5 North Parade Buildings, City Centre, Bath
5 North Parade Buildings forms part of a Grade II listed mid-18th century terrace of townhouses at 2-6 North Parade Buildings, now a mix of residential homes and offices, situated within the Bath Conservation Area and World Heritage Site. The terrace constitutes an early example of the architectural form and height used throughout Bath utilising Palladian elements such as Corinthian columns and triangular pediments over the front doors and first floor windows. No. 5 breaks away from the regular, homogenous form and layout of the terrace due to its internal subdivision to form two dwellings by 1799, resulting in the creation of No. 6 next door and a more modest front door treatment where there would have originally been a single pedimented door surround. Otherwise, this internal division has not affected the external symmetry and cohesive design of the buildings as part of the wider group value of the terrace.
In response to the Climate Emergency, BPT is supportive of the principle of retrofit works to improve the energy efficiency and thermal performance of Bath’s existing building stock, where this does not result in adverse impact to the special interest of a listed building or the character and appearance of the conservation area.
Internal Wall Insulation:
BPT welcomes the opportunity to consider the implementation of internal wall insulation within a listed building, where this can be sensitively relegated with the special qualities of the building, as well as being cohesive with the particular, porous material qualities of Bath stone to mitigate against interstitial moisture issues.
The Heritage Statement indicates a high level of retained architectural detailing across the ground, first, and second floors, including plasterwork cornices, panelling, door architraves and fireplaces. The existing timber panelling is indicated to be of historic value, with a number of features suggested to date to the subdivision of the property. Later 20th century interventions are evident as inserted cupboards and bookshelves on either sides of the fireplace at ground and first floors. There is also cited removal of internal fittings through the 1960s and 1970s.
The internal elevations as proposed do not indicate a change in appearance, where the existing panelling, coving, and skirting would be removed and replaced over the top of the proposed insulation layer. However, there is little indication as part of this application as to how the increased thickness of insulation would affect the appearance and character of the internal space, as well as further detailing such as how the insulation would intersect with the junctions between cornicing and floor, as well as navigating wall returns.
Where, or if, the existing panelling is understood to be of historic significance, there would be an amount of harm resulting from its removal of its original location and the ‘pushing forward’ of the external walls into the front and back rooms. This would need to be sufficiently weighed against demonstrated public benefits of improved thermal efficiency as part of a whole house approach to reduce energy use and carbon emissions. Based on Greengauge’s assessment, there is a question as to how effective the internal wall insulation would be; their heat balance table indicates that the approx. heat loss of the walls could be reduced from 35kwh/m2/yr to 30kwh/m2/yr.
Further details would be required to assess the specific suitability of internal wall insulation, such as a room survey/room data sheets to enable a close-range assessment of each internal elevation to be affected by proposals. A methodology of the proposed insulation instalment and reinstatement of historic finishes is also strongly recommended.
Windows:
As summarised in the Fenestration Audit, the windows to the rear of the property are described as “either modern replacements or substantially rebuilt in the 1960s.” The rear elevation features a mix of fenestration types, as well as a number of casement windows, indicating a varied and recent history of replacement. As such, the existing windows are of limited historic significance, and replacement would be acceptable in principle, where their replacements would be of an appropriate profile and traditional detail befitting the special architectural and historic interest of the listed building.
Where the existing windows to the rear are indicated to be non-historic, the principle of replacement would therefore result in NO loss of historic fabric and would have a negligible impact on the special interest of a listed building. We welcome the opportunity to install slimlite double glazed units where this would improve the thermal efficiency of the windows, reducing heat loss and associated carbon emissions, although maintain the need for further relevant details such as the provision of proposed window sections.
We are therefore supportive of the changes as proposed where this would ensure the sustainable use and continued occupation of a listed building whilst sustaining its special architectural and historic interest. Further identified benefits include the improved thermal comfort of residents and reduced heating costs, of particular relevance considering the ongoing cost of living crisis, as well as the broader contribution to B&NES Council’s net zero objectives. We do continue to recommend consideration of a ‘whole house’ approach to retrofit, considering a holistic package of interrelated behaviour changes and thermal improvements to ensure a more energy efficient performance.
