Commercial Air Tightness Testing Requirements: A Complete Guide

Commercial air tightness testing is a legal requirement for most new commercial buildings across the UK. It plays a vital role in demonstrating compliance with Approved Document L (Part L) of the Building Regulations, helping to ensure that buildings achieve modern standards for energy efficiency, carbon reduction, and overall operational performance.

Whether you’re developing a warehouse, office building, retail unit, school, healthcare facility, industrial unit, or another commercial property, you’ll usually need to prove that your building meets specified air permeability targets before Building Control will issue final approval.

This guide explains everything you need to know about commercial air tightness testing, including when testing is mandatory, what Part L requires, how to prepare successfully, and why achieving a good result benefits your business long after construction has finished.

What Is Commercial Air Tightness Testing?

Commercial air tightness testing, also known as air permeability testing or air pressure testing, measures the amount of uncontrolled air leakage through the external envelope of a building. Using specialist blower door equipment, engineers pressurise and depressurise the building to identify how much air escapes through unintended gaps and openings.

Every commercial building will experience some degree of air leakage. However, excessive leakage significantly reduces energy efficiency by allowing heated or cooled air to escape while permitting external air to enter the building. This forces heating, ventilation and air conditioning (HVAC) systems to work harder, increasing operational costs and reducing occupant comfort.

Poor air tightness can result in:

• Higher heating and cooling costs
• Increased carbon emissions
• Difficulty complying with Part L Building Regulations
• Poor energy performance and EPC ratings
• Draughts and uncomfortable internal environments
• Reduced overall building performance

Many leakage paths are hidden behind finishes or located at complex construction junctions. Common examples include poorly sealed service penetrations, cladding interfaces, structural steel connections, door thresholds and roof junctions. Identifying and addressing these issues early can significantly improve a building’s overall performance and reduce the likelihood of failing the final compliance test.

When Is Commercial Air Tightness Testing Mandatory?

Under Approved Document L2, air tightness testing is mandatory for most newly constructed commercial buildings.

Testing is generally required for:

• All new commercial buildings with a floor area greater than 500 m²
• Large commercial extensions
• Major refurbishments where substantial alterations have been made to the building envelope
• Buildings where Building Control specifically requests verification of air permeability

Even commercial buildings below 500 m² may still require testing if it forms part of the approved energy assessment or Building Control considers it necessary.

The air tightness certificate produced after testing forms an essential part of the Building Regulations compliance package. Without satisfactory results, final sign-off may be delayed until remedial work has been completed and the building successfully retested.

For developers, contractors and project managers, this makes early planning essential. Leaving air tightness until the end of a project often leads to unnecessary delays, additional costs and programme disruption.

Understanding Part L Air Tightness Requirements

Approved Document L establishes the minimum energy efficiency standards for commercial buildings in England. Air tightness forms one of the key performance criteria used to demonstrate compliance.

1. Target Emission Rate (TER)

The building must achieve a calculated carbon emission rate that does not exceed the Target Emission Rate (TER). Excessive air leakage increases heating demand and can make it difficult to satisfy this requirement.

2. Air Permeability Target

Most commercial developments are designed to achieve an air permeability of 10 m³/h·m² at 50 Pascals (Pa) or better.

However, many projects specify significantly lower targets to improve energy efficiency or satisfy sustainability objectives such as BREEAM certification. Modern office buildings, schools and public sector developments frequently require much tighter envelopes than the minimum regulatory standard.

3. Demonstrating Compliance

Once testing has been completed, a formal air tightness test certificate must be submitted to Building Control as evidence that the completed building meets its design specification.

If the measured air permeability exceeds the design target, remedial sealing works will normally be required before the building can be retested.

4. Competent Testing

Testing should only be undertaken by suitably qualified and accredited organisations using calibrated equipment and recognised industry procedures. Selecting an experienced testing provider helps ensure accurate results while providing valuable guidance should remedial works become necessary.

Why Commercial Buildings Fail Air Tightness Tests

Many commercial buildings fail not because of one major defect, but due to hundreds of small leakage paths spread throughout the building envelope.

Some of the most common areas where air leakage occurs include:

• Roller shutter doors
• Loading bay doors
• Service penetrations for ducts, pipes and electrical cables
• Curtain walling interfaces
• Cladding joints
• Structural steel connections
• Roof-to-wall junctions
• Lift shafts
• Mechanical risers
• Door thresholds
• Expansion joints
• Ceiling void penetrations

On large commercial projects, coordination between multiple trades is often the biggest challenge. Electrical contractors, mechanical installers, cladding specialists and drylining contractors all create penetrations through the building envelope, and unless these are correctly sealed, they become significant sources of unwanted air leakage.

Early quality inspections during construction can dramatically reduce the likelihood of discovering problems during the final test.

Preparing for a Successful Air Tightness Test

Good preparation is one of the most effective ways to achieve a first-time pass and avoid costly delays.

Before the test takes place, contractors should ensure that:

• All external doors and windows are fully installed and operational.
• Service penetrations are permanently sealed.
• Internal finishes affecting the building envelope are complete.
• Trickle vents are closed where appropriate.
• Mechanical ventilation systems are switched off or temporarily sealed in accordance with testing procedures.
• Roof hatches, access panels and external openings are properly secured.
• Temporary construction openings have been permanently closed.

For larger or more complex developments, arranging a pre-test inspection can identify potential issues before formal compliance testing begins. This proactive approach often saves significant time and money by highlighting leakage areas while they remain easy to access.

Where buildings fail initial testing, diagnostic techniques such as smoke tracing and thermal imaging can quickly pinpoint leakage paths, allowing contractors to target remedial works rather than relying on trial and error.

The Benefits of Good Air Tightness

Although air tightness testing is a regulatory requirement, the benefits extend far beyond simply obtaining Building Control approval.

A well-sealed commercial building offers significant long-term advantages, including:

Reduced Energy Costs

Heating and cooling systems operate far more efficiently when conditioned air remains inside the building. Lower energy consumption translates directly into reduced operating costs throughout the building’s life.

