Upper Floor, 16 Lower Borough Walls, City Centre
16 Lower Borough Walls forms part of a Grade II Georgian terrace; whilst originally residential, the upper floors of the building have now been converted into office space. It is situated within the core of the Bath conservation area and World Heritage site, and positively contributes to its contextual streetscape of largely Grade II terraces that now serve as shops.
BPT strongly supports the principle of sensitive energy-efficient retrofits within historic buildings to ensure their consistent and sustainable usage, whilst helping to reduce energy consumption and carbon emissions in response to the current Climate Emergency.
We support the retention of the original historic windows, whilst utilising a secondary glazing system to improve their thermal performance. We emphasise the importance of both the retention of historic fabric and the reversibility of modern alterations, whilst improving the function and user comfort of the building.
We additionally support the use of external wall insulation and the removal of the previous detrimental application of a plastic lath and render. However, we have some concerns regarding the type of insulation proposed. We would recommend the use of natural and sustainable insulation solutions such as wood fibre boards over which a lime plaster skim finish could be applied; the use of permeable insulation will ensure the continued breathability of the external wall, lessening the future risk of emerging damp issues. We would further emphasise the importance of insulating around the window reveals with a lime plaster to prevent problems with condensation caused by thermal bridges.
Ultimately, we encourage the principle of the ‘whole house’ approach to energy efficiency which considers the contextual location and existing energy performance of a building, consequently resulting in a tailored retrofit approach that will be more effective in the long-term. With regards to historic buildings, their existing vapour permeability and natural ventilation should be maintained to ensure the optimum health and effectiveness of the building.