7 Duke Street, City Centre
7 Duke Street forms part of a Grade I Georgian terrace within the core of the Bath conservation area and World Heritage site. It forms part of a highly significant streetscape made up from a high density of Grade I terraces such as North Parade, South Parade, the Georgian House, and Pratt’s Hotel. Consequently, its is if high architectural and aesthetic value in its location within an area of high evidential value, encapsulating the original Georgian plan form designed by John Wood the Elder.
BPT supports the replacement of asbestos slates and gutters with natural alternatives. The use of natural slate and lead fixtures is in-keeping with the original aesthetic of an historic traditional building, and therefore enhances its appearance and function. We feel this also offers a beneficial opportunity to conduct additional maintenance works such as the replacement of faulty roof tiles, clearing of gutters, and ensuring that the roof is watertight to coincide with the proposed installation of a breathable roof membrane.
We further support the proposed cleaning and paint removal from the front-facing façade. This will further enhance the appearance of the listed building and conservation area, and improve the setting of other adjacent Grade I properties. The existing stonework is stained and in need of cleaning of low-pressure cleaning by heritage professionals to positively restore an aesthetic and architectural uniformity across the Grade I terrace of Duke Street.
However, we would urge the LPA to request more information regarding the types of insulation that have been selected for use, and where exactly in the roof space they will be installed. Whilst rockwool insulation is vapour permeable and therefore suitable for use within historic buildings, it is low-performance when damp and takes a long time to dry. We would recommendthat a natural wool or cellulose option is considered as a high performance, sensitive, and sustainable option.
With regards to the use of Celotex in the mansard roof slopes, we would advise that a more suitable form of insulation is used. Foil-based rigid insulation is often unsuited to historic buildings due to their use as a vapour barrier that can result in a build-up of condensation, as well as the difficulty of installation around roof rafters. The Trust would advocate the use of a more suitable natural fibre insulation such as wool or hemp; these are more sustainable options that are also capable of absorbing excess moisture whilst maintaining a consistent thermal performance. Loose insulation is additionally better suited to being installed around rafters and minimising any potential thermal bridges that can exacerbate existing moisture problems. We would ultimately need more information regarding the existing state of the roof space to determine whether Celotex is an appropriate choice, to ensure full compatibility with the historic fabric of a Grade I building.
Finally, whilst the Trust supports the replacement of the existing, poor condition dormer windows in a like-for-like style, we would encourage the use of slimlineglazing rather than single glazing to ensure an improved thermal performance in light of the current Climate Emergency, we would encourage positive retrofitting measure to improve the building’s energy performance. For example we feel that the use of slimline timber double glazing at dormer level will have a negligible aesthetic impact on the building’s façade, and will not result in any detriment to historic fabric. If considered along with ventilation, it may help building’s improved residential function and comfort whilst helping to lower energy consumption.
Therefore, BPT supports the positive remedial works to the exterior of 7 Duke Street. We feel that the special architectural and aesthetic interest of the terrace will be enhanced, and consequently this will enhance the traditional appearance of the Bath conservation area. However, due to the Grade I status of the building, we do not consider enough information has been submitted regarding the use of insulation and its suitability within the roof space.