Introduction to Air Tightness Testing

Air permeability — also referred to as air leakage or air tightness — describes the uncontrolled flow of air in and out of a building through gaps, cracks, and imperfections in the building envelope. The process of measuring this is called air tightness testing.

Air testing is a critical requirement under the Building Regulations in the UK. Uncontrolled air leakage in newly constructed or refurbished buildings wastes significant amounts of energy, as heated or cooled air escapes through the building fabric. By measuring and reducing air leakage, buildings can achieve lower carbon footprints, better energy ratings, and improved comfort for occupants.

Through the air tightness testing process, the volume of air leaking through the building fabric is quantified in a standardised, measurable way. The result is expressed as air permeability — measured in m³/(h·m²) at 50 Pascals — and must meet or improve upon the Design Air Permeability established in the project’s SAP or SBEM calculations.

Why Air Tightness Matters

• Reduces heat loss — improving energy efficiency and lowering running costs
• Reduces carbon emissions from the building, supporting UK net zero targets
• Improves acoustic performance by reducing sound transmission through the fabric
• Supports effective ventilation system operation
• Required by Part L of the Building Regulations for all new-build dwellings and commercial buildings