Heritage Retrofit

BCD SPECIAL REPORT ON HERITAGE RETROFIT FIRST ANNUAL EDITION 3 Analysis of the embodied energy and materials of historic buildings provides important indicators: • it prioritises a holistic evaluation of the long-term energy investment as well as performance in use of all older buildings • it broadens perception of the value of our built heritage beyond delimited cultural criteria to embrace environmental resource, societal factors and usefulness • it highlights the potential for mainstreaming retrofit measures beyond a restricted heritage sector, up-scaling traditional methods in tandem with appropriate new technologies • it facilitates the development of manifold options for balancing energy-related objectives with those of heritage significance, ones that are normal and affordable rather than specialist and expensive. In short, understanding sustainability requirements provides a major opportunity for the heritage sector to expand its field of activity and influence in concert with the mainstream retrofit sector. UNDERVALUED ENERGY PERFORMANCE An important starting point is to address negative assumptions regarding the energy performance of our existing building stock, especially older buildings constructed using traditional materials and techniques. The conventional criteria for identifying and calculating thermal performance across the built environment rely on simplistic thermal transmittance or U-values, ignore factors such as thermal inertia, and employ standardised and generally high assumptions concerning acceptable indoor temperature levels. The variation in performance as well as human comfort levels experienced between buildings of diverse constructional types is not taken into account, the behavioural patterns of building occupants as well as their tolerance of variabilities is ignored, and the results obtained from different energy certification systems – all of which are modelled theoretically – can vary significantly. The current measurement criteria combine to undervalue the thermal performance of older buildings and create an expectation that intensive levels of intervention are required to make them energy efficient, ones that anticipate conflict with their heritage significance while proving less effective than assumed. Additionally, there is no industry-agreed methodology for calculating and comparing the embodied materials and energy of diverse typologies of buildings by age and construction or of interventions into them, and life- cycle parameters and analyses are either neglected or poor. In 2007, based on research of energy consumption data across a broad cross-section of its building stock, the Ministry of Justice in England confounded preconceptions by demonstrating that its oldest, pre-1900 buildings use the least energy. The research also demonstrated that the performance of these older buildings was not approached in new construction until the 1990s and 2000s, decades during which energy use was still eight per cent higher per square metre than for the pre-1900 buildings. As the architect Jon Wallsgrove has written: ‘This innovative research... has shown that the conservation of our architectural heritage is directly compatible with energy conservation, rather than being diametrically opposed, as some environmental fundamentalists believe’. In the light of these and related findings both at home and abroad, priority has been attached by the historic environment agencies and others across the United Kingdom to the research and promotion of benign interventions and limiting detrimental impacts on the historic and traditional building stock. Notable in this regard is the ongoing applied research by Historic England (formerly English Heritage) and Historic Environment Scotland (formerly Historic Scotland), the Building Research Establishment, Changeworks, the Society for the Protection of Ancient Buildings (SPAB) and the Sustainable Traditional Buildings Alliance (STBA), and research conducted in historic cities including Bath, Bristol and Edinburgh. Austwick, Lancashire: house conversion. Heritage significance subsumes appearance and material fabric. In this case, whereas the material fabric has been retained by overlaying solar panels, the building’s appearance has been seriously compromised. Advances are being made in the production of solar roof tiles, also shingles and slates, which protect the overall as well as detailed appearance of historic buildings but require substitution of the fabric. The heritage impact methodology outlined in this article facilitates informed and transparent decision-making in situations where choices have to be made. (All photos: Dennis Rodwell) Thermal image composition showing heat loss from Bute House, Edinburgh (Image: Kal Murray, Eco Surveys)