Historic buildings vary greatly in how much they can accommodate change without losing their special interest. Some are sensitive to the slightest alteration, especially externally, or where they have important interiors, fixtures, fittings or other detailing. Others may already have changed significantly during their lifetime and can accommodate further change relatively comfortably. These considerations will influence the extent of change that is appropriate when looking at potential alterations to respond to climate change impacts or energy efficiency measures.
An early dialogue between the owners/occupiers, designers, building control surveyors, development control officers and conservation officers is usually to everyone’s advantage.
Before considering any alteration, it is important to assess the elements that make up ‘significance’: the special character and interest of the building.
Significance depends on:
- External features including decorative façades, roof details, windows and doors.
- Plan and internal layout is one of its most important characteristics. Interior plans should be respected.
- Internal features of interest such as decorated plaster surfaces, panelling, floors, window shutters, doors and doorcases.
- Details such as mouldings, stucco-work, wall and ceiling decorations can be just as valuable in simple vernacular and functional buildings as in grander architecture, and can be a building’s most important feature.
Once significance has been assessed, a ‘Conservation Statement’ or ‘Conservation Plan’ can be written which sets out why the building is significant and how that significance will be retained in any future use, alteration, development or management. For many simple buildings this may be little more than a list of features. A Conservation Plan is therefore not a plan of works, but it is important for shaping current and future plans of work.
An understanding of what constitutes the special interest of a historic building requires experience. If there is any doubt, consultation with a local authority conservation officer is recommended.
Regular inspection and maintenance is vital and the first step in improving energy efficiency and maintaining the building’s ability to withstand extreme weather. A damp wall caused by a blocked gutter will be colder and loose more heat. Slipped tiles allow cold draughts. Ivy on walls reduces solar gain as well as exacerbating damp by preventing evaporation from the wall surface and leading to loss of pointing through root action. Flaking paintwork on windows allows in water that causes warping and then draughtiness.
Before repair, the cause of the problem must be identified and dealt with as far as possible: treating symptoms (a damp wall) without addressing the cause (a leaking down-pipe) is pointless. If new materials or detailing are introduced, these should match the original as closely as possible, unless flaws in the original construction have caused problems.
Some buildings, or parts of buildings, are of such quality, importance or completeness that they should not be altered at all save in the most exceptional circumstances.
Find out whether the building is listed or in a conservation area. Also check with the local planning authority to see if other planning conditions are in place (e.g. if the building is in an area of outstanding natural beauty, or if an Article 4 direction, which restricts certain permitted development rights, covers the building). The local planning authority will be able to explain the implications of such conditions. Check what consents are required and obtain them before starting any work.
It is important to understand the current energy performance of the building, before taking any measures to improve it. For example, if it is cold because of air infiltration, adding extra insulation to the loft will be pointless. If a building is already airtight, adding extra draught-proofing may lead to problems of condensation, and the need to open windows for ventilation. If a building is known to be draughty the source(s) of the draughts should be identified – draught-proofing windows and doors may be wasteful if the source of draughts is through the floor or walls.
Many traditional buildings were built using soft, flexible or permeable materials, such as mortars, plasters, renders and paints. These allow the fabric to respond to air, moisture and structural movement in a way that is fundamentally different to the hard, rigid, impervious materials and membranes widely used in modern construction.
Alterations should be compatible with the fabric that is being altered to enable the existing fabric to perform as intended, and to prevent problems at the interface between types of fabric. Modern methods and materials that would be effective and appropriate on a new building may be ineffective and cause sequential damage in a traditional building. Examples include the use of cement or gypsum based mixes for plasters, renders and pointing where incompatibilities in flexural strength, permeability and porosity can lead to disastrous salt migration and damage.
A fundamental principle is to minimise any intervention into the historic fabric of the building. The stock of historic buildings is finite and every loss or major alteration to fabric is significant. The losses of even small pieces of fabric add up over the long lives of old buildings. Piecemeal replacement of components diminishes the value of the remainder.
Even replacement of original materials on a like-for-like basis will cause the loss of historic evidence in the original fabric. For example even the most careful replacement of partially decayed beams with new beams in a traditional manner will affect appearance and result in the loss of much of the building’s history.
If possible alterations should be designed in such a way that they can be reversed without damaging the existing fabric. This is especially pertinent where the changes are to building services which are rapidly evolving technologies and have correspondingly short lifetimes.
It is good practice to minimise future interventions by using good quality materials and workmanship; only make changes that are proven to be effective, and use materials that have proven performance. Proprietary products that will need special parts to repair and maintain should be avoided, these parts may not be available in future.
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