What is a common measurement used to determine a building’s airtightness?

Air changes per hour (ACH) is a widely recognized metric used to evaluate a building's airtightness. It measures how many times the total volume of air within a space is replaced with outside air in one hour. A lower ACH value indicates better airtightness, as it signifies that less unwanted air leakage occurs, which is crucial for maintaining energy efficiency, indoor air quality, and comfort.

The importance of assessing airtightness through ACH lies in its direct impact on heating and cooling costs, moisture control, and the comprehensive performance of the building envelope. In contrast, thermal resistance evaluates how well a material resists heat flow and is relevant to insulation effectiveness but does not specifically measure airtightness. Overall energy consumption reflects a building's energy usage but lacks specificity concerning air leakage. Sound transmission class (STC) pertains to sound insulation, which is unrelated to airtightness concerns. Thus, ACH is the most relevant and specific measurement for determining a building's airtightness.