Salford expert calls for changes to national energy assessments for buildings

The paper, authored by Dr. Richard Jack and Luke Smith of Build Test Solutions, Professor Richard Fitton of the University of Salford, and Andrew Parkin and Chris Ricketts of Elmhurst Energy, proposes the formal inclusion of in-situ U-value measurements as an allowable input to energy models such as RdSAP, HEM, SAP, and BS EN12831. U-values measure the rate of heat transfer through a building element (like a wall or roof), and their accuracy is a key determinant of an energy model's outputs.

These models produce EPCs and size heat pumps. Inaccuracy in their outputs directly undermines all policy measures aiming to reduce building emissions, alleviate fuel poverty, and provide quality assurance on new builds and retrofits. Collectively, this seemingly simple update could increase efficiency and derisk billions of pounds of annual retrofit funding across policies such as the Warm Homes Plan, the Boiler Upgrade Scheme and Minimum Energy Efficiency Standards (MEES).

Beyond these policy measures, the change would have a direct and meaningful impact on all residents and landlords. By accurately representing a home's performance using in-situ measurement, owners could evidence their home significantly outperforms typical assumptions and achieve a higher EPC rating, which can make a massive difference when selling and particularly renting a property. Alternatively, a measurement can provide clear evidence of underperformance to assist with dispute resolution and guide remedial measures and effective retrofitting.

The Problem with Assumptions

Current practice heavily relies on U-value lookup tables based on a visual assessment of construction type and age. However, analysis of past field trials reveals that these assumptions carry significant uncertainty. The uncertainty in estimating a U-value for a known construction type is shown to be at least 45% at best, and for some constructions, it exceeds 100%.

This variability can materially affect EPC ratings. Modelling shows that the observed uncertainties in wall U-value estimation can shift SAP ratings by 5–10 points, a difference large enough to cause a shift from one EPC band to another in nearly all cases studied. For a non-domestic building example, the impact is even more profound, with a single wall type's U-value uncertainty causing an enormous range in EPC band, from C to F, and affecting predicted annual CO2 emissions by 77%.

A Scalable Solution for Accuracy

Measured U-values offer a scalable, accurate, and robust solution to this pervasive problem. The paper argues that integrating measured U-values would be a simple change to implement, requiring only minor alterations to the RdSAP conventions, since U-values are already a manually adjustable input to energy models.

“Measurements carried out by numerous leading practitioners across over 450 different walls clearly demonstrate that it’s practically impossible to reliably predict U-values,” says Dr. Richard Jack. “Quick, simple, non-invasive in-situ U-value measurement techniques exist today that allow building elements to be understood much more accurately, ensuring that retrofit efforts are effective, and that energy assessments are accurate and trustworthy."

Multiple Benefits Across Policy and Practice

The formal inclusion of measured U-values would unlock significant long-term benefits:

• Better Targeting of Retrofit Spending: Accurate data can prevent the inefficient prioritisation of buildings performing better than assumed and highlight those that perform worse due to hidden issues, ensuring funding is directed where it will have the greatest impact, especially for fuel-poor households.
• Enhanced Quality Assurance: In-situ measurement provides an objective, evidence-based benchmark for evaluating the success of retrofit works, moving beyond limited paper-based assessments. For new builds, targeted U-value testing can cost-effectively identify construction practices that lead to performance gaps, enabling immediate design and process refinement.
• Refining Energy Models: Systematically lodging measured U-values alongside assumed ones would rapidly generate an evidence base to refine and improve the national lookup tables over time.

The Path Forward

The paper calls for the energy modelling community, government, and accrediting bodies to formally recognise and embrace in-situ measured U-values. The proposed short-term actions include:

1. Updating domestic RdSAP conventions to allow U-value measurements in line with ISO 9869, requiring reasonable assurance of measurement quality.
2. Establishing competent persons schemes or expanding existing ones for in-situ U-value measurement to assure quality.

“Elmhurst are currently forging ahead to establish a structured, robust governance framework to protect consumers and uphold confidence in energy performance data”, says Elmhurst’s Head of Consultancy, Chris Ricketts. “This is essential because everyone who relies on EPCs and energy models, from homeowners and landlords to retrofit professionals, funding bodies and policymakers, needs confidence that the figures are accurate. When measurements are carried out by trained and competent professionals using agreed methods, the results are consistent, robust and trustworthy. Establishing a recognised professional scheme is the most effective way to ensure that measured U-values can be confidently used across the industry to drive better retrofit decisions and more reliable energy assessments.”

This change is deemed necessary to deliver a "step-change in the accuracy, reliability, and policy value of energy assessments" across the UK.

Resources:

• Download the full report: Click here
• View the open letter to DESNZ and MHCLG: Click here