Air-tightness testing for UK homes explained

Air-tightness testing measures how much air leaks through a home’s fabric

Air-tightness testing, often called a blower-door test, uses a powerful fan mounted in an external door frame to depressurise your home and measure the volume of air flowing through gaps and cracks in the building fabric. The test result is expressed either as air changes per hour (ACH) or as air permeability in cubic metres per hour per square metre of envelope area (m³/(h·m²)) at a reference pressure of 50 Pascals. A lower number means a more airtight home, which typically wastes less heat through uncontrolled ventilation.

The direct answer is that a typical new UK home built to 2026 standards will have an air permeability target of 5 m³/(h·m²) at 50 Pa or better, and a standalone test costs between £200 and £350. The UK’s 2021 Part L of the Building Regulations requires new homes to achieve an air permeability of no more than 8 m³/(h·m²) at 50 Pa, though many new builds aim for 5 or lower (DESNZ, Approved Document L, 2021 edition with 2023 amendments, Section 4.2).

Air-tightness testing is the only reliable way to quantify how much heat you are losing through uncontrolled air leakage. The Energy Saving Trust notes that a typical detached home can reduce its heating bill by 10–20% by sealing the largest leaks identified during a test (Energy Saving Trust, Air tightness: a guide for householders, February 2022).

The test is mandatory for most new UK homes and major extensions

Building Regulations Part L, as enforced in 2026, require a completed air-tightness test for every new dwelling and for extensions where the glazing area exceeds 25% of the floor area. Homes built under the Future Homes Standard, which became mandatory in January 2025, must meet a target air permeability of 5 m³/(h·m²) at 50 Pa or better (DESNZ, Future Homes Standard: 2025 consultation response, December 2023).

A test is also required if a home is being retrofitted with new airtightness measures as part of a larger renovation project, for example under the ECO4 scheme. Ofgem’s ECO4 technical guidance specifies that air-tightness testing must be carried out before and after certain insulation measures to verify the improvement (Ofgem, ECO4: Technical requirements and guidance, Version 6, March 2026).

If you are planning a major extension or a new-build home, your building control body will require a test certificate before signing off the project. Without a passing test result, your home cannot receive a completion certificate under Building Regulations.

Eligibility for grants depends on your home’s age, location, and energy rating

The Great British Insulation Scheme (GBIS) and ECO4 offer free or subsidised air-tightness testing only for homes in Council Tax bands A–D in England, or bands A–E in Scotland and Wales, with an Energy Performance Certificate (EPC) rating of D, E, F, or G. Homes built before 2000 are the primary target for ECO4-funded testing; homes built after 2000 are generally excluded unless they have a very poor EPC rating (Ofgem, ECO4: Eligibility and referral guidance, Version 5, January 2026).

Grant eligibility is assessed by your energy supplier or a local authority through the LA Flex scheme. You cannot self-refer for a test under GBIS or ECO4; the scheme operator must determine that your home meets the criteria and that the test is part of a wider insulation measure. The Great British Insulation Scheme specifically requires that the test is carried out alongside a qualifying insulation measure such as loft or cavity wall insulation (GOV.UK, Great British Insulation Scheme: eligibility, updated February 2026).

For homeowners who do not meet these criteria, the only route to a subsidised test is through local authority discretionary schemes, which vary by council. how to check your EPC rating for free

Who does NOT qualify for a grant-funded air-tightness test

Homes already meeting an EPC rating of C or above are ineligible for any grant-funded testing under GBIS or ECO4. New-build homes completed after 2010 are also not eligible because they already meet Building Regulations standards and are considered sufficiently airtight (Ofgem, ECO4: Exclusions and exemptions, Version 4, September 2025).

Private landlords with a valid EPC rating of E or above may still qualify for testing under ECO4 if the property is in a low-income area, but only if the testing is part of a larger insulation measure such as external wall insulation. The Department for Energy Security and Net Zero guidance states that standalone air-tightness testing is not a qualifying measure under ECO4, it must be linked to a primary insulation improvement (DESNZ, Energy Company Obligation (ECO): scheme guidance, updated January 2026).

If your home falls into any of these excluded categories, you can still arrange a voluntary test privately, but you will pay the full market rate.

Quick numbers what a test costs and what it saves

These figures assume that air-tightness sealing is carried out alongside other insulation measures. Sealing alone, without adding insulation, will produce smaller savings and a longer payback period. The payback period also depends on your current heating fuel type and the severity of the leaks found.

How to confirm you need a test and how to find a certified tester

The only way to know for sure whether your home needs a test is to commission a blower-door test from an accredited company listed on the ATTMA (Air Tightness Testing and Measurement Association) register or the BSRIA (Building Services Research and Information Association) register. For Building Regulations compliance, your building control body will specify whether a test is required based on your project type.

For grant-funded testing, your energy supplier or LA Flex scheme will arrange the test through their own approved contractors. You cannot choose your own tester under GBIS or ECO4. For voluntary testing, such as before a home renovation or to improve your EPC rating, you must hire an ATTMA-registered tester who holds a BINDT (British Institute of Non-Destructive Testing) Level 1 or Level 2 certification for air-tightness testing (ATTMA, Find a tester, accessed 2026).

If you are testing for EPC improvement purposes, the test must be carried out by a certified assessor who is also registered with an accreditation scheme such as BSRIA. Results from non-certified testers will not be accepted by Building Control or for EPC purposes (BSRIA, Air tightness testing: certification and accreditation, 2025).

Installer certification what to check before hiring

For a grant-funded test, the installer carrying out the insulation measure must be MCS-certified for that specific measure, and the tester must be ATTMA-registered. The two roles are separate: the insulation installer and the air-tightness tester are usually different companies. You should verify both certifications before work begins.

For voluntary tests, the tester must hold a valid ATTMA membership and a BINDT Level 1 or Level 2 qualification in air-tightness testing. Do not hire a tester who is not on the ATTMA register. Results from non-registered testers are not accepted by Building Control or for EPC purposes, and you will have no recourse if the test is rejected (ATTMA, Certification requirements, 2026).

Building Regulations Approved Document L, Section 4.3, states that air-tightness testing must be carried out by a person with suitable training and experience, and that the test equipment must comply with the relevant British Standard (GOV.UK, Building Regulations: Approved Document L, 2021 edition, Section 4.3). For peace of mind, ask for the tester’s ATTMA membership number and BINDT certificate before booking. how to find an MCS-certified installer for your home