In today’s environmentally conscious world, building homes that are energy-efficient isn’t just a choice—it’s a legal and environmental responsibility. One of the most critical aspects of ensuring a home meets modern energy standards in England is complying with Air tightness building regulations. These regulations are a central part of the UK’s wider strategy to reduce carbon emissions and improve energy performance in new and existing buildings.
In this guide, brought to you by HouseBuild, we’ll explain everything homeowners, builders, and developers need to know about air tightness building regulations in England, with a particular focus on Part L of the Building Regulations, which outlines the energy efficiency requirements for buildings.
What is Air Tightness and Why Does It Matter?
Air tightness refers to how effectively a building prevents uncontrolled air leakage through gaps and cracks in the building envelope. These leaks can significantly affect a home’s energy efficiency, causing heat loss in the winter and heat gain in the summer. Poor air tightness leads to:
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Increased energy bills
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Greater carbon emissions
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Uncomfortable indoor environments
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More strain on heating and cooling systems
That’s why air tightness building regulations are vital—they ensure buildings are constructed to limit air leakage, improving energy performance and comfort for residents.
Air Tightness and Part L of the Building Regulations
Part L of the Building Regulations in England sets the standards for energy efficiency in both domestic and non-domestic buildings. For dwellings, the relevant parts are:
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Approved Document L1A: New dwellings
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Approved Document L1B: Existing dwellings
Under Part L1A, new homes must achieve a certain level of air tightness, measured by the air permeability rate, usually expressed in m³/(h·m²) at 50 Pascals. The current target for new builds is an air permeability of ≤8.0 m³/(h·m²), but many developers aim for 5.0 or lower to meet overall energy performance targets.
This air tightness level must be verified through an air pressure test, often referred to as a blower door test, carried out by a certified professional.
Air Pressure Testing: What You Need to Know
Air pressure testing is a mandatory requirement for most new homes under Part L of the air tightness building regulations. Here’s how it works:
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Preparation: All doors, windows, and intentional ventilation openings are sealed.
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Testing: A calibrated fan is fitted into an external door opening and used to pressurise or depressurise the house.
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Measurement: The rate of air leakage is measured and calculated.
The result will determine whether your building complies with the legal air permeability limit. If it fails, remedial work is required before retesting.
At HouseBuild, we ensure that all our projects are tested and certified to meet or exceed these air tightness targets, ensuring our clients benefit from long-term energy efficiency and lower carbon emissions.
Design Strategies to Improve Air Tightness
Meeting the air tightness building regulations begins at the design stage. Here are proven strategies to help your project meet compliance:
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Continuous Air Barrier: Design a continuous line of airtight materials through walls, floors, and ceilings.
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Quality Sealing: Seal joints between materials and around service penetrations such as pipes and wires.
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High-Quality Materials: Use certified air barrier products, tapes, and membranes.
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Construction Supervision: Monitor site practices to prevent damage or gaps in the air barrier.
HouseBuild integrates these principles into every build, ensuring air tightness isn’t an afterthought but a core part of the building’s performance.
Common Air Leakage Points to Avoid
Understanding where air leaks commonly occur helps prevent them. Problem areas include:
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Gaps around windows and doors
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Wall-floor and wall-ceiling junctions
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Loft hatches and eaves
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Service penetrations (e.g., cables, pipes)
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Skirting boards and sockets
All these must be sealed correctly to comply with air tightness building regulations and ensure a successful air pressure test.
The Role of SAP Calculations in Air Tightness
The Standard Assessment Procedure (SAP) is used to calculate the energy performance of new homes. The air permeability rate achieved in the pressure test is a key input in SAP. A poor air tightness score will raise the dwelling emission rate (DER), possibly pushing it above the permitted target emission rate (TER).
Failing to meet the air tightness target could therefore mean failing the SAP assessment—and non-compliance with Part L of the building regulations.
At HouseBuild, we coordinate SAP assessments alongside air pressure testing to ensure a smooth path to compliance.
Do All Buildings Need Air Tightness Testing?
While most new builds are required to undergo air tightness testing, there are a few exemptions:
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Very small developments (less than 2 units), if a representative sample is tested
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Extensions to existing buildings
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Certain conversions (e.g., barn conversions may follow L1B)
Even where testing isn’t strictly required, following the air tightness building regulations is still highly recommended to improve comfort and reduce heating costs.
Consequences of Non-Compliance
Non-compliance with Part L and air tightness targets can have serious implications:
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Delays in project completion
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Increased construction costs due to remedial work
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Difficulty selling or renting the property
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Legal consequences and penalties
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Poor energy ratings, affecting long-term property value
At HouseBuild, we take compliance seriously. We provide expert design, construction supervision, and testing support to ensure your project not only meets but exceeds the expectations of modern regulations.
Final Thoughts: Building an Airtight Future with HouseBuild
Air tightness is a cornerstone of modern homebuilding and is central to achieving energy-efficient, low-carbon housing in the UK. As the government tightens regulations to meet climate goals, ensuring compliance with air tightness building regulations, especially Part L, is more important than ever.
Whether you’re a homeowner planning a self-build or a developer managing multiple plots, partnering with experienced professionals makes all the difference. At HouseBuild, we offer complete guidance, from design to testing, helping you create homes that are compliant, comfortable, and future-ready.
Need help with air tightness compliance?
Contact HouseBuild today to speak to our building regulation experts and discover how we can make your project energy-efficient and regulation-ready.
Visit www.housebuild.co.uk for more compliance guides, tips, and expert building services across the