Conservation means ‘minimum intervention’
Lee Meadowcraft is conservation professional and member of the Institute of Historic Building Conservation, He maintains that he is bound by the fundamental principles of minimum intervention, reversibility and like-for-like repair. On 26 February 2015, he posted that specifically, what is meant by minimum intervention and how it can be applied to building projects in order to retain historical significance during works of repair, maintenance and adaption is the conservation principles based on an unequivocal respect for historic building fabric. All work that has the potential to cause harm to that fabric requires a cautious approach of "changing as much as necessary but as little as possible" (Burra Charter, ICOMOS, 2013).
Conservation principles, writes Meadowcraft, are established in English law through British Standard 7913 - Guide to the conservation of historic buildings and the National Planning Policy Framework (NPPF). BS 7913 and the NPPF recognise that interventions (physical changes to original materials) are not only necessary for historic buildings in order to maintain the asset in a good state of repair, but are often desirable to ensure a building is kept fit for purpose and in regular use. Adaptive re-use of buildings requires careful management of change based on a detailed understanding of the fabric and its historical significance. Often there is a desire to improve the performance of historic buildings to enable economic development for new use or to respond to changes in building legislation. Minimum intervention design is an essential tool for all professionals involved in the design and specification of repair and maintenance works, development and change of use of historic buildings.
In practical terms, what Meadowcraft professes is the default starting position for all works to historic buildings should be to prioritise the retention of historic fabric in its original location and only carry out alterations or removal of fabric if there is "clear and convincing justification" for doing so. The option of doing nothing at all should always be a consideration. Sound conservation solutions require the designer to adopt a deliberate conservation-minded approach to design and specification in place of a more traditional cost-driven approach, whilst also recognising the commercial needs of the client.
Where existing fabric is damaged or decayed, writes Meadowcraft, the minimum amount should be removed as is practically possible to allow a repair to be undertaken. This means for example, that where timber decay is evident, only that part of the timber that is decayed should be removed with new timber spliced to the existing using traditional carpentry repair methods. Wherever possible, repairs and strengthening works should use traditional skills and materials rather than modern interventions - only using new materials resulting from changes of load paths.
Meadowcraft emphasises that the principal of minimum intervention can be applied not only to historic buildings but for all works to existing buildings. Often it can be more economic, quicker and safer to reduce interventions in to existing fabric in order to retain sound and stable conditions. It is often necessary to go the extra mile to prove existing building fabric is sound or suitable for re-use but the benefits to the building and its stakeholders means the extra time spent is seldom time wasted.
Meadowcraft’s point is salient in many conversations and policy reviews of approach. Certainly, his precautionary approach is echoed in the Burra Charter and corresponding guidelines in the English jurisdiction such as; the National Planning Policy Framework (NPPF) and BS 7913. As subtle as these guidelines are, they are rarely taken seriously by architects and designers who often regard Heritage as a kind of party pooper i.e. leading the “good ship design” into treacherous waters by imposing too many prohibitions. The point is that changes made to heritage buildings can never be reversed if fabric is removed or the imposition of adaptive re-use is too great. We effectively only ever get one good go at it. As conservators, we must be more vigilant and we must evolve design approaches that meet the client’s needs while not being overly injurious to original building fabric.
Paul Rappoport - Heritage 21 - 13 March 2015