20 Sion Hill, Lansdown, Bath
20 Sion Hill is a Grade II early 19th century detached villa, situated within the Bath City-Wide Conservation area and World Heritage Site. It is positioned adjacent to a run of Grade II late 18th – early 19th century dwellings to the east at 16-19 Sion Hill and forms the wider, indicative streetscape setting for a number of Grade II detached and terraced dwellings further along Sion Hill towards Cavendish Road.
BPT acknowledges the difficulty of managing vaults as typically poorly ventilated spaces, and we recognise that these may be susceptible to multiple forms of water ingress/damp, including run-off from the pavement above, which can be complex to address.
The basement and vaults have been subject to unauthorised tanking works with the application of a cementitious render in two of the vaults and the ‘playroom’ within the main footprint of the building. The Method Statement describes the current condition of the space as follows: “The existing condition of the vaults is satisfactory, there are no damp issues in the majority of spaces.” The cement-based tanking system has been indicated to fail in Vault B03.
We are supportive of the applicant’s endeavours to address the unauthorised works to the basement level and consider more sympathetic measures in relation to the special interest of the listed building.
Where possible, BPT expresses a strong preference against the use of cement-based waterproofing works where this would be incompatible with historic fabric and harmful to the special interest of a listed building. Where possible, we encourage consideration of its removal to allow the underlying stonework to breathe; however, in this instance it has been evidenced within the Method Statement that the removal of the cement layer would result in unavoidable stone damage. In the planning balance, it may therefore be considered that there would be greater harm to historic fabric from the cement render’s removal, which may therefore justify its retention, though we consider that this intervention should not be considered to be authorised as part of this application.
Where it is proposed to replace the area of failed cement tanking with “rigid plastic membrane such as the Newton 500 system”, we question the justification for the introduction of further waterproofing measures. We encourage the opportunity to retain the exposed stonework where the cement render has already failed to better allow it to breathe, with necessary damp mitigation measures such as a lime wash (or a lime render in cases of more severe water ingress) being more sympathetic to historic fabric. The existing condition of the basement is indicated to be fairly dry with no notable damp issues, without clear indication as to whether this can be solely attributable to the cement waterproofing intervention or not. We therefore encourage the failed render to be removed to allow the natural stone surface to be restored, and where necessary to dry out, and then re-assess what damp mitigation works may be most appropriate.