Improved Occupant Comfort

Reduced draughts create more consistent internal temperatures, improving comfort for employees, customers and building users.

Better EPC Ratings

Improved air tightness contributes to stronger energy performance calculations, helping buildings achieve higher EPC ratings and supporting sustainability objectives.

Lower Carbon Emissions

Reduced energy demand leads directly to lower carbon emissions, helping organisations meet environmental targets and future-proof their property portfolios.

Faster Regulatory Approval

Passing the air tightness test first time avoids delays with Building Control sign-off and helps projects remain on programme.

Increased Asset Value

Buildings with better energy performance are increasingly attractive to occupiers, investors and institutional landlords. Strong environmental performance can enhance rental value while reducing long-term operational expenditure.

As energy prices continue to rise and environmental legislation becomes more demanding, achieving excellent air tightness has become both a compliance requirement and a valuable commercial investment.

Accredited Expertise You Can Trust

Selecting an experienced, accredited testing provider is essential to achieving reliable, repeatable and fully compliant results.

APT Sound Testing is a UKAS-accredited ISO/IEC 17025 testing laboratory specialising in on-site air tightness testing for commercial and large-scale buildings. UKAS accreditation demonstrates that our testing procedures, reporting systems and quality management processes meet the highest recognised technical standards within the UK.

We are also an ATTMA Level 2 Registered Organisation, qualified to undertake testing on Large, Complicated and High-Rise (LCHR) buildings, including phased developments and zonal handovers. In addition, our ATTMA EA accreditation enables us to produce accurate envelope area calculations for complex commercial structures.

With more than 20 years of specialist industry experience, our engineers have successfully delivered testing and consultancy services on some of the UK’s most prestigious and technically demanding developments, including Battersea Power Station and the Imperial War Museum London.

Our combination of accredited competence, advanced testing equipment and practical construction experience allows us to deliver dependable results while helping clients achieve compliance as efficiently as possible.

Book Your Commercial Air Tightness Test

Commercial air tightness testing should never be viewed as a final hurdle at the end of construction. When planned correctly and supported by experienced specialists, it becomes an integral part of delivering an energy-efficient, compliant and high-performing commercial building.

APT Sound Testing provides nationwide commercial air tightness testing using the latest UKAS-calibrated modular blower door systems. We test everything from small commercial units to large warehouses, schools, offices, healthcare facilities and complex multi-storey developments.

Our engineers also provide advanced diagnostic services, including smoke tracing and thermal imaging, enabling us to quickly identify air leakage paths and support remedial works where required. This proactive approach helps maximise the likelihood of achieving a first-time pass while keeping projects on schedule.

If you’re planning a new commercial development or require testing for an existing project, our experienced team is ready to help.

Contact APT Sound Testing today by emailing info@aptsoundtesting.co.uk or call our friendly team on 07775 623464 to arrange your commercial air tightness test and ensure full compliance with UK Building Regulations.

BREEAM Indoor Air Quality Testing – Why It Matters

When it comes to creating healthy, comfortable buildings, indoor air quality is just as important as energy efficiency or acoustic performance. That’s why BREEAM places such a strong focus on ensuring the air inside a building is safe for the people who use it every day.

At APT Sound Testing, we’ve been carrying out BREEAM Indoor Air Quality (IAQ) testing for many years, helping developers, contractors, architects, and project managers achieve valuable BREEAM credits while ensuring buildings meet the highest standards of indoor environmental quality.

Whether you need an Indoor Air Quality Plan, post-construction air quality testing, or expert advice throughout your project, our experienced team is here to make the process straightforward from start to finish.

What is BREEAM Indoor Air Quality Testing?

BREEAM Indoor Air Quality Testing is designed to assess the quality of the air within a newly completed building before it is occupied. The aim is simple – to minimise harmful pollutants and create healthier indoor environments for future occupants.

As part of the assessment, we test for key airborne contaminants, including:

• Total Volatile Organic Compounds (TVOCs)
• Formaldehyde

If required, we can also test for additional pollutants depending on your project’s specific requirements.

The Two Stages of BREEAM Hea02

To achieve the available BREEAM credits under the Hea02 category, there are two important stages.

Stage 1 – Indoor Air Quality Plan (IAQP)

The first step is producing an Indoor Air Quality Plan during the design stage of your project.

This plan helps reduce the risk of poor indoor air quality by considering factors such as ventilation strategies, construction methods, building materials, and future maintenance. By identifying potential sources of contamination early, your project can be designed to provide a healthier environment for everyone who will use the building.

Our bespoke Indoor Air Quality Plans typically include:

• Advice on identifying and removing contamination sources
• Recommendations for controlling and diluting airborne pollutants
• Pre-occupancy flush-out procedures
• A practical checklist to prepare for third-party testing
• Guidance on maintaining good indoor air quality after occupation
• Independent testing and analysis

Stage 2 – Post-Construction Indoor Air Quality Testing

Once construction is complete and the building’s HVAC system is fully operational, it’s time for the post-construction Indoor Air Quality Test.

During our site visit, we collect air samples from representative occupied spaces, such as offices, classrooms, healthcare facilities, apartments, or other regularly occupied rooms.

The samples are analysed to measure pollutant levels against the limits specified by BREEAM. If any readings exceed the required thresholds, we’ll explain the findings clearly and recommend practical steps to help bring the building into compliance.

Why Choose APT Sound Testing?

We’ve helped clients across the UK successfully achieve BREEAM, Home Quality Mark (HQM), and other environmental compliance standards through reliable, accurate Indoor Air Quality Testing.

When you work with APT Sound Testing, you can expect:

• Experienced, qualified testing engineers
• Fixed, competitive quotations with no hidden surprises
• Helpful pre-test guidance to maximise the chances of success
• Testing carried out strictly in accordance with BREEAM Hea02 requirements
• Fast, clear reporting and expert technical advice

We understand that preparation is often the key to achieving compliance, which is why we’re always happy to provide practical advice before we even arrive on site.

Preparing for Your Air Quality Test

A successful Indoor Air Quality Test starts with good preparation. Our team provides a comprehensive checklist to ensure your building is ready before testing begins, helping to avoid unnecessary delays or repeat visits.

