Air Tightness Testing: A Guide for UK Developers
## What is Air Tightness Testing?
Air tightness testing (also known as air permeability testing or blower door testing) measures the total volume of air that leaks through a building's envelope. It is a critical component of demonstrating compliance with Building Regulations Part L (Conservation of Fuel and Power).
### Why is it Required?
As buildings become more energy-efficient, the focus has shifted from just adding insulation to ensuring the building fabric is airtight. Draughts and uncontrolled ventilation account for a significant proportion of heat loss in modern buildings.
A test is required for:
- New build residential dwellings
- New build commercial properties
- Large extensions or conversions (in some cases)
### How the Test Works
1. **Preparation:** All external doors and windows are closed. Internal doors remain open. Intentional ventilation (e.g., extractor fans, trickle vents) is temporarily sealed.
2. **The Blower Door:** A large fan is temporarily installed in an external doorway.
3. **Pressurisation:** The fan forces air into (or out of) the building, creating a pressure difference (usually 50 Pascals) between the inside and outside.
4. **Measurement:** The software measures the airflow required to maintain this pressure difference. The result is expressed as m³/(h.m²) @ 50Pa.
### Passing the Test
The target air permeability score is set during the design stage in your SAP calculations (for domestic) or SBEM calculations (for commercial). The building must meet or beat this target to pass.
Under the latest Part L regulations, the maximum allowable air permeability is 8.0 m³/(h.m²), but most modern SAP calculations require a score of between 3.0 and 5.0 to pass overall.
### Tips for Passing First Time
- **Seal around services:** Ensure all pipework and cables entering through the external walls are sealed with acoustic/intumescent mastic.
- **Skirting boards:** Seal the gap between the floor and the wall behind the skirting boards.
- **Windows and doors:** Ensure all seals are intact and units are correctly aligned.
- **Loft hatches:** Use a proprietary insulated and draught-stripped loft hatch.
[Book your air tightness test](/services/air-tightness) with Avorria for fast, reliable results.
Air tightness testing (also known as air permeability testing or blower door testing) measures the total volume of air that leaks through a building's envelope. It is a critical component of demonstrating compliance with Building Regulations Part L (Conservation of Fuel and Power).
### Why is it Required?
As buildings become more energy-efficient, the focus has shifted from just adding insulation to ensuring the building fabric is airtight. Draughts and uncontrolled ventilation account for a significant proportion of heat loss in modern buildings.
A test is required for:
- New build residential dwellings
- New build commercial properties
- Large extensions or conversions (in some cases)
### How the Test Works
1. **Preparation:** All external doors and windows are closed. Internal doors remain open. Intentional ventilation (e.g., extractor fans, trickle vents) is temporarily sealed.
2. **The Blower Door:** A large fan is temporarily installed in an external doorway.
3. **Pressurisation:** The fan forces air into (or out of) the building, creating a pressure difference (usually 50 Pascals) between the inside and outside.
4. **Measurement:** The software measures the airflow required to maintain this pressure difference. The result is expressed as m³/(h.m²) @ 50Pa.
### Passing the Test
The target air permeability score is set during the design stage in your SAP calculations (for domestic) or SBEM calculations (for commercial). The building must meet or beat this target to pass.
Under the latest Part L regulations, the maximum allowable air permeability is 8.0 m³/(h.m²), but most modern SAP calculations require a score of between 3.0 and 5.0 to pass overall.
### Tips for Passing First Time
- **Seal around services:** Ensure all pipework and cables entering through the external walls are sealed with acoustic/intumescent mastic.
- **Skirting boards:** Seal the gap between the floor and the wall behind the skirting boards.
- **Windows and doors:** Ensure all seals are intact and units are correctly aligned.
- **Loft hatches:** Use a proprietary insulated and draught-stripped loft hatch.
[Book your air tightness test](/services/air-tightness) with Avorria for fast, reliable results.