New home airtightness testing measures the hidden air leaks that listing photographs and polished finishes cannot reveal. A few weeks before completion, someone closes every window, temporarily seals ventilation openings according to the test procedure, and depressurises the house to 50 pascals with a fan mounted in the front door. The result is a single number on a certificate. Once that number clears the compliance requirements, buyers may hear little more about it.
The number is air permeability, measured in cubic metres of air leaking through the building envelope per square metre of surface area, per hour, at that 50 Pa pressure difference. It measures gaps around service penetrations, behind skirting boards and where a window reveal meets a wall. A home can look immaculate and still have significant air leakage. Testing under pressure helps reveal what appearance alone cannot.
What New Home Airtightness Testing Measures
A blower door test creates a controlled pressure difference between the inside and outside of a home. The equipment measures the airflow needed to maintain that difference, allowing the tester to calculate how much air escapes through the building envelope.
The result describes the airtightness of the property under test conditions. It does not, by itself, confirm the quality of insulation, demonstrate that ventilation works correctly or explain how comfortable every room will feel.
That distinction matters. A certificate provides useful evidence, but its value comes from understanding the measured result alongside the home’s design, ventilation system and construction details.
What the Regulations Actually Require
Building regulations set minimum standards, while an individual property’s design may require a tighter result to achieve its energy performance calculations. Buyers should therefore ask which regulatory requirements and design targets applied to their home.
A regulatory maximum is a ceiling rather than a measure of exceptional performance. A home that clears that limit may still perform differently from one designed and built to a more demanding airtightness target.
Research using 192,731 pressure tests lodged with ATTMA between August 2015 and December 2016 found that measured air permeability clustered around design targets. Mean results ranged from approximately 4.2 m³/h·m² for homes with mechanical ventilation and heat recovery to 4.7 for naturally ventilated homes.
The dataset also indicated that 92 percent of sites had only one test lodged. That does not establish whether additional testing or remedial work took place outside the records, but it raises a useful question for buyers: what was checked, and at what stage?
Passivhaus uses a different measure of airtightness: air changes per hour at a specified pressure difference. Because this is based on building volume rather than envelope area, the figures should not be compared directly without the relevant building dimensions.
Why New Home Airtightness Testing Matters
Uncontrolled air leakage can allow heated air to escape and outside air to enter through unintended gaps. This may contribute to draughts, uneven temperatures and additional heating demand.
However, airtightness needs to work alongside an appropriate ventilation strategy. Reducing accidental air leakage does not remove the need to supply fresh air and extract moisture from kitchens, bathrooms and other occupied spaces.
A tightly sealed home with inadequate ventilation can experience poor indoor air quality and moisture problems. The aim is a well-sealed building with ventilation that is properly designed, installed and commissioned.
Insulation also forms part of the picture. A wall can have a good calculated U-value while gaps in insulation or poorly detailed junctions reduce its actual performance. Air leakage and thermal bridging are different defects, although they can occur in the same areas.
During new home airtightness testing, leak-detection checks may help identify draughts around junctions and penetrations. Other investigations may be needed to assess insulation continuity or thermal bridges.
What to Ask About New Home Airtightness Testing
Start by requesting the final as-built airtightness test report. Ask for both the measured air permeability and the design target, rather than relying only on a headline energy rating.
Check that the report identifies the correct property and records when the test took place. The timing matters because later work can disturb the airtightness layer.
Electricians, plumbers and kitchen installers may need to make additional penetrations. If work continued after the test, ask how those openings were sealed and whether any further checks were undertaken.
Useful questions include:
- What air permeability result did the home achieve?
- What was its design airtightness target?
- Was the test completed before or after the final service installations?
- Were any leaks identified and repaired?
- Was the property retested following remedial work?
- Has the ventilation system been commissioned, and are operating instructions available?
An EPC is useful, but it is not a substitute for the underlying test report. Ask which measured airtightness result was used in the final energy assessment and whether it matches the certificate supplied.
Looking Beyond the Property Photographs
None of this is easy to judge from a listing photograph. When considering a property from a developer such as Folia Homes, ask for the as-built airtightness result and supporting ventilation information before sign-off.
New home airtightness testing is most useful when treated as evidence of construction quality rather than simply another completed document. Understanding the result, the test timing and any subsequent work gives buyers a clearer picture of what they are purchasing.
It is easier to ask these questions before completion than to investigate unexplained draughts or discomfort after moving in. Attractive finishes matter, but the less visible details also deserve a place on a buyer’s checklist.
For more on what shapes a property’s long-term performance, explore energy efficiency in new-build homes.
