Air-Tightness is defined as the resistance to inward or outward air leakage through unintentional leakage points or areas in the building envelope. An airtight building, when combined with an appropriate ventilation strategy will result in lower heating and cooling demands (due to reduced heat loss/gain); will require smaller heating and cooling equipment; will improve the performance of the ventilation system; will reduced the chance of mold and rot because moisture is less likely to enter and become trapped in cavities; and will result in fewer drafts, and thus, increased thermal comfort.

Air-Tightness is measured in Air Changes per Hour (ACH), which is determined by performing a Blower-Door Test, which calculates the volume of air being added to or removed from a building at a specific pressure (50 Pascals).

SUSTAINABLE.TO achieves superior air-tightness by paying extra attention too the application of a continuous air barrier, and making sure gaps are sealed where windows and doors meet walls.

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