21 Dafford Street, Larkhall, Bath
21 Dafford Street forms part of a Grade II early to mid-19th century terrace situated in the Bath conservation area and World Heritage Site. The terrace is made up of modest two-storey double-depth houses stepped down the west-east slope in pairs. There is a mix of window types used along the terrace, with a lot of dwellings having replaced a traditional 6-over-6 sash profile with a Victorian 1-over-1 sash profile. 21 Dafford Street has similarly had its windows replaced with 1-over-1 single glazed sashes, in an aluminium frame which is of detriment to the appearance and material vernacular of the listed building and the group value of the terrace. It has additionally had its traditional 6-pane timber door removed, examples of which are still common across the terrace, and replaced with a Victorian-style alternative.
In principle, BPT is supportive of sensitive sustainability retrofits, where deemed appropriate, within the historic environment. Our position in a relation to the appropriateness of a range of measures is set out in our publication Warmer Bath: A Guide to Improving the Energy Efficiency of Traditional Homes in the City of Bath. In light of the current Climate Emergency, we appreciate the urgency of reducing energy consumption and carbon production, as well as upgrading our existing historic housing stock to meet modern standards of living and thermal performance.
However, the suitability of energy-efficient retrofits in relation to heritage significance, effectiveness, and the risk of unintended consequences must be assessed on a case-by-case basis.
In this particular case we recognise this proposal would result in less than substantial harm and no loss of historic fabric. The existing aluminium-framed sash windows are of detriment to the appearance of a listed building, and their replacement with a more traditional timber alternative would be a heritage gain. We welcome the opportunity for the reinstatement of a more traditional 6-over-6 sash profile in keeping with the building’s original historic appearance.
We note that measurements of the windows as existing have not been provided, and therefore the extent of change proposed by this application remains unclear. There are no existing window details, close up photographs or measured sections against which the proposed sections can be compared. We would therefore recommend that sections of the existing windows are submitted for clarity.
However, we have concerns about the glazing bar thickness proposed, particularly the thickness of the meeting rails and bottom rail. The meeting rails appear to meet vertically, rather than featuring a more traditional angled meet. We emphasise the need to consider an appropriately slim glazing bar to avoid the proposed windows looking overly chunky or heavy within a terrace of relatively fine, albeit non-historic, fenestration.
We question the appropriateness of the glazing bar profile proposed. Given the age of the original building an ovolo profile could be considered more appropriate. This might be a good opportunity to reinstate this historic profile.
BPT is very interested in working with the applicant to reach an acceptable solution and getting better understanding of the existing window condition and design. It could help provide an invaluable opportunity to monitor the thermal and acoustic efficiency of the windows, before and after, whilst also observing any additional repercussions such as changes in humidity levels. This information could then be used to more accurately assess the suitability of slimlite installation in Bath’s historic building stock.
The Trust acknowledges this scheme’s potential to establish a precedent for the installation of windows with higher energy efficiency within Bath’s listed buildings, with a resulting effect on the aesthetic, architectural, and historic integrity of Bath’s historic environment. Therefore, we feel that if proposal such as this could be got right, and before and after data collected to evidence improvements in efficiency, it could be used as a best practice example that would help further future retrofits to buildings of historic significance within Bath.