The thermal performance solid wall homes in England

Work on defining the first standard coefficients for thermal transmittance began with experimental work in the 1920s and 1930s, with standardised coefficients published by the Institute of Heating and Ventilating Engineers (IHVE) in 1940 in the IHVE Guide to Current Practice. For a plastered 9” thick (220mm) solid wall, the U-value published in the 1940 Guide was equivalent to 2.44 W/m2K. This value was not revised until the 1970 version of the IHVE Guide. Rather than rely solely on experimental values from full thickness walls, a theoretical calculation was used for this revision. The U-value published in the 1970 Guide was equivalent to 2.10 W/m2K.

In the 2010s my work measured the U-values of over 300 solid walls in-situ. Fieldwork was accompanied by a wide-ranging set of other measurements including:
• Hot-box tests
• Moisture tests
• Thermal conductivity measurements of bricks and mortar
• Comparison of revised theoretical and measured U-values
• Consideration of the implications of findings for theoretical U-value calculations of a typical wall

These results supported U-values which were significantly lower than in use at that time (originally proposed in the 1970 IHVE Guide). This could be attributed to a lower moisture content, and the presence of air gaps within the wall.

Based on these results, the standard U-value coefficient to be used for Energy Performance Certificates (EPCs) for 9” (220mm) thick solid wall was changed to 1.7W/m2K. This represents the most significant revision to solid wall U-value assumptions since 1970. The body of work I present here represents a substantial original contribution to knowledge. The findings have had direct impact on Government policies and current practices and changed the way millions of homes energy ratings are assessed. The research has been cited in government consultations, academic literature, and industry guidance, and has significantly influenced the direction of retrofit policy.

My research also highlighted the variability in the U-value of solid walls due to differences in construction, materials and moisture contents. As energy ratings become increasingly used for regulatory and other policies it is important that new and developing in-situ techniques for measuring U-values are incorporated.

A programme of research, similar to that conducted for solid walls, is also needed for other core building elements, including other wall types, roofs and floors. Many of the assumed standard coefficients for these elements are unlikely to have been challenged in many decades.

There is also a major opportunity to apply machine learning and AI techniques to enhance the assessment and recommendation of retrofit solutions, complementing data from surveys and measurements. The benefits of these techniques, however, are unlikely to be achieved unless the models can be trained on new reliable base data across a range of building elements.