Building Air-tightness

Airtightness is measured by ACH @ 50 Pa, ELA (Equivalent Leakage Area), & NLA (Normalized Leakage Area). The ACH is affected by the SV ratio (surface area to volume), air barrier system and location, building envelope, and any penetrations thru the building envelope.

Air changes per hour measure how much air leaks in and out of a building enclosure; commonly referred to as “air-leakage rate”. This is measured by determining how many time the air in the building changes over in 1 hour at 50 pascals of pressure. The lower the ACH the better as you want to rely on the ventilation system to provide fresh, filtered air to the home instead of pulling air through the walls, floors, and roof assemblies.

Min. ACH for BC Energy Step Code Levels

Step 3: 2.5 ACH              Step 4: 1.5 ACH              Step 5: 1.0 AC

ELA (equivalent leakage area) – This is based on in² or m² at 10 pascals of pressure. If you were to add up all the holes throughout the building envelope to get one hole.

NLA (normalized leakage area) – Is the ratio of the ELA to the exposed surface area of the building. This is a better metric for comparing the air leakage of different sized homes. Also based on in² or m² at 10 pascals of pressure.

Note: Air Tightness is the most cost-effective measure for creating an energy efficient building! 

Common air leakage paths

Wind can create pressure differences between the inside and outside of a building. Air infiltration and exfiltration through the building envelop can be reduced with a good air barrier system.