Performance Evaluation of a Historic Building

Shortlisted: Learning from Projects

Garth House, Oxfordshire, the subject of study
Garth House, Oxfordshire, the subject of study

Historic buildings usually come with high fuel use and low comfort levels for building users.  Attempts to improve their energy efficiency through refurbishment can pose a number of challenges, including the need to preserve the historic character and building features. To tackle these and select appropriate refurbishment measures, it is important that reliable information is available concerning their physical characteristics (construction, energy, environmental performance) and the actual experience of occupants.

This research project, Low-energy, In-situ Refurbishment and Building Performance Evaluation of a Historic Town Council Building, deployed and evaluated an innovative low energy refurbishment of a historic town council building (Garth House) in Bicester, Oxfordshire, underpinned by a systematic building performance evaluation approach pre- and post-refurbishment. Pre-refurbishment monitoring established the baseline performance and revealed issues of ‘chilliness’ from low surface temperature walls and low response times to heating the spaces, despite heating being on 24 hours a day.

Funded by Innovate UK, the refurbishment addressed the challenges of maintaining the historic character and minimising disruption for building users while improving comfort, by deploying an innovative internal insulation technology on the internal face of external walls, integrated with secondary glazing and ventilation systems. The central strategy was to create a new airtight and continuous thermal envelope that was integrated with the existing structure. The key innovation was WHISCERS (Whole House In-Situ Carbon and Energy Reduction System), a technique to rapidly apply internal wall insulation while the building remains occupied – its first use in the UK on a non-domestic historic building.

There were seven key findings from the study. First, the refurbishment solution created a new thermal envelope that was integrated with the existing structure by deploying an innovative internal insulation technology on the internal face of external walls, integrated with secondary glazing and ventilation systems. Secondly, air permeability of the building fabric was reduced from 20.5m3/h.m2 @50Pa to 10.6 m3/h.m2 @50Pa post-refurbishment – doubling its air-tightness. After the refurbishment, gas consumption fell by 67% and electricity by 22%. Overall energy consumption was reduced by 58% and carbon emissions by 48%. These savings match the designed performance of Garth House hence eliminating a performance gap. Over a three month period, moisture content in the external walls and the timber joists stayed under 20%, below which rot does not develop.

After the refurbishment temperatures in most of the rooms ranged between 15-23°C during winter and 20-26°C during summer. There was no overheating and CO2 concentrations remained below 800ppm for over 70% of occupied hours. The questionnaire survey results revealed a positive opinion from occupants, who found the spaces comfortable in both summer and winter. The project demonstrates that it is possible to make significant energy-savings in a historic building in continuous occupation. 

 

Secondary glazing and skylights at Garth-House
Secondary glazing and skylights at Garth-House

The innovative refurbishment of Garth House demonstrates the wide-ranging benefits of energy efficiency for businesses, including significant energy bill savings, reduced carbon emissions and increased wellbeing for occupants. The project successfully demonstrated that refurbishments do not have to affect the use or appearance of heritage buildings. Pre and post-refurbishment evaluation using the BPE approach has demonstrated the possibility to eliminate the performance gap which most buildings are prone to. With 12 months of detailed monitoring on the actual energy and environmental performance of the retrofit, the project offers significant information and the opportunity for shared learning to help other organisations implement their own projects. The lessons learned from this project have been extended to other planned refurbishment projects in Bicester such as the Eco Bicester Living Lab initiative.

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Research by Prof Rajat Gupta and Dr Adorkor Bruce-Konuah, Oxford Brookes University, UK; Adrian Kite, Ridge & Partners LLP, UK; Alex Towler & Nicole Lazarus, Bioregional, UK; and Susan Mackrell, Bicester Town Council, UK

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