Air Permeability Testing

Passing the test for air tightness

In accordance with building regulations, it is mandatory to produce measurements for air tightness for newly built homes. Tests to establish such figures go by various names:

  • Air leakage testing
  • Air testing
  • Air pressure testing
  • Airtightness testing
Air Tightness Testing

On completion of a build, a key component of our business is testing for airtightness. Testing for air permeability is critical for any build. Results affect a building’s energy performance.

Air Permeability Testing – The Facts

Various factors affect air leakage, but as a rule of thumb, the target figure for new builds is 5m3/hm2 or under (air leakage rate/hour, for each square metre).

This ‘pass or fail’ result is generated by a specialist engineer and indicates how much air is being sucked into a building — known as ‘leakage’— when the fan used to make such calculations functions at 50 Pascals.

Tests of this sort measure uncontrolled air leakage. They do not take account of trickle vents, extractor fans, or ventilation technology. Pre-designed ventilation inlets and outlets are sealed in advance of the testing. In this sense, air permeability testing identifies fissures in the building’s fabric.


There are certification methods that set out to exceed building regulation standards – Passivhaus, for exam-ple, permits new builds an upper limit of only 0.6 changes of air per hour. When making comparisons, please note existing variations in metrics and procedures used during testing.

The timing of air testing, though not proscribed, usually takes place near the end of a project, before final SAP Calculations and an EPC are released.

For residential builds, test results are passed to a SAP assessor who then updates all calculations, validates a pass and issues final reports, and an EPC.

Effects in SAP

SAP ratings can be significantly impacted by air leakage rates, as serious levels of uncontrolled air leakage reduce a building’s energy performance. SAP Assessors tend to set air permeability targets between 5-10m3/hm2. This is a reasonable expectation, but sometimes this target needs to be lowered for houses hav-ing difficulty meeting their emissions targets. The construction of extremely airtight dwellings sounds like a great idea, but not all dwellings are designed for extremely low levels of ventilation.

Ventilation engineers sometimes assert a ‘maximum’ airtightness of 4-5m3/hm2 as a healthy rate for a natu-rally ventilated house i.e., ventilated only by extractor fans, trickle vents, and windows. Tighter than that would necessitate forced ventilation of some sort.

Some mechanical vent systems feature a heat recovery function (MVHR) whereby heat is extracted from wet rooms and recycled elsewhere in the house.

Tips from a test engineer

Here are 12 top tips for the best results, from one of our senior engineers, Marc.

1. Decide from the get-go how you are going to deal with airtightness
“Set early targets. And make sure all stakeholder tradesmen take part in a pre-start toolbox talk. Everyone involved needs to be aware that the plan is to create an airtight building.”

“Ensure that all necessary SAP calculations have been made and that all results have been accurately rec-orded for every property tested. You can find this number on the SAP report (under, q50, DAP, or Air Per-meability).”

You may find it helpful to mark out an airtight barrier early on. Draw a line connecting all areas which sepa-rate heated elements from unheated elements. As an additional control measure, why not appoint a single focal point on all airtightness issues for concerned parties”.

2. Carry out regular inspections throughout the building program
“To counter the effects of shoddy workmanship, consider installing an inspection schedule during construc-tion. You will want to avoid test failures at all costs since these lead inevitably to costly remedial work.”

One common source of leakage happens when cavity walls are breached at the time of construction – commonly in the vicinity of floor joists. Be sure to use industry-standard fixings to prevent this”.

3. Take care with dry lining
“Plasterboard put in place with the dot-and-dab method can prove problematic. Undetected leakage in brick or block may leave an unwanted path from board to floor slab. Two solutions spring to mind. The first is to initially parge-coat the wall. The other is to lay continuous lines of adhesive round board sides, and socket cut-outs.”

4. Seal all pipework
“Be sure to seal all waste and supply pipework at the exact places where it passes through floors or walls. Use approved, gunned sealants (for bigger gaps use pre-compressed strips of foam, which are flexible and expandable. Avoid foam — it shrinks too readily, breaking the seal. There are flexible foams on the market, specifically tested for use in airtight projects”.

