Bath Preservation Trust does not normally comment on the specifics of internal alterations to private residential properties. This is because in most cases it would be difficult to make a proper assessment based on documentary evidence alone; site visits are often necessary and access to private property is limited. However, the number of recent planning applications for conversion of vaults to living accommodation has prompted this position statement.
Underground vaults are integral to the design of many 18th and 19th century houses in Bath. As such, they are an important element contributing to the architectural and historic significance of listed buildings and the historic townscape. Vaults, basements and cellars constructed in porous Bath stone may over time suffer some degree of damp, but the severity of this very much depends on the external circumstances. In The London Terraced House (1756), Isaac Ware writes on the subject of vaults: “the lower story in these common houses in London is sunk entirely underground, for which reason it is damp, unwholesome and uncomfortable” (p.346).
BPT has an ‘in principle’ objection to the conversion of damp vaults for residential uses. Trying to achieve 21st century living standards in an 18th century below ground room is removed from conservation principles. This part of a building is best used for ancillary facilities or storage space to serve the habitable areas of the house, as originally intended.
Vaults are not fit places for the core activities of human habitation, such as sleeping, working or relaxation, and we would not be easily persuaded by any argument that seeks to justify a use that could be easily and more appropriately provided elsewhere within a property.
Even where vaults are relatively damp free, they will not normally be suitable for residential use, as levels of daylight and outlook will be substandard and not able to be ameliorated without damage to the historic fabric.
We recognise that in many cases, damp can be managed with limited intervention so that underground spaces can be used for some ancillary uses. The simplest and least intrusive approach is to use a lime plaster on internal wall surfaces, and ‘limecrete’ type products for floors, provided that internal features of interest, such as pennant floors, are not compromised. Modern acrylic and emulsion paints should never be used because they are impermeable and trap moisture which causes further damp.
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; again, this is provided that internal features of interest are not compromised.
BPT does not support methods such as chemical injection or cementitious tanking. These impermeable materials do not allow the permeable traditional building fabric to breath or moisture to pass through; thus, moisture is displaced or trapped and frequently this can lead to problems elsewhere (especially if tanking is applied externally). In addition, these approaches have a short life span and are known to fail over the passage of time.
The frowsty conditions of underground vaults are part of the character of an older house; the vaults are often the least altered area of the building, and may contain valuable historic fabric, evidence of the story of the house, such as stone water tanks, sinks and wine bins. Unless the structural stability is in question, it is best to leave well alone. As with rot, always aim to treat the cause rather than the symptoms. Damp proof courses, water-repellent solutions and plastic type wall coatings do more harm than good when inappropriately applied to buildings.
Where assistance is required, consult an independent professional, such as a chartered surveyor, rather than a damp-proofing remedial company with a vested interest in their own recommendations.
You can read B&NES Council’s Planning Guidance Note on Historic Vaults in Bath for further planning recommendations.