Flat 4, Circus Mansions, 36 Brock Street, City Centre, Bath

36 Brock Street is a Grade I mid-18th century terraced townhouse designed by John Wood the Elder, situated within the Bath conservation area and World Heritage Site. It forms the immediate, adjoining context of the Grade I Circus, one of Bath’s monumental residential constructions with intentional sightlines to the Royal Crescent via Brock Street and down into the city centre via Gay Street, and remains a grand example of the Georgian Town Planning and Georgian Architecture, attributes recognised as of Outstanding Universal Value.

In light of the declared Climate Emergency, BPT is supportive of sensitive sustainability retrofits, where deemed appropriate, within the historic environment, as well as the sympathetic upgrade of traditional and listed housing stock to better meet modern standards of living. As such, we therefore note a positive opportunity for the sensitive implementation of energy efficiency retrofits and thermal improvements where this does not result in harm or the loss of significant historic fabric.

We appreciate that there are very few examples of ultra-slim double glazing such as vacuum glazing, with glazing of this type having recently been granted consent at 12 Hanover Street (see 22/01230/LBA). We therefore welcome the opportunity to trial updated glazing models that allow for the possibility of a much reduced profile thickness alongside improved thermal performance. However, this remains to be appropriately balanced against possible visual impact to a listed building.

The rear elevation of the building is of restricted public visibility, with publicly accessible views limited to Circus Place. The addition of slimlite double glazing to the rear elevation would therefore be of reduced visual impact. Whilst we note that there is a missed opportunity to coordinate with the other flats in the building to ensure a coherent fenestration treatment to the rear elevation, the terrace rear is characterised by its varied and eclectic character in which there are a diverse range of fenestration types. We also consider that this could be an opportunity to encourage further, future schemes for the reinstatement of traditional 6-over-6 glazing across the other floors of the building.

We are supportive of the reinstatement of a traditional 6-over-6 sash profile in keeping with the original window fenestration of the listed building and its wider terraced setting. The existing glazing panes are indicated to be later insertions due to evidence of the removal of earlier glazing bars, and therefore their replacement is not opposed where this would not constitute a loss of historic fabric.

The proposed vacuum glazing is indicated in the existing and proposed sections to be of a matching thickness to the existing single glazing (6mm). It is therefore presumed that there would be minimal material alterations required to the box frame to accommodate the new glazing, although we recommend submission of further detail as necessary regarding possible alterations required, such as accounting for any weight/balance changes between the sashes.
However, we maintain some concerns regarding this type of glazing and possible visual impact to a Grade I listed building. The technical specifications of Fineo glazing includes reference to the use of “20 mm grid micro-pillars” between the individual glazing panes, which may result in the windows having a ‘speckled’ appearance and detract from the overall appearance of the listed building. We maintain that greater consideration of how this glazing would appear in situ and how the appearance of the internal support pillars may be suitably mitigated is required. The submission of a relevant sample would be welcomed.

Therefore, whilst we are supportive of the principle of this scheme and welcome the opportunity to trial new thermally-efficient retrofits in Bath’s historic housing stock, there is currently inadequate information to assess how the special interest of the listed building and the character and appearance of the conservation area would be affected.

BPT is very interested in working with the applicant to reach an acceptable solution and to assess the performance of the windows before and after retrofit to create a ‘best practice’ case study. This information could then be used to more accurately assess the suitability of slim and vacuum double glazing installation in Bath’s historic building stock, and inform future upgrades of listed buildings.