If you’re planning a BREEAM assessment, we’d be happy to provide our Indoor Air Quality Testing Checklist to help your project stay on track.

Need BREEAM Indoor Air Quality Testing?

If you’re looking for a trusted partner to carry out your BREEAM Indoor Air Quality Testing, APT Sound Testing is here to help.

From creating your Indoor Air Quality Plan to completing post-construction testing and reporting, we’ll guide you through every stage of the process with friendly advice and professional support.

Get in touch with our team today on 01525 303905 or email info@aptsoundtesting.co.uk to discuss your project. Alternatively, visit our Contact page to request a quotation.

Expert Air Tightness Testing Across the UK

APT Sound Testing provides professional Air Tightness Testing services throughout the United Kingdom, supporting projects of all sizes — from individual residential properties to large-scale commercial developments.

As one of the few companies in the UK accredited by UKAS to undertake both Air and Sound Testing, we provide a complete testing solution that helps clients achieve Building Regulations compliance efficiently. Our experienced engineers can complete Air Tightness, Sound Insulation and Ventilation Testing packages during the same visit, improving site coordination while reducing costs.

Unlike many testing companies, we do not subcontract our work. Every project is completed by our own highly skilled and accredited engineers, ensuring consistent quality, reliability and expert advice from start to finish.

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Why is Air Tightness Testing Required?

Air Tightness Testing became a legal requirement in England and Wales in 2006 under Building Regulations Part L, which focuses on the conservation of fuel and power.

Today, airtightness testing plays an increasingly important role in creating energy-efficient, low-carbon buildings. Poor airtightness allows uncontrolled air leakage through gaps and cracks in the building fabric, resulting in unnecessary heat loss, increased energy consumption and higher carbon emissions.

Building Regulations define air leakage as the uncontrolled movement of air through the gaps and openings within a building’s structure. In everyday terms, this is what we commonly experience as draughts.

By reducing unwanted air leakage, buildings can retain heat more effectively, improve energy performance and provide a more comfortable environment for occupants.

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Understanding Air Leakage Rates and Building Performance

When energy is lost through uncontrolled air movement, it contributes to the building’s overall emission rate. New developments must achieve specific air leakage targets to comply with Building Regulations.

For a typical residential property, the target air permeability rate is often around:

5.0m³/hr/m²

For commercial buildings, requirements are usually more demanding, with target rates commonly around:

3.0m³/hr/m² or lower

Achieving these targets requires careful consideration of the building’s air barrier from the early design stage through to construction completion.

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The Risks of Poor Airtightness

Air leakage affects buildings throughout the year.

Where air enters a building through uncontrolled gaps (infiltration), air usually escapes elsewhere (exfiltration). These unwanted air movements can create a number of problems:

Increased Energy Costs

Air leaking from a building envelope causes additional energy demand because replacement air must be heated or cooled. Air Tightness Testing helps identify leakage rates, allowing designers and building owners to better understand energy performance and optimise heating and cooling systems.

Condensation, Damp and Mould Problems

In winter, warm moist indoor air can escape through gaps in the building fabric and enter colder areas such as wall cavities and roof spaces. This can lead to condensation, mould growth and, over time, timber decay or structural damage.

Reduced Occupant Comfort

Draughts can significantly affect the comfort of people using a building. Cold air entering offices, homes or commercial spaces can create uncomfortable conditions and reduce occupant satisfaction.

APT Sound Testing has investigated buildings where excessive air leakage caused serious workplace comfort issues. In one case, a building recorded an air leakage rate of 25m³/hr/m². After leakage paths were identified and remedial works completed, the building achieved a result below 5m³/hr/m², significantly improving performance.

Increased Risk of External Pollutants Entering Buildings

Uncontrolled air leakage can also allow pollutants from outside to enter a building, including emissions from nearby roads, fuel stations, waste areas, restaurants and other external sources.

A well-designed and properly installed air barrier helps control airflow, improve indoor air quality and reduce the risk of unwanted pollutants entering occupied spaces.

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How Does Air Tightness Testing Work?

Air Tightness Testing is commonly carried out using a blower door test.

During the test, specialist equipment measures:

• The amount of air moving into or out of the building
• The pressure difference across the building envelope
• The overall air leakage rate

Where leakage is detected, our engineers can use techniques such as smoke testing to accurately locate air leakage paths.

Many buildings do not fail because of one obvious opening; instead, the main issues are often caused by multiple smaller gaps throughout the construction. Identifying these areas early allows corrective action to be taken before final compliance testing.

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Air Tightness Consultancy and Design Support

APT Sound Testing provides expert air tightness consultancy from the earliest design stages through to final completion testing.

Our team works with architects, developers, contractors and building professionals to help:

• Review building designs and air barrier strategies
• Identify potential leakage risks
• Provide guidance during construction
• Reduce the likelihood of failed air tests
• Achieve Building Control approval

As air tightness targets continue to become more demanding, early consideration of the building’s air leakage line is essential.

By working with us throughout the design and construction process, we can help ensure that airtightness requirements are achieved efficiently and cost-effectively.

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Combined Air and Sound Testing Packages

Many of our clients choose our combined testing packages because our engineers are accredited to carry out both Air Tightness and Sound Testing.

Our multi-skilled team allows multiple compliance tests to be completed during one coordinated visit, providing:

• Reduced project costs
• Improved site scheduling
• Less disruption for contractors
• Faster completion of compliance requirements

We can also provide out-of-hours testing, including weekend appointments, to minimise disruption to working sites and occupied buildings.

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Preparing for Your Air Tightness Test

To achieve a successful result, preparation is essential.

We recommend that developers and contractors consider airtightness requirements early and ensure that all elements of the air barrier are correctly installed before testing.

Our team can provide advice and guidance throughout your project, and we offer an air tightness checklist to help you prepare for your test.

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Why Choose APT Sound Testing?

APT Sound Testing has extensive experience delivering successful air tightness tests across London and throughout the UK.

Our team understands the requirements of Approved Document L and has completed thousands of tests across a wide range of residential and commercial developments.

