Heritage Retrofit

BCD SPECIAL REPORT ON HERITAGE RETROFIT FIRST ANNUAL EDITION 15 THE STANDARD ASSESSMENT PROCEDURE – RDSAP and SAP The most common detrimental tool imposed on domestic traditional buildings is RdSAP – the reduced data standard assessment procedure – which was the basis for advice provided under the UK government’s failed financial incentive scheme, the Green Deal. Today its most common use is in producing energy performance certificates (EPCs) when a dwelling is being let or sold, unless it is listed. RdSAP will almost always underestimate the current energy efficiency of a traditional building and therefore make recommendations for works which are not necessary and which may not make a building more energy efficient. There are a number of reasons why this is the case, but the main one concerns the standardisation of U-values which normally results in the thermal performance of traditional construction being underestimated. It becomes a serious concern when this results in inappropriate measures being deployed. Despite these well-known flaws, the imposition of RdSAP is being taken a stage further. The Private Rented Sector Energy Efficiency Regulations (Domestic) dictate that by April 2018 residential properties cannot be let unless they reach energy performance rating band E. Property owners may have to undertake works which deliver SAP points determined by RdSAP. There is no reward, however, for maintaining buildings properly and appropriately and keeping building fabric dry, all of which help to make buildings far more energy efficient and sustainable. BREEAM and BREDEM The Building Research Establishment’s environmental assessment method (BREEAM) for the refurbishment of domestic buildings contains some very good practice in considering a range of issues, but where energy is concerned it is flawed in using RdSAP for the reasons stated above. Another version of BREEAM has been developed for the refurbishment of non-domestic buildings where research by BRE has established that heritage buildings do relatively well. However, while RdSAP is not part of this process, the full version of SAP is, and again the standardisation of performance data (such as the U-values of existing walls) results in inevitable inaccuracy where energy performance is concerned. The BREDEM (BRE Domestic Energy Model) is also based on SAP, hence its potential unreliability in some areas, but it could nevertheless provide some good advice. Again, caution is needed and it would be sensible to refer to BS 7913: 2013 in order to reduce risks and take a more robust approach. PASSIVHAUS and ENERPHIT Passivhaus is defined as: ‘… a building for which thermal comfort can be achieved solely by post-heating or post-cooling of the fresh air mass, which is required to achieve sufficient indoor air quality conditions – without the need for additional recirculation of air’. A version has also been developed for retrofit and refurbishment called EnerPHit which Proposals are sometimes put forward for external wall insulation to be applied intermittently to the front elevation of individual houses in a terrace, despite there being features of architectural interest. A heritage impact assessment may prevent alterations like this from happening. Aesthetics are not the only consideration under the significance umbrella, but assessing significance will inevitably mean a greater likelihood of external wall insulation being applied to plain rendered elevations than to very ornate elevations with bay windows. This terrace is somewhere between the two, which is where the more difficult decisions lie. (Photo: Historic Environment Scotland) An EPC gives a property an energy efficiency rating from A (most efficient) to G (least efficient). Figures on the left give the SAP points required for each rating band.