With RdSAP 10 launching on 15th June, Domestic Energy Assessors (DEAs) will soon have the opportunity to include air pressure testing results in their assessments. This is a significant step towards improving the accuracy of EPCs. To make the most of this update, it’s essential that assessors understand what air tightness testing involves, when it can be included in an EPC assessment, and the advantages it brings to both assessors and homeowners.
What Is Air Pressure Testing?
Air pressure testing, also known as air tightness testing, measures how much air escapes from a building unintentionally. These leakages can occur through small cracks, poorly fitted windows, or gaps around doors and skirting boards. The test produces an air permeability score, which indicates the rate at which air escapes — the higher the score, the more leakage is occurring.
High air leakage rates can increase energy bills and carbon emissions, as more heat escapes from the building and more energy is needed to maintain comfortable indoor temperatures. Because of this, air tightness plays a key role in a building’s energy efficiency.
Why Are Air Pressure Tests Necessary?
Air tightness testing has been requirement for new builds in England, Wales, Scotland and Northern Ireland. It forms part of compliance with the Building Regulations — specifically:
- Approved Document L in England and Wales
- Section 6 of the Building Standards in Scotland
- Technical Booklet F1 & F2 in Northern Ireland
These tests confirm that the building meets the design-stage air permeability target, as determined in SAP calculations. Maintaining a good level of air tightness is essential for effective insulation and heating systems. Without it, up to 40% of a property’s heat could be lost. Even when homeowners invest in energy-saving upgrades like new boilers or insulation, poor airtightness can render these measures far less effective. Additionally, it can lead to a whole host of other issues including risk of damp and mould or simply reduced comfort for the occupier. This makes air tightness a particularly important figure when it comes to retrofit projects.
What are the relevant standards for air tightness testing?
Air pressure testing in the UK follows the TM23 guidance developed by CIBSE (the Chartered Institution of Building Services Engineers). TM23 outlines standards for testing both domestic and commercial buildings and recognises two approved methods: the ‘Blower Door’ test and the more recent ‘Pulse’ test.
Two Types of Air Pressure Testing
As mentioned previously, there are two recognised methods for air pressure testing, ‘Pulse’ and ‘Blower Door’. Here’s a closer look at how they both work.
Pulse
The Pulse test, introduced in 2022, is the newer of the two methods. It involves placing a pressurised device on the ground floor of the property. This device releases a controlled amount of air and measures the building’s response by tracking changes in internal pressure. It’s a non-intrusive test, and occupants can remain in the home during the process — as long as internal doors stay open and external windows remain closed.
Blower Door
The Blower Door test is a more established method. A large fan is mounted in an external doorway to either pressurise or depressurise the building. Sensors then measure how much air is needed to maintain a set pressure of 50 Pascals, which gives a clear indication of the building’s airtightness. The result is expressed in cubic metres of air lost per square metre of building envelope, per hour (m³/m²/hr @50Pa). As with the Pulse method, the test can be performed while the property is occupied, as long as al internal doors remain open and external windows stay shut.
RdSAP 10 Introduces the Option to Enter Air Tightness Results
In the current version of RdSAP, it uses standard air permeability values based on the age and type of the building, which might not reflect how airtight the property really is. For example, an older home that’s been well sealed could be unfairly marked down because of this default value.
RdSAP 10 introduces a valuable new feature: the ability for DEAs to input verified air pressure test results into their assessments. This option allows assessors to override the default air permeability assumptions where test results and supporting evidence are available. With more homes now undergoing air pressure testing, this update will provide assessors with the tools to generate more precise and accurate EPCs.
New Convention!
A new convention has been added to the latest RdSAP 10 (v12) Conventions document that states the following:
Convention 10.01
The pressure test result must be RdSAP default values and must not be overwritten unless specific documentary evidence is available.
This is the measured air permeability figure (m3/m2/hr) from either a blower door (50Pa) test or a low-pressure pulse (4Pa) test. Documentary evidence will be via a pressure test certificate that has been produced by a person with suitable expertise and experience.
Evidence of suitable expertise and experience can be demonstrated by membership of a recognised air tightness Competent Persons Scheme (EAS or ATTMA), that is approved by Government.
Results from background ventilation tests are not included in the assessment.
What Difference Will Air Pressure Test Results Make In Terms Of EPC Points?
The number of extra EPC points a property can gain from an airtightness test depends on a few key things:
- The property’s starting point: If no energy upgrades have been done and the test is just being used to replace the standard value, the number of points gained (or lost) will depend on how the test result compares to the default. The lower the air permeability, the better. Many homes test between 6–10, while the default is usually 15 m³/m²·h@50Pa.
- The level of airtightness achieved: If energy improvements have been made—like insulation or sealing gaps—that also lower air leakage, the gains from an airtightness test can be even greater. Retrofit work often brings results between 3–6, or even lower, meaning bigger EPC improvements.
- The property’s overall efficiency: The effect of airtightness on the EPC score also depends on other factors like insulation, heating systems, and any renewable energy features the home has.
Although the exact number can vary, a good airtightness result—either through testing or making improvements—could boost the EPC score by 1–3 points. In some cases, that might even push the property into a higher EPC band. Since the bands are based on score ranges, even a small change can make a noticeable difference.
The Impact of Air Pressure Testing on EPCs
By allowing verified air tightness testing results to be included, RdSAP 10 allows for a more accurate assessment of a home’s energy performance. This means EPCs can better reflect a property’s real-world condition and help homeowners make informed decisions about further improvements. Ultimately, this change could lead to higher EPC ratings and more effective implementation of energy-saving measures.
