Build Comply
Air Tightness Technical Guide
Air Permeability Testing
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Technical Guide: Air Tightness
To comply with Approved Document Part L1 and L2 of the Building Regulations, ensuring your building is air tight is essential.
Likewise, this too is paramount in a retrofit project.
Air testing, also known as air tightness, air permeability or air leakage testing is required.
Air Testing assesses the level of conditioned (heated or cooled) air leakage. Basically this is known as infiltration, evidently felt as uncontrolled ventilation. By ensuring that the building meets or exceeds the air permeability rating specified in a design stage SAP or SBEM Calculation, Air Testing guarantees energy efficiency and performance.
Our testing is routinely carried out using a blower door. Following the methodology to ATTMA standards in line with CIBSE TM23 or ISO 9972:2015.
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Click here to find our Air Permeability Site Status Checklist covering common leakage area preparation and recommended sealing
Welcome to our comprehensive technical guide on air tightness testing. This guide is designed to provide you with a detailed understanding of air tightness, why it’s essential, how it’s tested, and what you can do to improve it in your residential or commercial buildings.
Air tightness, or the lack thereof, plays a significant role in the energy efficiency and overall comfort of a building. Understanding the principles of air tightness testing and how to address air leakage issues can lead to substantial energy savings and a more comfortable indoor environment.
Our technical guide covers a range of topics, from the basics of air tightness to interpreting test results, common issues, and practical solutions. Whether you’re a homeowner, builder, architect, or developer, this guide provides the knowledge you need to make informed decisions about air tightness in your building projects.
If you’re ready to dive into the world of air tightness testing, simply select the section that interests you most, or start from the beginning to gain a comprehensive understanding of this critical aspect of building performance.
Air Tightness Consultancy for as little as £295+VAT
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What is Air Tightness?
Airtightness in buildings refers to their ability to prevent uncontrolled air movement. It involves sealing gaps and cracks in the construction, such as around windows, doors, cables, and pipes. By doing so, warm air stays inside, and cold air is kept out, contributing to energy efficiency and comfort. Here’s why it matters:
Air Tightness Improves Energy Efficiency
Achieving a reasonable level of airtightness improves energy efficiency. Up to 40% of heat loss can occur due to uncontrolled ventilation through cracks and gaps.
Air Tightness Promotes Cost Savings
Reducing draughts and maintaining a constant temperature saves energy and money. Unwanted air leakage can be the largest component of energy wastage in buildings.
Air Tightness Health and Comfort Benefits
Airtightness creates healthier indoor environments. People spend 80-90% of their time indoors, so maintaining air quality matters.
Increase Durability with Air Tightness
Protecting building fabrics from moisture is essential. Bulk air movement can carry more moisture than vapor diffusion, leading to interstitial condensation.
Why is Air Tightness Necessary?
Air Tightness Testing is crucial for several reasons, especially in the context of Part L of the Building Regulations in England and Wales. Let’s explore why:
Energy Efficiency
Accurate testing establishes and minimises the infiltration rate of cold air into buildings and prevents heated air from escaping through gaps, holes, and cracks in the building fabric . By identifying and sealing these leaks, we improve energy efficiency and reduce heating bills.
Heat Loss Reduction
Air infiltration through gaps can contribute significantly to heat losses in older UK dwellings—up to one-third of total heat loss. Improving airtightness decreases space heating requirements, making homes more comfortable and cost-effective.
Regulatory Compliance
Part L of the Building Regulations sets standards for energy performance. Achieving reasonable airtightness levels is essential. For dwellings, the target pressure test result is no worse than
while best practice aims for less than
Retrofitting Homes
Even existing buildings adhere to minimum airtightness standards (such as those under Part L). PAS 2035:2019 allows testing before, during, or after installing energy efficiency measures
Learn more about domestic Air Tightness Testing and Retrofit over at BEE Homes.
The Air Tightness Test Process
Typically a test is carried out by a single engineer using a UKAS calibrated blower door system. The system is essentially a fan mounted within a canvas, that’s installed within an external door or window. The fan is controlled by a fan speed controller, and a number of tubes connected to a multi-channel manometer, which is read and inputted into a software to generate a result.
Generally during this time other trades can remain within the building so long as the external envelope remains closed (external doors and windows) and internal doors open.
Typically the test takes between twenty minutes to a couple of hours. However, this all depends of the size of the building, the test locations, the ability to create stable pressure in the building and unfortunately the controllable influence of the British weather.
Air Tightness Consultancy
Here at Building Compliance Testing we offer a range of consultancy services:
- Desktop drawing review
- Specifications
- Preliminary audits and tool-box talks
- Site inspections and reporting
- Shell and core testing
- Diagnostic testing
- Final ATTMA accredited pre-completion testing