With expert advice, UKAS accreditation and a commitment to quality, we help clients achieve compliance while improving the energy efficiency and performance of their buildings.

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Contact APT Sound Testing

If you need professional Air Tightness Testing, consultancy or compliance support, our experienced team is ready to help.

📞 01525 303905
📧 info@aptsoundtesting.co.uk

Contact APT Sound Testing today to discuss your project requirements and discover how our specialist air testing services can help you achieve compliance and improve building performance.

Common Air Leakage Paths: PAS 2035 Air Tightness Testing

One of the key observations from our extensive experience in air tightness testing is that the more complete a development is at the time of testing, the more likely it is to achieve a low air leakage result.

To help our clients prepare, we provide a comprehensive Air Leakage Checklist alongside every quotation. By engaging with projects throughout the retrofit process, we can offer practical advice and guidance on the most effective ways to minimise air leakage and achieve PAS 2035 Compliance first time.

Most Common Air Leakage Paths We Identify

During air tightness and smoke leakage testing, we frequently identify air leakage from:

• Poorly installed windows and doors that do not seal correctly against frames
• Missing or damaged window and door seals
• Faulty or damaged trickle vents
• Gaps at wall and skirting board junctions
• Gaps through existing floorboards on all levels
• Perimeter and internal wall-to-floor junctions
• Service penetrations for electrical, plumbing and mechanical installations
• Ceiling voids connecting to masonry cavity walls
• Eaves and roof cavity pathways
• Gaps around window sills and door reveals
• Bathroom and WC service penetrations
• Kitchen and utility service penetrations
• Gaps between dry lining systems and ceilings
• Unsealed chimneys and fireplaces
• Electrical, data and IT installations
• Loft hatches and access panels
• Ventilation penetrations through walls, roofs and ceilings
• Poorly installed extractor fans in kitchens, utilities and bathrooms

Failed an Air Tightness Test?

If your building doesn’t achieve the required result, there is no need to panic.

Our smoke leakage testing service can accurately identify the source of air leakage throughout the building envelope. We provide a detailed smoke survey report, allowing your team to carry out targeted remedial sealing works before retesting.

How We Can Help

APT Sound Testing has extensive experience supporting PAS 2035 retrofit projects and helping clients achieve compliance with Approved Document L and air tightness requirements.

As a UKAS-accredited ISO/IEC 17025 testing laboratory, we specialise in on-site air tightness testing for commercial and large-scale developments. We are also an ATTMA Level 2 registered organisation, qualified to test Large, Complex and High-Rise (LCHR) buildings, as well as phased and zonal handover projects.

Using the latest UKAS-calibrated Retrotec blower door equipment, our engineers have successfully delivered thousands of air tightness tests across the UK, including landmark developments such as Battersea Power Station and the Imperial War Museum London.

Our combination of accredited competence, technical expertise and over 20 years of industry experience ensures reliable, repeatable and fully compliant testing on every project.

📞 Need help preparing for your PAS 2035 air tightness test?

Preparing for your PAS 2035 air tightness test? Contact the APT Team on 01525 303905 or email info@aptsoundtesting.co.uk to discuss your project and avoid costly delays or test failures.

APT Sound Testing: the Leading Choice for Commercial Air Tightness Testing on Large Buildings

Airtightness has become one of the most important performance metrics in modern commercial construction. As the UK tightens energy‑efficiency requirements under Approved Document L and pushes toward net‑zero targets, developers and contractors must ensure their buildings achieve low air‑leakage rates, reduced heat loss, and long‑term operational efficiency.

APT Sound Testing Ltd has established itself as one of the UK’s leading specialists in commercial air tightness testing, particularly for large and complex buildings. With UKAS accreditation, ATTMA Level 2 certification, advanced multi‑fan blower door systems, and integrated diagnostic tools such as smoke testing and thermal imaging, APT delivers a level of accuracy and insight that few companies can match.

This article explores why APT Sound Testing is the preferred partner for commercial clients—and how their combined testing methodology helps buildings achieve compliance first time.

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The Importance of Airtightness in Commercial Buildings

Air leakage is one of the biggest contributors to heat loss in commercial buildings. Uncontrolled infiltration can account for 20–40% of total heating demand, especially in older or poorly sealed structures. APT’s blog Measuring the Air Tightness of Buildings explains how leakage affects energy performance and why accurate testing is essential:

Reducing leakage from 12–15 m³/hr/m² to below 5 m³/hr/m² can save thousands of pounds annually in heating costs. For large buildings, the financial and environmental benefits are even greater.

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High‑Power Multi‑Fan Blower Door Testing for Large Buildings

APT Sound Testing is one of the few UK companies equipped with six‑fan blower door systems, enabling them to test buildings over 10,000 m² in a single setup. This capability is essential for:

• Warehouses and logistics hubs
• Hospitals and healthcare facilities
• Schools and universities
• Office buildings
• Mixed‑use developments

Their blog Our Air Tightness Testing Procedure provides a detailed breakdown of the testing process, including pressure steps, equipment, and compliance requirements:

Using high‑power multi‑fan systems ensures:

• Faster testing
• Minimal disruption
• Highly accurate results
• Full compliance with ATTMA TSL2 and Building Regulations

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Smoke Testing: Visual Identification of Leakage Paths

While blower door testing quantifies leakage, smoke testing reveals it visually. APT uses small and large scale smoke machines to show exactly where air is escaping or entering the building envelope.

This method is particularly effective for identifying leakage around:

• Raised access floors
• Suspended ceilings
• Service penetrations
• Door sets and lobbies
• Roof junctions
• Wet rooms and plant areas

APT’s blog The Importance of Air Tightness Testing highlights how smoke testing provides immediate clarity for site teams, enabling targeted remedial sealing:

This reduces guesswork and increases the likelihood of passing the final compliance test on the first attempt.

