Energy Efficiency and Historic Buildings: Assessing the Thermal and Hygrothermal Performance of Two Refurbished Dwellings
Author(s): Paul Baker, Iain McCaig
This report presents key findings of research carried out by Historic England to assess the thermal performance and hygrothermal behaviour of two dwellings – one in Derbyshire and one in Cumbria – following fabric improvements to increase energy efficiency. Both houses were of traditional construction with solid masonry walls – one brick, the other stone. In each building, a variety of insulation materials and systems were added to the building envelope. In addition, measures to increase airtightness and enhance the thermal performance of windows and doors were carried out. In both buildings, the U-values of elements of the building envelope were measured in situ. These measurements, together with co-heating and air-tightness tests, were carried out both before and after fabric improvements. The moisture content of building fabric in selected locations was then continuously monitored, with Building 1: New Bolsover monitored for seven years. The aim of this part of the study was to compare the long-term performance and behaviour of vapour-closed and vapouropen internal wall insulation systems. Whether the added insultation would result in moisture accumulation in walls, as had been predicted by numerical modelling, was a question of particular interest. Fabric improvements in Building 1: New Bolsover resulted a reduction in thermal transmittance of the building envelope of nearly 40%. In contrast, the reduction following fabric improvements at Building 2: Appleby was about 10%. Moisture accumulation was not observed in walls at Building 1, except in one that was shaded by an adjacent building. This highlights the importance of solar radiation on the thermal performance and hygrothermal behaviour of the building envelope. This report includes a critical review and evaluation of the methodologies adopted in each building, highlighting limitations. Both projects illustrate the challenges in analysing and interpreting data obtained from buildings in use. These include: the wide range of uncontrollable variables; uncertainties about materials and construction; the complex and dynamic interactions between building fabric and internal and external environments; changes in building ownership and occupation. Inevitably, data gathered are site-specific and the extent to which findings can be applied more widely is limited. However, data from long-term monitoring of building elements and assemblies are needed for the validation of numerical models, such as WUFI®. It is recommended that more controllable and repeatable assessment methodologies are devised for future work.
- Report Number:
- 11/2023
- Series:
- Research Report
- Pages:
- 89
- Keywords:
- Modern Energy Efficiency Building and Landscape Conservation Energy Walls Retrofit Thermal Performance Houses External Wall Insulation Moisture Loft Floor Hygrothermal
