Dashpivot article page – Part L air tightness

Part L air tightness

Part L Air Tightness

Part L of the UK Building Regulations, which focuses on the conservation of fuel and power, places significant emphasis on air tightness in buildings.

Air tightness is a measure of how much uncontrolled air enters or leaves a building through leaks in its fabric.

It's an essential factor in the energy efficiency of a building, as poor air tightness leads to higher energy use for heating or cooling.

Importance of Air Tightness for Part L

Air tightness plays an important role in energy efficiency, as proper air sealing reduces heat loss in winter and heat gain in summer.

Lowering uncontrolled air leakage leads to reduced heating and cooling costs.

Improved air tightness enhances indoor comfort by minimizing drafts and cold spots.

Part L Requirements for Air Tightness

New buildings must undergo air permeability testing to demonstrate compliance. This test measures the amount of uncontrolled air leakage through gaps and cracks in the building fabric.

Part L sets specific targets for air permeability, expressed in terms of cubic meters per hour per square meter of envelope area at a given pressure (m³/h·m² @ 50 Pa). The allowable air permeability values may vary depending on the building type and the version of Part L being applied.

Buildings must be designed and constructed to minimise air leakage. This includes attention to continuous air barriers, sealing of penetrations, and appropriate detailing at joints and connections.

The maximum target for air tightness is <8m³/h·m²)@50Pa, which is a 2-point reduction from the current maximum of 10. This is going to drop again to <5m³/h·m²)@50Pa when The Future Homes and Buildings Standard comes into full effect in 2025.

< 8m³/ (h·m²) @ 50Pa

Part L Air tightness compliance and certification

Builders must provide evidence of compliance, including the results of air tightness testing. This can be coupled with a Part L Photographic Evidence report to show further proof of compliance.

Independent certification bodies often conduct the air tightness testing, ensuring impartiality and accuracy.

Compliance with air tightness requirements is a part of the building control approval process.

Air tightness challenges and considerations

While air tightness is crucial for energy efficiency, adequate ventilation is necessary for indoor air quality. Part L also addresses the need for controlled ventilation systems, particularly in tightly sealed buildings.

Alongside air tightness, minimising thermal bridging - where heat bypasses the insulation through conductive materials - is important for overall thermal performance.

Documenting Part L air tightness compliance

The first step in documenting air tightness is to plan for air permeability from the design stage. This involves ensuring that the building design incorporates features that minimise air leakage, such as continuous air barriers and proper sealing of penetrations. It's also important to choose materials and construction methods that support good air tightness.

Once the building is constructed, air tightness testing must be carried out by a qualified professional. This testing usually involves pressurising and depressurising the building and measuring the rate of air leakage. The results of this test are crucial for the documentation process.

The test results should be compiled into a comprehensive report. This report should detail the testing methodology, the conditions under which the test was performed, and the findings, including the measured air permeability rate. Photographic Evidence can be used to show compliance or non-conformance with Part L air tightness requirements. If the building fails to meet the required standards, the report should also include recommendations for remedial actions to improve air tightness.

It's also important to provide evidence of compliance with other related aspects of Part L, such as thermal bridging and ventilation. This can include details of the construction methods used, materials, and any specific design features that contribute to energy efficiency and indoor air quality.

In addition to the air tightness test report, builders should include a declaration of conformity, which is a statement that the construction has been carried out according to the approved design and complies with the relevant building regulations.

This documentation should be submitted to the relevant building control body as part of the overall compliance process for building regulations. It's important to keep copies of all documents for future reference, especially for any subsequent renovations or for selling the property.

See an example of a Part L Photographic Evidence report below, showing air tightness and thermal insulation, and customise it for your project needs.

Part L Photographic Evidence

Use this digital Part L Photographic Evidence template to show Part L air tightness compliance

Document Part L air tightness with a digital Photographic Evidence report

Breeze through compliance audits by coupling your compliance report with a Part L Photographic Evidence template.

Take photos of doors, insulation, or construction at different stages to show that work done matches the energy-efficient designs.

Add photo markup to photos taken to highlight adherence to Part L, or non-conformance of work that needs to be amended.

Customise the Photographic Evidence report with the drag and drop form builder to add any fields or sections you need to show Part L compliance.

Add digital signature sections to your documents to ensure easy compliance and signoff approval.

Create workflows for Part L air tightness compliance

Keep on top of your Part L requirements by using digital processes to plan, document and get sign off approval on air tightness and other Part L needs.

Use this Part L Photographic Evidence app to enable your team to take photos on site, add them to the report and fill out the rest of the report from the mobile or tablet.

Get automatic notifications when a planned report needs to be recorded, and when a completed report needs signoff approval before it can be marked as closed off.

Manage completed reports in Timeline view for a chronological list of reports grouped by date, or by Register view with a more detailed, spreadsheet-like view.

Share completed reports in a single click from the app to your team or to 3rd parties such as auditors as PDF or CSV.

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Über Nick Chernih

Nick is the Senior Marketing Manager at Sitemate. He wants more people in the Built World to see the potential of doing things a different way - just because things are done one way doesn't mean it's the best way for you.

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