Award winning retrofit research from Leeds Beckett at the International Retrofit Conference 2025

All home energy models are wrong but some are useful

Paper title: Comparison of modelling techniques and HTC measurements in a UK dwelling pre- and post- retrofit, presented by Dr Sarah Price

LSI expanded some of the research undertaken as part of the DEEP project on energy modelling tools.  PHPP (the Passivhaus Planning Package) was added alongside RdSAP (Reduced data Standard Assessment Procedure), BREDEM (BRE Domestic Energy Model) and dynamic simulation modelling (DSM), and compared to measurements of the heat transfer coefficient (HTC) using the co-heating test. The subject was a semi-detached 3-bed property retrofitted with floor, wall and loft insulation, new windows and doors and draught proofing. With just one property, conclusions are difficult to draw, but the results were interesting enough for us to continue to model the other 13 DEEP houses in PHPP. For more insights into using PHPP as a tool for modelling existing homes.

A retrofit home’s airtightness results may depend on how it’s measured

Paper: A comparison of low- and high-pressure airtightness test methods in existing UK dwellings, presented by Dr Felix Thomas

All new buildings are required to demonstrate a minimum level of airtightness, with the introduction of CIBSE TM23: 2022 there are now two accepted methodologies to measure the air permeability of a building; the Fan Pressurisation method and the newer Low Pressure Pulse method. Drawing on extensive measurements made in the field with both methods the LSI presented the results of 88 side by side fan pressurisation and low pressure pulse tests to explore how well the two methods agree in older dwellings of differing ages, form factors and constructions. It was found that the two methods were largely in agreement, with an average difference of 2% between the two methods across the sample, however individual dwelling results were found to vary between –84% and 67% indicating more investigation into the relationship between the two tests is required to ensure the two methods can be used with confidence.

Measuring the economic benefits of retrofit can be challenging but not impossible.

Paper: Barriers to the effective assessment of economic benefits of retrofit projects, presented by Sharon Bhorkar

Beyond improving energy efficiency, retrofitting domestic buildings offers multiple economic benefits such as reduced energy bills and creating skilled jobs, which are generally not measured. This research improved on the Build Upon2 (BU2) toolkit to explore the financial benefits of five large scale retrofit projects, which were managed by a local authority in North of England from 2022 to 2025. Conducted in two phases, the study revealed a complexity in acquiring data both at the project and stakeholder levels. In phase 1, participants shared a broad range of insights, from adopting a managerial top-down approach to tweaking and simplifying the data collection and evaluation process. Implementing these suggestions in phase 2 resulted in significant improvement in data collection, with response rates increasing from 17% -22% to 90% -95% across the various economic categories. For further details on how to improve the data collection for evaluating the economic benefits of a domestic retrofit project follow here.

More to learn about simulating heat transfer coefficient measurements

Paper: Simulating HTC Measurements for Increased Confidence in Retrofit Performance Predictions, presented by Mark Collett and Winner of IRC’s Best Paper award

As champions of measuring whole-house building fabric performance, the LSI is always interested in validating novel measurement methods. We typically do this through field trials on real homes, but this can be challenging. This paper investigated whether computational energy simulations could complement field trials, allowing us to test how measurements perform in various conditions that are difficult to capture in the real world.

We simulated QUB measurements on a calibrated virtual model of a semi-detached, three-bedroom house from the DEEP project and compared the results to data from the actual field trial. On average, the simulated Heat Transfer Coefficient (HTC) measurements differed from the field trial results by 12%. This discrepancy was even larger after the virtual house had been retrofitted. Further work is needed to determine the root cause of this disagreement. However, we suspect that heat transfer through air leakage and thermal bridges may be a contributing factor, as these are notoriously difficult to simulate accurately and have a proportionally larger impact on the performance of retrofitted properties.

To find out more about the LSI’s research and find out how they can help you with your research ideas, visit their website or get in touch with Professor David Glew, Director of the LSI.