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Thermal Imaging: The Most Powerful Diagnostic Tool for Hidden Defects

APT’s thermal imaging surveys are carried out by Level 2 and Level 3 certified thermographers using high‑resolution FLIR cameras. Thermal imaging is essential for identifying:

• Missing or damaged insulation
• Cold bridging
• Hidden air leakage
• Moisture ingress
• Poor thermal comfort
• Mould and condensation risks

When combined with blower door depressurisation, thermal imaging becomes even more effective. Cold external air entering the building appears as clear thermal signatures, revealing:

• Poorly sealed windows and doors
• Leaking service penetrations
• Defective roof/wall junctions
• Gaps behind cladding or drylining

APT’s blog Residential Air Tightness Testing– Q&A explains how thermal imaging can uncover issues that would otherwise remain invisible:

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Why APT’s Combined Approach Delivers the Best Results

APT Sound Testing’s integrated methodology, blower door testing + smoke testing + thermal imaging, provides a complete picture of a building’s airtightness.

This combined approach ensures:

• No leakage path is missed
• Hidden defects are exposed
• Contractors receive clear, actionable guidance
• Remedial works are targeted and efficient
• Compliance is achieved faster

Their blog Air Tightness Testing for PAS2035 reinforces how diagnostic‑rich testing supports both compliance and long‑term building performance:

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Regulatory Compliance and BREEAM Benefits

APT’s testing approach aligns with:

• Approved Document L2A – New non‑dwellings
• Approved Document L2B – Existing non‑dwellings

Thermal imaging also contributes to BREEAM credits, making it a valuable tool for sustainable building certification.

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Why Commercial Clients Choose APT Sound Testing Ltd

UKAS Accredited Testing

Ensures full compliance with Building Regulations and industry standards.

Expertise in Large and Complex Buildings

Engineers are ATTMA Level 2 certified and highly experienced in large‑scale commercial testing.

Advanced Diagnostic Capability

Few companies offer integrated blower door, smoke, and thermal imaging surveys at this level.

Fast Reporting and Clear Contractor Guidance

Reports are designed for site teams—clear, actionable, and technically robust.

Nationwide Coverage

APT can respond quickly to projects across the UK.

Over 22 Years of Experience

A long‑established specialist with a proven track record.

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Conclusion: APT Delivers Compliance, Efficiency, and Long‑Term Value

For developers, contractors, and building owners, airtightness is not just a compliance checkbox, it is a long‑term investment in energy performance, operational efficiency, and occupant wellbeing.

APT Sound Testing Ltd stands out because they don’t just test buildings, they diagnose, explain, and solve airtightness problems. Their integrated approach, advanced equipment, and highly trained engineers make them one of the UK’s leading providers for large‑scale commercial air testing.

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Contact APT Sound Testing Ltd

If you would like to arrange commercial air tightness testing, smoke testing, or thermal imaging for your project, APT Sound Testing Ltd offers nationwide coverage and rapid response times.

APT Sound Testing Ltd
Phone: 07775 623464
Email: info@aptsoundtesting.co.uk
Website: https://aptsoundtesting.co.uk

For more technical guidance, case studies, and insights, visit the APT Sound Testing blog: https://aptsoundtesting.co.uk/blog/

High-Capacity Air Tightness Testing for Buildings Over 10,000 m²

As building regulations tighten and energy performance standards continue to rise, airtightness testing has become a critical part of modern construction. For large commercial and industrial developments, achieving compliance is no longer just about meeting regulations — it’s about improving long-term efficiency, reducing operational costs, and ensuring high-quality construction standards.

However, testing very large buildings requires far more than standard equipment and basic experience.

APT Sound Testing is one of the few specialist companies in the UK with the capability to carry out air pressure testing on buildings exceeding 10,000 m². Backed by a high-powered 6-fan blower door system, Level 2 ATTMA registration, and UKAS accreditation, we provide reliable, accurate, and fully compliant airtightness testing for even the most complex projects.

Specialist Equipment for Very Large Buildings

Most air tightness testing companies operate with one or two fans, which is generally sufficient for residential properties and smaller commercial units. Large-scale developments, however, demand significantly greater airflow and testing capacity.

APT Sound Testing has invested in an advanced multi-fan blower door system specifically designed for testing large-volume buildings, including:

• Warehouses and logistics centres
• Supermarkets and large retail developments
• Schools, hospitals, and public sector buildings
• Multi-storey residential developments
• Industrial and manufacturing facilities
• Buildings with complex internal zoning

Our high-capacity system allows us to maintain stable test pressures across vast internal spaces while delivering highly accurate results. This not only ensures compliance with ATTMA TSL1, TSL2, and Part L requirements, but also reduces testing time and minimises disruption to construction programmes.

For buildings over 10,000 m², this level of capability is essential — and still relatively rare within the industry.

Why Accreditation Matters

Large-scale airtightness testing is not simply about using larger fans. It requires technical expertise, precise procedures, and recognised accreditation to ensure results are accepted by Building Control and project stakeholders.

APT Sound Testing is:

• Level 2 ATTMA Registered — authorised to test large, complex, and multi-zone buildings
• UKAS Accredited — providing independently verified testing procedures and traceable results

This gives contractors, developers, and consultants complete confidence that testing is carried out to the highest industry standards.

Our accreditation helps clients achieve:

• Compliance with Building Regulations Part L
• Acceptance by Building Control and warranty providers
• Support for BREEAM and sustainability targets
• Reduced risk of costly retesting or project delays

For large and high-value developments, using an accredited testing provider is essential to avoid unnecessary complications later in the programme.

Advanced Air Leakage Diagnostic Surveys

Achieving airtightness on large buildings can be challenging. Minor defects repeated across thousands of square metres can quickly lead to significant leakage rates.

To help identify and resolve problems efficiently, APT Sound Testing provides detailed air leakage diagnostic surveys using advanced testing methods.

Smoke Testing

Under pressurised conditions, smoke testing visually identifies leakage paths throughout the building envelope, including:

• Cladding interface failures
• Poorly sealed service penetrations
• Faulty window and door seals
• Roof-to-wall junction leakage
• Hidden construction gaps and voids

This allows contractors to pinpoint issues quickly and carry out targeted remedial works.

Thermal Imaging Surveys

Thermal imaging inspections are another highly effective diagnostic tool, especially when combined with depressurisation testing.