In contrast, the windows to the front of the property are indicated to be 18th century, albeit potentially having undergone some restoration works in the 1960s, with the exception of the modern sash window at lower ground floor level as well as the 1960s dormer windows. The nature of these refurbishment works is not specified, and it is unclear as to whether any historic glazing has been retained across the principal façade of the building. The retention of glazing contemporary to the building’s original design and construction would be attributed high significance, and its removal would constitute harm to the special interest of a listed building which would require the clear demonstration of outweighing public benefit. We strongly recommend that the fabric and significance of the existing windows are further assessed and specified as part of this application to enable a better informed judgement of the scale of impact proposed to the building, and the resulting planning balance.
Further information is also required regarding the proposed interventions to the windows in the principal elevation; the application makes reference to the proposed use of “insulated glass such as Pilkington Spacia” to be fitted into the existing sash frames. Pilkington Spacia refers to a model of 6mm vacuum glazing, of which there are an increasing number of examples in Bath (see 12 Hanover Street, Circus Mansions, 13 Caroline Buildings). The design of this glazing incorporates 20 mm grid micro-pillars between the individual glazing panes, resulting in the windows having a ‘speckled’ appearance. We therefore have concerns as to how this glazing would appear within the principal frontage of a listed building, and the wider grouped setting of the terrace. Where this model of glazing is proposed, there is a need for further assessment of visual impact as part of this application, potentially utilising a glazing sample or the installation of a ‘trial’ window with the support of the case officer. BPT would be very interested in engaging further with the applicant with the possibility of a site visit to see the proposed vacuum glazing in situ.
Air Source Heat Pump & Vaults:
The opportunity to replace the existing gas boiler with an ASHP would be positive in principle, where ASHPs are more energy efficient. Where installation is considered as part of a ‘whole house’ retrofit approach, the total energy demand of a household is reduced and as such further diminishes the level of energy generation required and any resulting carbon emissions.
BPT is generally encouraging of ASHP installation where these can be sensitively integrated with the occupation of a listed building, particularly in establishing opportunities for suitable installation locations and measures that could be implemented more widely through Bath’s terraced housing typology which share a number of distinctive features, such as below-pavement vaults and cellars.
We have some questions regarding the suitability of the vaults for the proposed ASHP in ensuring adequate levels of ventilation to the unit, as well as how effectively any associated noise would be mitigated (eg. through the selection of an ASHP model with a quieter operational volume, acoustic insulation, etc.). As subterranean spaces, vaults are typically damp and poorly ventilated, and are not easily altered to facilitate passive ventilation or air movement. Where Greengauge has recommended installation of the ASHP within the vaults, this does however indicate an expectation that a unit would function successfully in this space, and BPT would be interested in discussing this further with the agents to better understand the justification and technical specifications for the use of the vaults, which could be more widely applied in Bath.
With regards to the proposed treatment of the vaults, BPT generally takes a position against the conversion of vaults for residential purposes, where these spaces are typically incompatible with the dark, damp, and ill-ventilated qualities of Bath’s vaults and cellars. In this case, the vaults would remain in a use subservient to the main residential function of the house, functioning as storage and a plant room, and as such this use would be acceptable. Where excessive levels of damp are preventing certain uses ancillary to domestic occupation, such as storage, acceptable mechanical methods of damp proofing would include dry lining and membrane lining systems, although this would remain dependent on whether lining would compromise any internal features of interest which should be clarified as part of the application.
Where it is recognised that the application of a dry lining membrane system may result in some minor adverse harm to a listed building where this may conceal historic stonework or alter the appearance and character of the space, this should be considered in balance with the benefits of bringing the space back into an appropriate, ancillary use, and facilitating the low carbon retrofit of a listed building.
Mechanical Ventilation Heat Recovery System (MVHR):
As part of the Energy Strategy submitted by Greengauge, it was recommended to install MVHR to ensure an appropriate level of ventilation to ensure the viability of installing the ASHP, as well as securing an appropriate level of internal relative humidity to mitigate hydrothermal risk. It was proposed to install a MVHR system at third floor level; “supply and extract ducts will drop vertically and branch at each floor level.” A plant room is indicated at third floor level, but no further information is supplied regarding the proposed installation of MVHR. We therefore recommend that this aspect of proposals is clarified; where a MVHR system would be installed, further details are required regarding how the system would be installed throughout the building and how this would interact with internal historic fabric.
Next Steps:
• We would be happy to provide advice and comment further on the internal fabric and approaches to insulation.
• We would welcome a site visit and meeting with Greengauge to better understand the approach to the proposed ASHP.
• BPT would welcome the opportunity to monitor and share approaches to high quality energy efficiency retrofits and would be enthusiastic to create a case study on the approaches and measures used at this property subject to listed building consent approval and the owner’s permission.