Some builders are concerned about making home too airtight Some arguments they give are:

1. “Humans need to breathe, and so does a building.”
2. “We don’t want occupants suffocating—fresh air has to come from somewhere.”
3. “If the building is too tight, we’ll need to install an HRV or ERV system.”
4. “If we’re relying on natural ventilation, why worry about air leakage?”
5. “We don’t want mould growing in our buildings.”

To begin with, these concerns stem from of lack of ventilation, not airtightness.  Air leakage is NOT ventilation. So lets get back to basics:

What is Ventilation?

Ventilation is the intentional introduction of outdoor air into a building, either through natural or mechanical means. In apartments or enclosed buildings, it’s also crucial to consult with a fire engineer and implement a pressure relief strategy for fire safety.

• Natural ventilation relies on open windows, vents, and other planned openings, driven by wind and temperature differences.

• Mechanical ventilation uses fans to deliberately supply or exhaust air.

For ventilation to be effective we need to consider the quantity, the quality, and the distribution of air into an occupied space. Can air leakage satisfy these three factors? Here’s why it falls short:

• Air from leaks is not filtered. It may come from a mouldy, dusty, or vermin-infested building cavity.
• There is no way to easily temper the air coming in, so it brings the temperature, humidity or dryness of the outside with it.
• Air leakage leaves you at the mercy of the weather. On windy, hot, or cold days, there is lots of air exchange. But on calm days there is almost none.
• Because you can’t locate or control all air leaks, it’s very hard to make sure each room gets the right amount of fresh air.

There is no way to compare air leakage with ventilation! Not only does infiltration fail to meet ventilation needs, but it also has additional harmful effects to your building and the health of its occupants.

Condensation and Mould Risk

When infiltration brings air from outside, it can create localised cold spots in walls, floors, and ceilings. These have the potential to create condensation, which can lead to mould growth or stains on finishes. Unchecked, condensation can lead to rotting or corrosion of materials, causing structural damage. It also makes a more inviting habitat for a termite infestation. Mould hidden inside walls can spread spores throughout the home and is nearly impossible to clean.

For buildings that are designed for natural ventilation, the openings should be fitted with condensate drains and be constructed using water-resistant materials. The location of these openings should be accessible for cleaning and maintenance. The most common example is mould that forms on leaky windows, which can be cleaned easily.

Reduced Insulation Performance

When insulation materials are rated in the laboratory, they are under controlled conditions with no air moving through the test sample. In the real world, air leaks can pass air through insulation, which substantially reduces insulation performance in two ways:

• Direct bypass – air leakage can pass right around both rigid and fibrous insulation
• Wind washing – air can pass through bulk insulation material itself, disturbing air pockets trapped by the fibres and stealing the heat it is meant to retain

Unwanted distribution of pollutants throughout the building

In leaky buildings, pollutants can distribute through a building via unintentional gaps and cracks. This can create problems ranging from minor nuisances such as odours to more serious issues such as carbon monoxide from a garage or car park. Most dangerously, they are a potential path of smoke in the case of a fire.

Other issues from air leakage

Air leakage in larger buildings can also contribute to noise infiltration and noise production from whistling under windy conditions. Lastly, any hole to the outside, garage, underground car parks or other unconditioned spaces serve as easy paths pollutants or unwanted pests. Sealing up these paths is the cheapest and first method of pest control.

To address concerns for airtightness in homes:

When someone says a house “needs to breathe,” ask them to breathe through their eyes. Sounds ridiculous, right? Humans breathe through their mouth or nose—designed for that purpose. Homes should do the same: breathe through designed ventilation systems.

Key points:

• You can’t make a home too airtight if you provide proper ventilation.

• For typical homes, mechanical ventilation can be simple and low-cost. A continuously running, remote-mounted exhaust fan is quiet and energy-efficient.

• Air should never come through walls—true fresh air should be filtered, controlled, and delivered where needed.

• To prevent mould and condensation, combine mechanical ventilation with thermal bridge control. Even uninsulated outdoor areas like carport soffits can grow mould, showing that moisture control is more complex than ventilation alone.