5. Doors and windows
“As an expert in the field, I see plenty of door and window frames that have been incorrectly sealed. Save yourself a lot of heartaches —always use suitable seals and sealants to avoid gaps wherever they are locat-ed.”

6. Radiator pipework
“Underfloor manifolds or radiator pipes aren’t always sealed when the floor is screeded. This problem is of-ten compounded by covered gaps with flooring. Also, radiator pipes often pierce walls behind a radiator. This is a very difficult area to access and check.”

7. Make sure you include eaves, loft hatches, and cupboards
“In homes which include roof space rooms, it is common to find air leaks at the eaves, around cupboard doors, and in loft hatches. Such rooms are often added later, effectively partitioning unheated space from living space proper, so it’s best to seal these as efficiently as any external door or window”.

8. Pay particular attention with light fittings
“Take care to properly fit all light switches and fittings, electrical appliances and plug sockets before being tested, since temporary sealing of these components is prohibited. Improper fitting runs the risk of air loss leading to poor results.”

9. Seals around services
“All modern homes are serviced. So be aware that pipework for water, drainage, and gas; flues servicing boilers, and areas housing electric cables commonly leak – we regularly come across leakages in meter boxes”.

10. Bathrooms
Bathrooms offer the perfect opportunity for air leakage. The main culprits are bath panels and pipework. Ensure that all avenues for air leakage are adequately sealed before attaching bath panels, covers for vani-ty units, extractors, and anywhere that requires boxing-in.

11. Skirting boards must be sealed
For optimum efficiency, seal all skirting boards top and bottom, with silicone sealant. You should not rely on traditional carpets or other floorings to stop air leakage.

For best effect, ensure that kitchens are finished. This includes all appliances, any required boxing-in, and the full installation of extractors. It is no surprise that in common with bathrooms, leakage in kitchens is often detected where there is pipework. Don’t forget the cavities behind kitchen cupboards!

The Regulations

Building Regulations have tightened during the last ten years — a period that has seen design air permeabil-ity (DAP) figures go up.

In short, it isn’t easy to determine when a building is in a state of perfect readiness to meet SAP perfor-mance figures.

The Risk of Testing Early

ATTMA (Air Tightness Testing and Measurement Association), recently revealed a seventy percent failure rate in dwelling tests as a direct consequence of calling in testing companies too early. Early testing could end up costing you dearly: there’s the cost of re-testing for a start, not to mention unforeseen person-hours and possible penalty payments for delayed handovers.

You’ll most likely come under pressure to bring the project in on time. And with sub-contractor delays be-yond your control, you may be tempted to ‘just get air leakage testing done and out of the way.’ Don’t be tempted; be professional. And let the seventy percent failure rate statistic in the previous paragraph sound a cautionary note.

So when is the best time to arrange an Air Leakage Test?

Our recommendation is to conduct air leak testing after the completion of all building work (including snag-ging) —when all doors and windows have been fully fitted and the property connected to power and water supplies. For perfect testing conditions, test before laying flooring or the installation of furnishings.

Avoid the Mastic Trap

Official guidelines make clear in which circumstances temporary sealing is permissible. The key contractor is held responsible for any temporary seals in line with ATTMA guidelines. A straightforward method for temporary sealing is to employ low-tack masking tape.

Permissible temporary seal areas:

  • Extractor fans in bathrooms and kitchens (and other mechanical ventilation systems.)
  • Trickle vents
  • Grilles used for AC purposes
  • Passive ventilation: air bricks, passive stacks or sub-floor ventilation systems
  • Chimney flues

How We Can Help

Briary Energy happily offer general air leakage design advice and onsite guidance.
Post project completion, we provide Nationwide IATS accredited air leakage testing to assist you in demonstrating compliance with building regulations.

Why Choose Us?

  • Discounts for SAP/SBEM Calculations
  • Full UK Coverage
  • Experienced and Accredited Team
  • Practical Advice
  • Same Day Certificates

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Contact us today to talk about your upcoming project – it could save you on average £800* per plot!

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