Airtightness (TG 27/2025)

Airtight buildings have reduced levels of air leakage. Air leakage, sometimes known as infiltration or draughts, is the uncontrolled flow of air through gaps and cracks in the fabric of a building.

Airtightness is one of the key components of assessing the performance of buildings. In conjunction with providing suitable ventilation, designing and construction buildings to be reasonably airtight can result in reduced energy use, improved occupant comfort and improved indoor air quality.

This topic guide explains the basics of airtightness: What is it? Why is it important? In what situations is airtightness testing required and how is it carried out? It is aimed at a general construction industry audience including engineers, site managers, and anyone involved in getting a building to pass its airtightness test. The focus is on regulations and standards that apply in the UK and Republic of Ireland, although the principles of airtightness testing apply all over the world.