Ventilation & air leakage: different things

‘“Build tight; ventilate right” a common mantra chanted by building scientists.

One of the biggest areas of confusion when it comes to energy efficiency, thermal comfort, indoor air quality and moisture management is the difference between ventilation and air leakage. They are not the same thing.

Ventilation is a system for removing and replacing air; inside our homes it can include doors, openable windows, exhaust fans and other mechanical systems. Air leakage, on the other hand, is the result of building imperfections or gaps in the building’s envelopes.

The sub-floor, wall cavities and roof spaces of our homes (the interstitial spaces) also require some ventilation and this must be planned for and implemented well too.

Ventilation systems are ‘designed’: they result in controlled or planned air movement and exchange. Air leaks are the opposite: they are deviations from the design and create uncontrolled air movement that happens all the time.

Ventilation inside your home is controlled — by you. It can be as simple as opening windows to cross-ventilate your home naturally. We design our projects to have good, natural cross-ventilation. We also plan carefully to extract the moisture in wet areas to control humidity.

Air leakage is the constant, random stuff that’s happening due to permanent cracks and gaps in your home’s outer shell. It compromises your comfort, health and energy efficiency.

The air leaks in the internal envelope of our homes are responsible for the vast majority of moisture that makes its way into interstitial spaces where hidden condensation problems can cause major structural damage and create health problems. Read more about that in Jenny’s Renew article on Condensation Management.

You can also read up on on air leakage testing and a previous journal post: Gaps are no Good.