Air Tightness
2024-04-13
Understanding air tightness in buildings: ACH measurements, standards from building codes to Passivhaus, and why it matters for energy efficiency.
The air-tightness of a building is defined as Air Changes per Hour. It represents how many times the air within any given space is replaced in an hour at an indoor-outdoor air pressure of 50 pascals.
ACH = (Outside Air Intake) (ft^3/minute) x 60 / Volume of Space (ft^3)
| ACH50 | Quality |
|---|---|
| 7.5 | Old Homes, Pre 1981 |
| 4.3 | Average Home (Ontario) |
| 3.5 | 2020 Building Code |
| 2.5 | Energy Start v12.6 |
| 1.5 | R-2000 Standard |
| 1.0 | Net Zero Ready |
| 0.6 | Passivhaus |
Source: ACH at a Glance
