Get The Plot Ready Before The Air Tightness Tester Arrives

You have trades finishing off, Building Control asking for paperwork and a handover date that is getting closer by the hour.

The last thing you need is an air tightness test failing because of an unsealed pipe opening, an unfinished loft hatch or a door that was not ready when the tester arrived.

Many of the problems that affect air tightness results are small. However, when they are repeated across a plot, they can add up to a failed test, remedial work and another visit before the property can move towards sign-off.

Preparing properly does not mean trying to hide air leakage on testing day. It means making sure the building is genuinely complete, the designed air barrier is continuous and the tester has the access and information needed to carry out the assessment correctly.

AVT UK works with developers and housebuilders across the UK, helping you organise air tightness testing, identify potential problems and keep plots moving towards completion.

Why You Should Prepare For An Air Tightness Test Early

Air tightness should be considered throughout the build, not only when someone books the final test.

By the time plasterboard, flooring, kitchen units and final finishes are in place, some parts of the air barrier may be difficult to reach. A gap that could have been sealed quickly earlier in the programme may then require finished work to be removed.

Early checks help you:

• Find recurring workmanship issues before they affect several plots.
• Give each trade clear responsibility for sealing its own penetrations.
• Reduce last-minute snagging and repeat visits.
• Protect the air permeability target used within the energy calculations.
• Keep certification and handover moving.

Our Part L compliance checklist for housebuilders explains how air tightness fits into the wider compliance process.

Confirm The Air Tightness Target Before Testing Day

Do not wait until the tester arrives to find out what result the plot needs to achieve.

The site team should have access to the design air permeability target from the relevant energy calculations. The target may be more demanding than the minimum limiting value within the applicable version of Approved Document L.

You should also confirm:

• Which version of Approved Document L applies to the project.
• Whether the building is a dwelling, non-domestic property or mixed-use development.
• The test method that will be used.
• What information the tester needs before attending.
• Whether certification is required for Building Control.
• Who will receive the report and certificate.

Current and transitional projects may be working to different technical standards. Check the project documents and speak to your building control body or testing provider rather than relying on information from another development.

You can view the current Approved Document L guidance on GOV.UK.

Confirm Which Air Tightness Test Is Being Used

Not every air tightness assessment uses the same equipment or site setup.

Fan pressurisation testing uses specialist fan equipment to create a pressure difference across the building envelope. Pulse air testing uses short, controlled pressure pulses to measure how the building responds.

The right approach will depend on the property, the stage of the project, the reason for testing and the evidence required.

Speak to the testing team before the visit so you know:

• What equipment will be brought to site.
• Where it will need to be positioned.
• Which openings will need to remain available.
• Whether a suitable electrical supply is required.
• How long access to the plot is likely to be restricted.
• What test result and certification will be provided.

AVT UK can explain the available air tightness testing options and help you choose the approach that suits your project and compliance requirements.

Do Not Book The Final Test While The Building Envelope Is Incomplete

A plot can look almost finished while still having gaps in the air barrier.

Paint, flooring and fitted kitchens do not make a property ready for testing if service penetrations, access panels or structural junctions are still incomplete.

Before booking the final assessment, check that the parts of the building forming the airtight envelope have been installed and sealed as designed.

Follow The Designed Airtightness Line Around The Plot

Your drawings should identify where the main air barrier runs through the walls, floors, roof and junctions.

Walk the route before testing day and check that it remains continuous.

Pay particular attention wherever the airtightness line changes direction or passes behind another building element. These areas can be missed because no single trade sees the whole route.

Useful questions include:

• Where does the wall air barrier connect to the ground floor?
• How is continuity maintained at intermediate floors?
• How does the wall connect to the ceiling or roof?
• What seals the perimeter of windows and external doors?
• How are party wall and external wall junctions treated?
• What happens where pipes, cables and ducts pass through?

If nobody on site can clearly follow the air barrier around the plot, that should be resolved before the final test.

Inspect The Most Common Air Leakage Points

Air does not only escape through large visible holes.

A series of smaller gaps can have a significant effect on the result, especially when the same detail appears throughout the property.

Common areas to inspect include:

• Window and external door perimeters.
• Door thresholds and seals.
• Pipework and cable penetrations.
• Consumer units and meter cupboards on external walls.
• Waste pipes and soil stacks.
• Ventilation ducts passing through the building envelope.
• Loft hatches and eaves details.
• Wall-to-floor and wall-to-ceiling junctions.
• Bath panels and boxing around services.
• Behind kitchen units and utility fittings.
• Service risers and access panels.
• Attached garages and integral store areas.

Read our guide to what causes air leaks in new builds for a closer look at the defects that commonly affect completed plots.

Check Every Window And External Door

Windows and doors need more than a quick visual check.

Open and close each one. Confirm that the locks engage properly, seals meet consistently and frames are securely fitted.

Check:

• Seals around the full perimeter of the frame.
• Gaps beneath external door thresholds.
• Damaged or twisted weather seals.
• Doors that need adjusting before they close properly.
• Openings around fixing points.
• Junctions hidden behind trims and finishing pieces.

A frame may look neat after the architrave is fitted while still allowing air to pass through the installation gap behind it.

Finish And Seal Service Penetrations

Every trade that passes a cable, pipe or duct through the air barrier has the potential to create an air leakage route.

Make it clear that drilling a hole is only half the job. The penetration must also be sealed using a suitable detail that maintains the designed air barrier.