Thermal imaging can identify:

• Cold air infiltration
• Missing or poorly installed insulation
• Thermal bridging
• Hidden air leakage not visible during visual inspections

These surveys provide valuable insight into both airtightness performance and overall building envelope quality.

Detailed Leakage Reporting

APT Sound Testing provides comprehensive reports designed to help site teams resolve issues quickly and efficiently.

Our reports include:

• Annotated photographs and thermal images
• Leakage severity assessments
• Root-cause analysis
• Recommended remedial actions
• Prioritised sealing guidance

This structured approach helps contractors achieve compliance faster while avoiding unnecessary remedial costs.

Why Large Buildings Need Specialist Testing

Testing a building over 10,000 m² is fundamentally different from testing smaller properties. It requires:

• High-capacity blower door systems
• Advanced airflow measurement
• Multi-zone testing strategies
• Experienced engineers
• Robust diagnostic procedures
• Accredited reporting methods

Without the correct expertise and equipment, test results can become unreliable — potentially leading to failed compliance, programme delays, and expensive retesting.

APT Sound Testing removes these risks by providing a complete large-building airtightness testing solution from initial consultation through to final certification.

Supporting Projects from Design to Completion

Modern construction programmes are demanding, and airtightness performance must often be achieved within tight timescales.

APT Sound Testing supports clients throughout the entire process with services including:

• Design-stage consultancy
• Pre-test inspections
• Large-scale air pressure testing
• Diagnostic leakage surveys
• Remedial guidance and support
• Fast-turnaround reporting

Our objective is simple: help projects achieve compliance first time.

Airtightness Testing for BREEAM and Energy Efficiency

For developments targeting BREEAM certification, improved EPC ratings, or enhanced energy performance, airtightness plays a major role in overall building efficiency.

Our testing services support:

• BREEAM Hea 02 and Ene 01 credits
• Improved EPC and SBEM calculations
• Reduced heating and cooling demand
• Lower long-term operational energy costs

On large buildings, even small improvements in airtightness can result in significant energy savings over the building’s lifespan.

Why Choose APT Sound Testing?

APT Sound Testing is trusted nationwide for large-scale airtightness testing because we combine specialist equipment with accredited expertise.

Our services include:

• High-powered blower door systems for buildings above 10,000 m²
• Level 2 ATTMA Registered testing
• UKAS Accredited procedures
• Smoke testing and thermal imaging diagnostics
• Detailed and actionable reporting
• Fast turnaround times
• Nationwide coverage

We continue to support contractors, developers, architects, and consultants across the UK on some of the country’s most demanding airtightness projects.

Contact APT Sound Testing

For large-scale air pressure testing, air leakage diagnostics, or technical advice, contact APT Sound Testing today.

Phone: 07775 623464
Email: info@aptsoundtesting.co.uk
Website: https://aptsoundtesting.co.uk/

Air Tightness Testing – APT Sound Testing

At APT Sound Testing, we provide professional Air Tightness Testing services across the United Kingdom, supporting projects of all sizes, from single residential dwellings to large-scale commercial developments. Our experienced team works closely with developers, contractors, and property owners to ensure buildings meet the required performance standards and achieve compliance with UK Building Regulations.

What sets us apart is that we are UKAS-accredited to carry out both Air and Sound Testing in accordance with Building Regulations and industry standards. Because our engineers are multi-skilled and fully accredited, we can perform Air, Sound, and Ventilation Testing during the same visit. This combined approach saves our clients time and money while improving on-site coordination. Unlike many providers, all of our testing is carried out by our own in-house engineers, we never subcontract our work.

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Why Air Tightness Testing Is Required

Air tightness testing became a legal requirement in 2006 in England and Wales under Building Regulations Part L, which focuses on the conservation of fuel and power. The goal is to create more energy-efficient buildings by reducing uncontrolled air leakage.

Air leakage refers to the uncontrolled movement of air through gaps, cracks, and joints in the building fabric, something most people simply recognise as draughts.

Reducing these air leakage paths helps:

• Improve energy efficiency
• Reduce carbon emissions
• Lower heating and cooling costs
• Improve indoor comfort

When energy escapes through a building’s fabric, it contributes to what is known as the Building Emission Rate (BER). To meet regulatory standards, new developments must achieve specific air leakage targets.

Typical targets include:

• Standard dwellings: around 5.0 m³/hr/m²
• Commercial buildings: often 3.0 m³/hr/m² or lower

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The Impact of Poor Air Tightness

Air infiltration and exfiltration occur simultaneously in buildings. If air enters in one location, it must exit somewhere else.

Poor air tightness can lead to several problems:

1. Increased Energy Loss

Air leaking out of a building must be replaced by conditioned air that needs heating or cooling. This significantly increases energy consumption and operational costs.

2. Condensation and Moisture Issues

In winter, warm indoor air can escape into colder wall cavities where moisture condenses. This can lead to:

• Mould growth
• Rot
• Structural damage
• Poor indoor air quality

3. Indoor Comfort Problems

Draughts can make buildings uncomfortable for occupants. In extreme cases, excessive air leakage can disrupt normal building use.

For example, during one investigation we conducted smoke testing on a building where employees refused to work due to constant draughts. The building had an air leakage rate of 25 m³/hr/m². After identifying and sealing the leakage paths, the building achieved below 5 m³/hr/m², resolving the issue.

4. Pollution Ingress

Excessive air leakage can draw polluted air into buildings from nearby sources such as:

• Busy roads
• Fuel stations
• Waste areas
• Restaurants

Creating a well-sealed air barrier helps control indoor air quality and minimise pollutant entry.

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Our Air Tightness Testing Process

At APT Sound Testing, we use professional blower door testing equipment to measure air leakage accurately.

Step 1: Install the Blower Door System

Our fan system is mounted into a standard door opening (approximately 900mm x 2000mm) and adjusted to fit securely within the frame.

