Historic plaster is an interesting feature of old buildings and should not be removed merely to expose the stonework, brick or timber-framed structure beneath that was never intended to be seen. Nor should plaster or render be removed because it looks old. Unless plaster or render is failing and that failure is causing damage to the building and can cannot be repaired in situ, it should be retained. Not only is the 'do nothing' approach the most economically effective, but historic surfaces have a unique patina which has formed over time. This patina is integral to the character and interest of historic buildings and should be respected.

Where it can be demonstrated that render or plaster does have to be replaced then traditional lime-based render should be used (unless the original render is itself cementitious). Due to its impermeability cement render is incompatible with buildings constructed out of traditional materials as it prevents any moisture within the wall from evaporating. Over time this trapped moisture will cause the wall surface to deteriorate and spall beneath the render. The use of cement based renders is highly unlikely to be acceptable at application stage.

Other historic renders such as stucco and Roman cement should be replaced and repaired like for like as they have a distinct appearance; they create smooth surfaces and allow for sharp edges often used to imitate ashlar stonework.

When re-rendering it is crucial that architectural decorative features are not obscured or concealed under the new render. Stuccoed elevations will often imitate mock jointing, rustication or plaster elements such as cornices. These should be retained or carefully copied using the traditional techniques to do so. Similarly, decorative plaster details such as pargetting and scraffito should not be removed or concealed under new render. The historic and architectural interest of both of these decorative techniques are such that any proposals to do so are likely to be strongly resisted.

In some circumstances the painting or repainting of a listed building will require consent, namely when the proposals would have an adverse impact on the special interest of the building by altering its character or appearance. As with render, cement based or or the impermeable or gloss paints should not be used on traditional buildings due to their impermeability. The correct finish for historic renders and plasters in lime-wash.

Where inappropriate renders or paints have been applied to the exterior of a building expert advice should be sought before any works are undertaken to remove it as doing so could cause catastrophic damage to the surface of the building.

It is important to note that whilst repainting with lead-based paints may be historically correct this activity is now restricted to Grade II* and Grade I listed buildings and must be referred to Historic England.

The roof is often the most dominant feature of a building and every effort should be made to retain its original structure, pitch, cladding material and ornament. Whilst a roof has a very important structural and protective role to play, they often have architecturally interesting qualities as well. For example the pattern and coursing of different stone and slate tiles varies regionally and nationally and the difference in roofing materials from clay to slate and thatch to stone is a distinguishing feature of different building types and areas of the country. Where traditional and/or local roofing materials exist their retention should be priority. Should the roof need to be stripped as much of the original roofing material should be re-used.

The addition of new dormers and rooflights to an historic roof must be approached carefully. The existing historic roof structure should not be damaged in order to facilitate a either option and is likely to only be acceptable where they are least visible and do not compromise the special interest of the building. It is important to consider the impact of new dormers and rooflights on historic terraces: should proposals for either disrupt the symmetry design, it is likely they would harm the special architectural interest of the group.

The internal features one finds in a historic building, including staircases, joinery such as window shutters, doors and doorcases, panelling, decorative mouldings and ceilings, stucco-work, chimneypieces and wall decorations and paintings all come together to form the special interest of a building and may be its most significant feature. The removal or erasure of any of these features is unlikely to be acceptable.

Even where buildings are not highly decorative they likely contain historic joinery and plasterwork which speak of the materials and construction of the time the building was built. All original plasterwork should be repaired and retained wherever possible and great care should be taken where new services are proposed. Chasing in wiring to historic plaster is unlikely to be acceptable especially where it is highly decorative or painted.

In many cases the basement may be one of the few parts of the building that has not seen a great deal of alteration and, as such, it provides valuable evidence of the building’s original plan form, history and development. Basements may also be one of the last areas to retain any surviving original finishes, which should therefore be protected and retained rather than destroyed.

In The London Terraced House (1756), Isaac Ware writes on the subject of basements and 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). This is a description of the very necessary nature of these spaces as they are designed to allow for the passage of moisture through the building. The conversion of damp vaults and basements for residential use is difficult to achieve without an inappropriate level of intervention into a building, and in most cases the SPAB would not support such proposals. Even where vaults are relatively damp free, issues of natural light and outlook are likely to be at play and preclude basements from being fit spaces for core living purposes. These spaces were designed to be ancillary to the habitable spaces of a house and to change the nature of that space for human habitation is likely to go against the SPAB approach.

Where basements and vaults are too damp to fulfill their purpose as ancillary storage space we accept that damp can be managed with limited intervention. The simplest and least intrusive approach is to use a lime plaster on internal wall surface and a limecrete product to the floor, provided that any features of special interest are retained and not harmed in doing so. However, it is also important to consider that excessive damp is often a symptom of problems of water ingress and rather than treating the symptom the cause should be full understood and the appropriate action taken.

The SPAB does not support damp treatment methods such as chemical injection or cementitious tanking. These impermeable 'solutions' are not compatible with traditional, permeable building materials as they do not allow for the passage of moisture through the building. It is likely that moisture will become trapped in the building's fabric or be displaced elsewhere.

Original and historic shopfronts add a great deal of character and architectural interest to individual buildings and to the wider streetscape. Wherever shopfronts of architectural and historic interest remain they should be repaired and retained rather than replaced. Features of shopfronts from the 18th and 19th century (and perhaps even the 20th century) may be concealed under more contemporary shopfronts and so where works to modern shopfronts in historic buildings are proposed, the potential for survival of features should be borne in mind and works undertaken carefully. Where a new shopfront is required it should be designed in sympathy with the rest of the elevation it is to occupy.

The issue of excavating basements under London townhouses has been a hot topic in conservation circles in London for some time and we expect this trend will become more widespread. The SPAB is concerned that excavating beneath a property to create a new or extended basement will have a profound impact upon the historic fabric and character of the heritage asset and also on the legibility of the building’s development and hierarchy of spaces, even though the changes will not be very visible other than from within the basement itself.

The SPAB also takes the view that traditional buildings have an intimate connection with the land on which they are constructed and the relationship between the building and the ground below its foundations should not be lightly dismissed. Excavating beneath the ground floor of the building breaks this intrinsic and important connection with the land and would result in a building that is no longer in its original context, and should therefore be firmly resisted.

There are, of course, also a whole host of related and very serious technical concerns regarding the physical impact on the neighboring properties. It is extremely difficult to predict accurately how such a large and invasive excavation might affect the water table and the movement of water within the ground around a property, but it seems likely that there is at least some level of risk to the building and to any neighboring structures.

The SPAB is also concerned about the introduction of additional light wells, as these will inevitably change the appearance of the outside of the building and will have an adverse impact on its setting due to the light that will wash upwards across the elevations when the lights are used in the basement in the evening.

The Royal Borough of Kensington and Chelsea has adopted a new local planning policy (CL7) which indicates that basement developments should not extend under listed properties. The SPAB wholeheartedly endorses this policy and hopes to see a similar approach taken in the other London boroughs and authorities nationally in due course.