This article was written in collaboration with our members, Energy Saving Trust and Build Test Solutions.
Earlier this year, we published a report making the case for measured performance in government policy. Too many UK households live in homes that are expensive to heat, uncomfortable, and damaging to health - even after installing low-carbon heating or energy efficiency retrofits. We have seen this conversation resurface in recent months, particularly as climate change brings hotter summers.
Currently, a building’s energy performance is predicted based on Energy Performance Certificate (EPC) data. However, it is essential the right measures are selected for each property, with a clear understanding of how that building is performing in practice. This has broad implications for policy, as consumers must be confident that low carbon technologies are worth the investment, decreasing demand, minimising consumer energy costs, and ultimately reducing our carbon footprint.
Our measured performance paper makes the case for using technologies and solutions to measure the in-use performance of each building. This insight, if incorporated into the existing policy landscape, will ensure investment is directed positively, and make sure opportunities to reduce emissions and energy bills aren’t lost.
Our call for more accurate building performance measurement is echoed widely across the industry. Energy Saving Trust, in partnership with Build Test Solutions, recently published research reinforcing this vision, outlining the clear policy value of in-use metrics on the path to Net Zero.
Energy Saving Trust & Build Test Solution’s Perspective: Unlocking Real-World Policy Outcomes
Energy Saving Trust’s report, The Value of In-Use Building Performance Metrics on the Route to Net Zero, provides vital evidence for how UK housing policy must evolve. By evaluating the measured Heat Loss Parameter (HLP) across more than 500 lived-in homes, the research established a critical baseline: while modelled EPC data is broadly representative of average performance across large housing stocks, individual property performance can vary substantially. EPC models only matched measured heat loss in 44% of individual buildings.
Rather than treating this as a simple technical flaw, the report highlights how adopting in-situ measurement could unlock transformative policy outcomes across four critical pillars:
- Targeting Public Spending Efficiently: Major UK Government schemes like Warm Homes funding, and formerly the Home Upgrade Grant (HUG) and Energy Company Obligation (ECO) rely or relied on rigid EPC band cut-offs to allocate funding. Because real-world heat loss varies widely within the same band, billions in public subsidies risk being misallocated to homes that perform adequately. Simultaneously, vulnerable residents in genuinely cold, poorly performing homes above arbitrary EPC thresholds miss out on support. In-use metrics offer local authorities a precise diagnostic filter to target the worst-performing physical structures first.
- De-Risking Green Finance & the Warm Homes Plan: Green mortgages and private retrofit loans currently rely on modelled SAP/EPC predictions. This creates risks for lenders funding measures by overstating expected bill savings and can disadvantage homeowners whose properties perform better in practice than predicted. Using measured metrics provides lenders with more reliable, verifiable performance data. It could also support the development of "pay-as-you-save" finance models and help to unlock private capital to support the Warm Homes Plan.
- Quality Assurance & Consumer Protection: Consumer confidence has been damaged by installation failures and poor retrofit outcomes. Current quality assurance frameworks often place disproportionate emphasis on paperwork compliance rather than whether measures deliver the intended outcomes. Introducing pre- and post-retrofit in-use measurement would shift the focus towards real world results, ensuring homes are warmer, safer and more affordable to heat. This would also better incentivise contractors to deliver high-quality installations, which could be a subtle but powerful nudge.
- Accelerating Heat Pump Adoption: Current heat pump sizing relies on modelled heat loss calculations, which does not always reflect real-world building performance. To manage the risk of underperformance and consumer dissatisfaction, installers often apply additional safety margins, resulting in oversized systems. This can lead to higher upfront and running costs, reduced efficiency and shorter equipment lifespan. Simultaneously, the inaccuracy of estimates also introduces a risk of undersizing despite these safety margins. Accurate in-situ measurement would enable right-sized systems from day one that deliver comfortable homes, improved efficiency and equipment longevity. This would help strengthen consumer confidence in heat pumps and accelerate the electrification of home heating.
Concrete steps: Incorporating measurement into a new normal
Moving toward measured performance does not require replacing EPCs overnight. It means supplementing modelled baselines with robust, empirical, in-situ performance data to provide a more complete picture of how homes perform in practice. To deliver warmer homes, lower bills, and meaningful carbon reductions, we urge policymakers to:
- Embed measured performance metrics into public funding programmes: Introduce empirical heat loss and building performance measurement within future waves of Warm Homes and other related funding; this could initially be on a sample basis.
- Integrate in-situ performance testing into retrofit quality standards: Incorporate whole-house thermal performance measurement into quality assurance standards such as PAS 2035 and MCS assessment workflows.
- Enable data-driven green finance: Establish a clear regulatory framework for lenders to use measured building performance data when designing and underwriting financial products.