One of a series of guides for those working with architects published by Granta Architects.
Conservation aims to preserve the fabric of an old building in a way that is appropriate to the continuing use of the building. This rarely means that it is simply restored to its original condition. The building must accommodate the requirements of its current and future occupants, including modern services and utilities, insulation and sustainable living and working. Listed buildings must be changed only in line with planning regulations dictating their evolution.
Conservation planning takes account of the needs of the historic environment and of the occupants of a building to plan development in line with both national and local guidelines and legislation. Listed buildings (grades I, II and II*) are subject to the Planning (Listed Buildings and Conservation Areas) Act 1990 which governs development, alteration and renovation. The Planning Policy Guidance Note 15: Planning and the Historic Environment (PPG15) offers guidance on the development of listed buildings. Around 2% of the dwellings in England are listed.
Substantial work on a major listed building generally starts with a conservation plan. In the plan, we set out the current state of the building and comment on its use and any modifications that have taken place since its original construction.
The plan will address the materials used in construction and any later development, damage to the structure or fabric, and aspects of the building’s use which will have an impact on how it will be developed or restored.
Over time, the original fabric and structure of a building may deteriorate or the building may become unstable. The ground beneath a building may rise (heave) or fall (subside) and may also distort horizontally. This can cause cracks and distortion and may make the building unsafe.
Timbers shrink by about 15mm along their length in 100 years, so the end bearing of rafters and joists must be checked.
Signs that the ground may have moved under a building include an uneven roof line, structural cracks in the wall, and sagging or slanting windows or brickwork. Traditional underpinning involves spreading the load of the building by strengthening the foundations, but is often not necessary and is rarely the best solution.
When an extension or new building is constructed next to an existing building, there will inevitably be ground movement, and this must be allowed for. In the case of an old building with a stable structure, but which cannot take additional load, an inner timber frame may be tied to the existing framework. The space between the new and original frameworks allows for insulation of the walls.
Old lime mortars and timber-framing allowed seasonal movement of buildings. Modern cements are so hard that they cannot accommodate movement and can lead to more problems for a building.
Working on a listed building involves sensitivity to the materials used in the original building and a good historic knowledge of appropriate materials. Building materials have changed considerably over the centuries, and work on a listed building often involves dealing with materials that are no longer used. Repairs must be made using appropriate substitutes.
Thatch was a common roofing material in the UK until the end of the First World War, and Britain has more thatched roofs than anywhere else in Europe. Thatch is vegetation — often straw, sedge or water reed. Traditionally, straw thatch is renewed by layering new thatch on top of the old, leading to some roofs with a layer of thatch two metres thick and dating back 600 years. Rethatching is necessary around every 50 years, with re-ridging around every 15 years.
Old walls may be made of wattle and daub, a mix mud, clay or even animal dung mixed with horsehair, spread over a latticework of split sticks. The technique has been used for at least 6,000 years. We can remove and re-use wattle, mixing with fresh water and supplementing with lime and fresh dung!
Granta Architects works with private individuals, corporate clients and public sector bodies to produce sustainable developments fully compliant with the requirements of conservation. We are always sensitive to the architectural and natural environment as well as to the needs of the client.
Published by Granta Architects Ltd, 12D Kings Parade, Cambridge, CB2 1SJ
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