ashleigh Uiska, M.Sc.Arch., AOCAD

Energy Efficiency

Increasing air tightness is the most effective way of increasing a building’s energy efficiency.  Even more effective than increasing insulation.  Think of insulation as a sweater.  A sweater keeps you hot and comfy when inside, but step outside on a cold, windy day and that wind will carry that coziness away in a hurry

Now put on a coat.  The windbreaking properties allow warmth to return. The effect of air leakage is immediate.  When the wind blows on a cold winter day, a leaky house will let that cold air in and leak the indoor warmth outside.  This is how the house works.  Sure… the heavier the “sweater” the warmer you’ll feel, but you must keep the air from blowing through. Stopping that air flow means keeping the warm air inside, and puts an end to you paying to heat the outdoors.

One more thing…  Whole-home ventilation is key.  Having continuous, balanced, and efficient fresh air delivery ensures that the owners of an air-tight home have healthy air to breathe.  A Heat Recovery Ventilator is the best way to make this happen.  Stale indoor air is exhausted to the outside and fresh outdoor air replaces it. 

Air-tight homes are healthy, comfortable and more energy efficient.  Contact us to learn more about how to Build it Better.

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We can’t wait to help you build the home you’ve always wanted. Contact Effect Home Builders today and find out how we build it better.

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