Step 2: Environmental Measurements

Before testing begins, we record environmental data including:

• Internal and external temperatures
• Barometric pressure
• Ambient conditions

Step 3: Pressure Testing

The fan system is activated and pressure readings are taken between 25 Pa and 70 Pa in 5 Pa increments. These readings allow us to measure airflow through the building envelope.

Step 4: Final Calculations

Once measurements are complete, our technicians calculate the air leakage rate at 50 Pascals (m³/h·m² @ 50Pa) based on the airflow required to maintain that pressure difference.

Step 5: Smoke Testing (Leak Detection)

The building is then pressurised to around 50 Pascals, forcing air through any gaps or leakage paths. Using smoke testing equipment, our engineers walk through the property to identify and record the exact locations of air leaks.

This diagnostic stage helps contractors quickly locate and seal problem areas.

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How Long Does Testing Take?

A typical air tightness test and smoke investigation usually takes 2–3 hours per building.

However, we can remain on site for the full day if required. This allows contractors to carry out sealing works immediately, followed by re-testing if necessary.

If you plan to undertake remedial work during the test day, it is helpful to have materials such as:

• Mastic sealant
• Expanding foam
• Draught excluders
• Plasterboard
• Grip fill adhesive
• Safe access equipment

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Air Tightness Consultancy and Design Support

Achieving the required air tightness target is becoming increasingly challenging as regulations continue to tighten. That is why we strongly recommend considering air leakage control during the design stage of a project.

Our consultancy services include:

• Air tightness design reviews
• Construction stage advice
• Pre-completion testing support
• Leakage investigation and reporting

By working with our clients throughout the design and construction process, we can help identify potential issues early and significantly reduce the risk of failing the final test.

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Combined Air and Sound Testing Packages

Most of our clients now choose our combined pre-completion testing packages, which include:

• Air Tightness Testing
• Sound Insulation Testing
• Ventilation Testing

Because our engineers are UKAS accredited in multiple disciplines, we can complete all tests during the same site visit. This eliminates the need to coordinate multiple companies and greatly simplifies site scheduling.

Additional benefits include:

• Reduced testing costs
• Faster project completion
• Improved on-site coordination

We also offer out-of-hours testing, including weekend appointments, to minimise disruption during working hours.

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Nationwide Air Tightness Testing You Can Trust

APT Sound Testing has extensive experience conducting thousands of successful air tightness tests across London and the UK. Our knowledgeable consultants provide friendly, practical advice to help your project meet regulatory requirements quickly and efficiently.

If you’re preparing for an upcoming test, we also provide a helpful air tightness checklist to ensure your building is fully prepared.

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✅ Need help with air tightness testing?
Contact our team today to discuss your project requirements and receive expert guidance from our experienced air tightness consultants. Call 01525 303905 or email: info@aptsoundtesting.co.uk and we will respond as quickly as we can.

Air Tightness Testing Across the UK

At APT Sound Testing, we provide comprehensive air tightness testing services throughout the United Kingdom. Our experienced team works on projects of all sizes — from single residential dwellings to large-scale commercial developments.

We are proud to be one of the few UKAS-accredited companies qualified to carry out both Air and Sound Testing in full compliance with UK Building Regulations and Standards. This accreditation allows us to deliver combined Air, Sound, and Vent Testing packages during a single site visit — saving our clients time, reducing costs, and improving on-site coordination. Importantly, we never subcontract our testing work; all services are delivered by our fully trained in-house engineers.

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Why Air Testing Matters

Since 2006, air testing has been a legal requirement in England and Wales under Part L of the Building Regulations. Its importance continues to grow as the construction industry focuses on reducing carbon emissions and improving energy efficiency.

Part L defines air leakage as the uncontrolled flow of air through gaps and cracks in a building’s structure — commonly known as draughts. When buildings lose energy through their fabric, this contributes to the building emission rate (BER). To meet regulatory approval, new developments must achieve strict air permeability targets:

• Standard dwellings: Typically 5.0 m³/hr/m²
• Commercial buildings: Often around 3.0 m³/hr/m² or lower

Improving airtightness reduces unnecessary heat loss, lowers energy consumption, and contributes to greener, more sustainable buildings.

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The Risks of Poor Air Tightness

Air infiltration and exfiltration can create a range of issues:

• Energy Loss: Escaping air must be replaced and conditioned, increasing heating and cooling demands.
• Condensation & Mould: In winter, warm moist air entering cold cavities can cause condensation, mould growth, and structural damage.
• Uncomfortable Draughts: Uncontrolled airflow can make both residential and commercial properties unpleasant to occupy.
• Indoor Air Quality Concerns: Air leakage can allow polluted external air to enter buildings, particularly in locations near busy roads, fuel stations, restaurants, or waste storage areas.

We have previously tested buildings with air leakage rates as high as 25 m³/hr/m² — far above acceptable levels. After identifying and sealing leakage paths, the same buildings were brought below 5 m³/hr/m², dramatically improving comfort and performance.

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Our Consultancy & Pre-Completion Support

Achieving compliance starts at the design stage. We offer air tightness consultancy and detailed design reviews to help ensure your project meets its targets first time.

Our support includes:

• Early-stage air leakage line design advice
• Pre-completion inspections
• On-site testing for building control sign-off
• Weekend and out-of-hours testing services to minimise disruption

To avoid costly failures, we strongly recommend considering air barrier design as early as possible in your project.

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Combined Air & Sound Testing Packages

Because our multi-skilled engineers are UKAS accredited for both disciplines, we offer significant savings through combined testing packages. Our popular “3-Step Pre-Completion Package” allows clients to avoid employing multiple contractors, simplifying project management and improving efficiency.

By conducting both tests on the same day in a structured and coordinated manner, we help streamline site operations and reduce downtime.

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What Is a Blower Door Test?

Air tightness testing is carried out using blower door equipment, which measures:

• The airflow entering or leaving a building
• The pressure difference across the building envelope

This data helps estimate energy performance under various weather conditions and supports equipment sizing and energy consumption predictions.

Using blower door and smoke testing, we can accurately locate leakage paths. While some issues stem from large, obvious gaps, more often it is multiple smaller leaks that contribute most significantly to poor results. Our experienced engineers quickly identify and document these areas so corrective action can be taken efficiently.

