Nearairtightness

Nearairtightness refers to a state where a building envelope has very few uncontrolled air leakages. It is a characteristic of a building that is designed and constructed to minimize the passage of air into and out of the interior spaces through gaps, cracks, and other openings in the building's shell. This includes elements such as walls, roofs, floors, windows, and doors. Achieving nearairtightness is a critical component of energy-efficient building design and construction.

A highly airtight building prevents conditioned air from escaping and unconditioned air from entering, which significantly reduces the energy required for heating and cooling. This tighter envelope also helps to improve indoor air quality by controlling the movement of pollutants, dust, and moisture. Furthermore, nearairtightness contributes to better thermal comfort for occupants by reducing drafts and maintaining more consistent indoor temperatures.

Measuring nearairtightness is typically done using a blower door test. This test depressurizes or pressurizes the building and quantifies the rate of air leakage. Standards and building codes often specify maximum allowable air leakage rates to ensure a certain level of energy performance and occupant comfort. While complete airtightness is practically impossible and undesirable due to ventilation needs, nearairtightness represents a desirable level of control over air infiltration and exfiltration.