What is the purpose of an airtightness test (e.g., blower door test) in buildings?

• A. To measure air leakage and identify opportunities to improve energy efficiency and indoor air quality.
• B. To measure structural load capacity of walls.
• C. To assess acoustical performance of envelope.
• D. To determine thermal mass of interior finishes.

Answer: (A)

Air leakage through the building envelope is what an airtightness test quantifies. A blower door creates a controlled pressure difference across the shell and measures how much air leaks to determine the leakage rate. This information helps identify leaks and quantify energy losses, guiding sealing and insulation improvements to cut heating and cooling loads. Improved airtightness also supports better indoor air quality by reducing unintended drafts and the unplanned exchange of outdoor pollutants and moisture. The test is specifically about the envelope’s airtightness, not about structural load capacity, acoustical performance, or the thermal mass of interior finishes, which is why those aspects aren’t assessed by this test.