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Protecting Energy Performance and Occupant Health

Excessive air leakage can:

• Increase heating and cooling costs
• Cause condensation, mould, and rot
• Reduce occupant comfort
• Allow outdoor pollutants to enter the building

A well-designed and properly installed air barrier is essential for controlling both air quality and air quantity within a building.

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Work With Experienced Air Tightness Specialists

APT Sound Testing has extensive experience delivering thousands of successful air tightness tests across London and the wider UK. Our in-depth knowledge of Approved Document L ensures your development is supported from concept through to completion.

By working collaboratively with clients throughout the design and construction phases, we help identify practical solutions to minimise air leakage and achieve compliance first time.

If you are preparing for an upcoming test, we recommend reviewing an air tightness checklist to ensure your project is ready.

For friendly, expert advice tailored to your development, contact our team today on 01525 303905 or via our online contact form to discuss your air testing requirements.

Why Is Air Tightness Testing Important?

Maintaining a continuous and well-sealed air tightness barrier is essential for any building’s energy efficiency. Air tightness testing measures how much air escapes from inside the building to the outside through unintended gaps or leaks. When air leaks occur, they not only cause uncomfortable draughts but also significantly reduce energy performance.

A poorly sealed building can lose up to 50% of its heat through air leakage. This undermines the benefits of investing in energy-saving measures such as additional insulation, high-efficiency boilers, or renewable heating systems like ground source heat pumps.

Prioritising air tightness testing ensures your building performs as designed—helping you save money on energy bills and meet regulatory requirements. In fact, failing an air tightness test could prevent you from achieving Building Control sign-off and handing over the property.

By carrying out a test, you’ll receive a measurable air leakage rate (in m³/hr/m²), which indicates the volume of air lost or gained. This figure is then compared to the limits set by Building Regulations, determining whether the property meets compliance standards.

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What Building Regulations Govern Air Tightness Testing?

Air tightness testing is required under two main parts of UK Building Regulations:

• Part L1A – Governs air tightness for all new dwellings.
• Part L2A – Applies to commercial and public buildings such as offices, schools, and retail spaces.

Compliance with these regulations is enforced by Building Control.

Air tightness testing is also a crucial component of both SAP (Standard Assessment Procedure) calculations for domestic buildings and SBEM (Simplified Building Energy Model) assessments for commercial ones. These assessments determine a building’s overall carbon footprint, which is directly influenced by how airtight the structure is.

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What Happens if the Building Fails the Air Tightness Test?

At Air Pressure Testing, our goal is for your building to pass the first time. However, if the initial test doesn’t meet the required standard, we’ll work with you to identify and resolve the issues quickly to ensure a successful retest.

Some of the diagnostic techniques we use include:

• Commercial Smoke Testing: We fill the building with smoke and then pressurise it to highlight leakage points — the smoke visibly escapes through gaps in the envelope. For smaller properties, we use handheld “smoke pencils” to pinpoint problem areas.
• Thermal Imaging: Using infrared cameras, we can identify hot and cold spots throughout the building, helping locate areas of heat loss and air leakage.

Unlike some testing companies that simply test and leave, we provide a proactive support service, assisting you until your building achieves full compliance and Building Control approval.

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Common Causes of Air Leakage

Air leakage can occur in many areas, often due to construction detailing or poor installation. The most common problem areas include:

• Junctions between external walls and floors
• Behind fitted kitchen or bathroom units
• Around poorly sealed windows and doors
• Around service penetrations (pipes, ducts, cables, etc.)
• Through attic or loft access doors

By addressing these weak points early in the construction process, you can dramatically reduce the likelihood of air tightness test failures later on.

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Need Expert Air Tightness Testing?

If you’d like more information about our air tightness testing and consultancy services, please don’t hesitate to contact Air Pressure Testing on 01525 303905, or visit our website to learn how we can help your project achieve full compliance and energy efficiency.

Why Your Building Needs an Air Tightness Test

When it comes to energy efficiency, keeping a building’s air barrier continuous and leak-free is essential. Air tightness testing measures how much air escapes from inside a building to the outside at low pressure. Even small leaks can create cold draughts and dramatically increase energy use.

Why Air Tightness Matters

Up to 50% of a building’s heat can be lost through an unsealed envelope. That means the money you invest in high-performance insulation, premium boilers, or ground-source heat pumps can be wasted if the structure isn’t airtight. A failed air test can also delay handover, adding cost and frustration to any project.

Testing provides a clear air-leakage figure (measured in m³/hr/m²), which is then compared to the limits set by building regulations. This ensures the property meets efficiency standards and gives you a benchmark for improvements.

Building Regulations to Know

Two main UK regulations govern air tightness:

• Part L1A – for new dwellings
• Part L2A – for commercial spaces such as offices and public buildings

Compliance is checked by Building Control and feeds into energy assessments: SAP (domestic) and SBEM (commercial). Both evaluate a building’s carbon footprint, where airtightness plays a major role.

If Your Building Fails the Test

A first-time pass is the goal, but if your property falls short, targeted diagnostics can identify the leaks:

• Commercial Smoke Testing – Pressurising the building while filling it with smoke reveals hidden gaps as smoke escapes. Smaller properties can use handheld “smoke pencils.”
• Thermal Imaging – Infra-red cameras highlight hot and cold spots, showing exactly where air is leaking.

Unlike companies that simply test and walk away, a good testing service will work with you to plan fixes and retest for compliance.

Common Air Leakage Points

Addressing these trouble spots early can prevent failed tests:

• External wall/floor junctions
• Behind fitted kitchen or bathroom units
• Around poorly sealed windows and doors
• Around service penetrations (pipes, cables, vents)
• Through attic hatches or loft doors

Bottom Line

Air tightness testing is more than a regulatory checkbox, it’s key to comfort, lower bills, and a reduced carbon footprint. By planning for airtight construction from the start and working with a proactive testing team, you’ll protect your investment and ensure your building performs as efficiently as possible.

For expert testing or consultancy, visit the Air Pressure Testing website or call 01525 303905.