Check areas completed by:

• Electricians.
• Plumbers.
• Heating engineers.
• Ventilation installers.
• Telecommunications contractors.
• Renewable energy installers.
• Kitchen and bathroom teams.

A final cross-trade inspection is valuable because one contractor may not recognise that an opening affects another team’s compliance work.

Do Not Confuse Airtightness With Ventilation

Airtightness controls unwanted air leakage. Ventilation provides deliberate airflow for indoor air quality and moisture control.

You need both.

Do not permanently block trickle vents, extract terminals or other purpose-provided ventilation to improve the result. The tester will prepare relevant openings in line with the approved testing method.

Your role is to make sure the ventilation system is installed as designed and that the tester knows what is present.

Before the visit, confirm:

• Extract fans and ventilation units are installed.
• Ductwork is connected and complete.
• External terminals are fitted.
• Background ventilators are installed where specified.
• Commissioning work has been completed or scheduled.
• The tester has been told about unusual ventilation arrangements.

Passing an air tightness test does not prove that the ventilation system complies with Part F.

AVT UK can also provide ventilation compliance and background ventilation assessments where both requirements need to be considered together.

You can check the current Approved Document F guidance on GOV.UK.

Keep The Plot Clear While The Test Is Taking Place

An air tightness test needs stable conditions.

Trades repeatedly opening doors, moving between plots or continuing work inside the property can interrupt the process and delay the result.

Before the tester arrives:

• Tell the relevant trades when the plot will be unavailable.
• Arrange access to every room and cupboard.
• Make sure keys are available for external doors.
• Remove materials blocking access to windows, hatches and service areas.
• Provide safe access around the property.
• Keep other workers from entering until the tester confirms the assessment is complete.

Site activity, wind and weather can also affect whether suitable test conditions can be achieved. The tester will decide whether the assessment can proceed safely and in line with the required methodology.

Have The Project Information Ready

Missing information can delay the test report even when the plot achieves its target.

Ask your testing provider what is needed in advance. This may include:

• The full site and plot address.
• The required air permeability target.
• Relevant SAP, energy model or design information.
• Dimensioned floor plans, elevations and sections.
• Details of the building envelope.
• Information about attached garages or unheated spaces.
• Details of ventilation systems and permanent openings.
• The contact details for the site manager and report recipient.
• Building control or certification requirements.

Check that the plot number, postal address and report details are consistent across the documents. A small administrative error can create unnecessary back-and-forth at the point of sign-off.

Consider Testing Before The Final Handover Rush

Waiting until every finish is complete can leave very little time to investigate a poor result.

Early-stage assessment can help identify recurring details while affected areas are still accessible. On a multi-plot development, findings from one property may also help you improve workmanship across the remaining units.

Pulse testing can be particularly useful where you want practical information on building airtightness without relying solely on a final compliance visit.

The timing and method still need to suit the project, so discuss the build programme with AVT UK before fixing the test date.

Air Tightness Test Day Checklist For Site Managers

Use this checklist before handing the plot over to the tester.

What Happens If The Plot Fails?

A failed result does not always mean major reconstruction is needed.

It does mean you need to identify where uncontrolled air is passing through the envelope and put the defects right before retesting.

Start by reviewing:

• Any unfinished or recently altered work.
• Repeated construction details.
• Service penetrations.
• Window and door installations.
• Loft, eaves and roof junctions.
• Areas where several trades have worked.

Our guide to common causes of a failed air tightness test explains the practical next steps.

Where the leakage route is difficult to locate, ultrasonic air leak detection can help pinpoint specific weaknesses so remedial work can be focused in the right place.

Frequently Asked Questions About Preparing For An Air Tightness Test

Can an air tightness test take place before the plot is fully decorated?

Possibly. The important point is whether the permanent air barrier and all relevant building envelope details are complete. Decorative finishes may not matter unless they form part of the airtightness strategy. Confirm the required stage with the tester before booking.

Can we temporarily seal gaps before the test?

Only openings permitted by the approved testing methodology should be treated for the assessment. Temporary sealing should not be used to hide unfinished workmanship or block permanent ventilation. Let the tester control the test setup.

Do all windows and doors need to be closed?

External windows and doors will normally need to close properly for the test. Internal doors and other openings will be arranged by the tester according to the building layout and testing method.

Does an air tightness pass mean the plot meets Part L?

Air tightness is an important part of Part L compliance, but the final energy calculations and other project requirements must also be satisfied. The measured result needs to be entered into the relevant as-built assessment.

Does an air tightness pass confirm Part F ventilation compliance?

No. Airtightness and ventilation affect one another, but they are assessed separately. The ventilation system must still be installed, commissioned and evidenced correctly.

How long should the site remain clear?

The time required depends on the size and complexity of the building, the test method and site conditions. Ask the testing team when booking and allow enough time so the assessment is not rushed.

Keep Air Tightness Testing Off The Critical Path

The best air tightness test is the one that does not create a last-minute drama.

When you confirm the target early, follow the air barrier throughout construction and give each trade responsibility for the openings it creates, testing becomes a planned part of the programme rather than another obstacle to handover.

AVT UK provides air tightness testing, Pulse air testing, Part L certification and targeted air leak detection for developers and housebuilders across the UK.

We will help you choose the right testing approach, organise the information needed and understand what to put right if the plot does not achieve its target.

Explore our Part L air tightness certification and compliance service or contact the AVT UK team to arrange testing for your development.

This article provides general guidance. The testing requirements and technical standards that apply will depend on the building, project type and relevant transitional arrangements. Confirm the project-specific position with your testing provider and building control body.

google flolw