Build Test Solutions says accurate data can benefit retrofit programmes for hard-to-heat homes
To reduce greenhouse emissions, the UK needs to retrofit 26 million homes by 2050. One tool used to drive activity is Energy Performance Certificates (EPCs). The national Fuel Poverty Strategy and the Minimum Energy Efficiency Standards policy both include goals to raise housing up to an EPC rating of C. Research shows that only 40% of homes in England achieve this rating. At a time of spiralling energy prices and a cost-of-living crisis, it shows the scale of the challenge facing landlords and occupiers.
EPC ratings were implemented in 2008 as a low-cost, non-invasive means of surveying a building. They are used as a referencing tool that allows potential homeowners or renters to understand the theoretical thermal performance of a building. They are based on the Standard Assessment Procedure (SAP). The full SAP is used for new build compliance sign-off and can incorporate a range of detailed inputs, such as designed U-values, thermal bridging calculations and air tightness targets. There is also a reduced version (RdSAP), which is used for existing buildings to prepare EPC ratings at the point of sale or letting.
While the existence of EPCs and the underlying methodology are positive, calculations are based on theoretical assumptions of how effective the building is, rather than accurate measurements of the ‘as-built’ real-world product. No two buildings are the same, so the risk of these assumptions being incorrect is very high. Housing regulations appear to be shifting towards greater physical proof of workmanship and thermal efficiency, especially in the retrofit industry. A lower-rated home is likely to suffer from high levels of air leakage, poor thermally performing floors, walls, glazing and roof, and poor ventilation. Good thermal performance is critical to reducing the cost of living and helping maintain good living conditions.
The need for accurate testing
Changing demands by policymakers and homeowners need EPC assessments to go further. Assessments should reflect the uniqueness of each building and help advise the user on the most cost-effective and practical steps they can take to lower running costs, improve comfort levels and reduce CO2 emissions.
Inaccurate EPC ratings can lead to people investing in retrofit solutions that don’t provide the most effective improvements – or worse, lead to unintended consequences. For example, households can spend thousands of pounds increasing the amount of insulation in their homes when the true measured thermal performance of the property might suggest insulation would deliver only marginal gains. Effective measurement could prove that better returns are available by switching to a heat pump and offsetting added electricity load with solar PV.
Testing before and after retrofitting a property provides insight into what action to take and becomes the basis for quality assessment of the installation, materials and retrofit strategies. This data can then also be used to assess the effectiveness of the investments and promote the performance of the building.
Measuring the total rate of heat loss through the building fabric is one of the most important underlying metrics that the industry must focus on. Thermal performance measurement, expressed as a heat transfer coefficient, won’t tell you the exact source of the heat loss, but it can replace a huge number of assumptions and estimates.
Government initiatives such as the Smart Meter Enabled Thermal Efficiency Ratings (SMETER) Innovation Programme have demonstrated how to measure total building heat loss using widely accessible data such as energy consumption and internal temperature.
Thermal performance measurement systems, such as SmartHTC, work by taking internal temperature and energy consumption measurements while the property is occupied and lived in as normal. These systems use smart meters to measure gas and electricity consumption in 30-minute intervals over a three-week period, or by taking meter readings before and after testing. Internal temperature is monitored during winter (October to March in the UK) to assess how heat escapes from the building. The measurements and some basic information about the building, such as the floor area and location, are then fed into a cloud-hosted algorithm via a browser interface or APIs. The thermal performance is instantly returned.
Assessing air leakage and U-values
Once heat loss is measured, assessors need to investigate the primary reasons by looking at airtightness and the thermal performance of individual building elements such as walls, floors and the roof.
Air leakage typically accounts for a third of total space heating demand. Tests, such as the traditional blower door fan method, use a doorway-mounted fan to both pressurise and depressurise a building at high pressures. There are also new technologies, such as Build Test Solutions’ Pulse, which uses compressed air to provide a measurement of the air leakage rate at normal pressure levels. Rapid non-invasive methods of measuring the rate of heat loss through building elements such as Build Test Solutions’ Heat3D and heat flux plates remove the need to calculate the U-value of a structure by measuring the as-built performance of a given building element, before adding insulation or carrying out retrofit works.
Smart Meter Enabled Thermal Efficiency Ratings (SMETER) Innovation Programme: bit.ly/gov_smeter
Measurement of whole building fabric heat loss (also known as a Heat Transfer Coefficient or HTC): bit.ly/BTS_HTC
Air leakage measurement: bit.ly/BTS_pulseair
What is key here is that for hard-to-heat homes, there’s no quick fix or one-size-fits-all solution. More investment in measuring and understanding performance can pay dividends down the line. If retrofit strategies are informed by more accurate data, the industry will undoubtedly start seeing a shift in the quality and in-use performance of buildings, with regulations catching up and more consistently demanding actual data rather than guestimates. It is the only effective way to improve the performance of our homes and reach our net-zero goals.
For more on measurement, visit buildtestsolutions.com