33 CATHEDRAL COMMUNICATIONS THE BUILDING CONSERVATION DIRECTORY 2025 PROFESSIONAL SERVICES 1 is a cost-based metric, using electricity directly to generate heat will lead to a building scoring poorly compared with a gas-powered alternative. Often historic buildings have electric panel heaters rather than central heating systems and the price per unit of electricity is leading them to score poorly. RdSAP then considers how this fuel is converted into space heat by considering how effective the building systems are at doing this. This is where RdSAP is reliant on the Product Characteristics Database (PCDB). This contains performance information for boilers, heat pumps, mechanical ventilation systems and so on. This information tells RdSAP how much energy in the fuel is effectively converted into heat. For information to be published in this database, manufacturers must have products independently tested and then pay a fee for their product to be added to the database. The database is publicly available online so the performance figures can be seen for each system6. When an assessor inspects a building, they will look up the boiler in the PCDB; if it isn’t there, they must assign a default performance value for that type of heating technology. This performance value can be significantly lower than reality. The older the technology, the less likely it is to be in this database. Also, as the database is dependent on manufacturers paying to submit their information to it, there are several heating systems that aren’t included. It is important to note that the PCDB is different to the Microgeneration Certification Scheme (MCS) commonly used for renewable heat technology incentives such as the government’s boiler upgrade scheme. Be aware that a products inclusion on the MCS does not guarantee inclusion on the PCDB. The space heating systems that achieve the best ratings are generally central heating systems powered by modern condensing gas boilers or high efficiency heat pumps. Both of these should have time programmers, thermostats, TRV’s and weather compensators. For gas, this converts a cheap energy source effectively into heat and with a heat pump it overcomes the cost deficit to gas with efficiencies of 350 per cent and more. For RdSAP the next biggest cost after space heating is the generation of hot water. In an older building hot water is typically stored in a cylinder with a thin layer of insulation. This presents an opportunity for heat loss, so simply adding a thicker cylinder jacket will give a slightly higher EPC score. Using electricity to heat water via an immersion heater is expensive due to the price of electricity. As with space heating, the best ratings will be achieved by using an efficient gas boiler or a latest generation heat pump combined with a modern hot water cylinder with a thick foam jacket. This will mean the hot water is generated and stored for the least cost. HOW TO UPGRADE THE EPC RATING Historic buildings are very capable of achieving good EPC ratings. We must be careful and take a risk-based approach when retrofitting, with interventions being tailored to the age, construction and use of the building. The heritage value and significance must also be considered at every stage of a retrofit project. How this EPC rating could be improved Space heating The primary space heating could be upgraded to a well-controlled, low temperature central heating system powered by the latest generation air source heat pump that also heats a modern insulated hot water cylinder. A sealed log burner could also be installed within the fireplace. This lifts the rating to a D due to the heat pump’s high efficiency. Insulation To further improve on the D-rating, the next step could be adding 300 mm of sheep’s wool insulation between the joists in the well-ventilated roof space. There may also be an opportunity to upgrade single-glazed windows with either slimline, double-glazed units or secondary glazing. The lighting could also be upgraded to LED. These measures could lift this property to a C. Energy generation Building on this again, the property has a large area of south facing roof and so 40 per cent of the roof area could have solar panels added to it. This lifts the rating into the B band through reduction in energy supply cost. High risk areas (such as walls and floors) 50 mm insulated lime render could be added to the external sandstone walls, potentially lifting the rating to an A. While not all these measures will be appropriate for all buildings (and not all relevant permissions may be achievable), this example illustrates that it is possible to get a very good EPC rating for a historic property by first looking at systems and efficiency before pushing forwards with fabric changes. The biggest rating improvements in the historic environment will likely come from taking advantage of the latest high efficiency heat pump technologies and using on-site energy generation systems (solar panels or wind turbines). There is an everincreasing knowledge base surrounding retrofit in the historic environment and it has become clear that our heritage assets are capable of using much less energy and producing significantly fewer emissions. While their historical significance is undeniable, historic buildings also hold a key to achieving our climate goals. By embracing sensitive upgrades and rejecting one-size-fits-all solutions, we can ensure these treasured structures contribute to a greener tomorrow. References 1 www.gov.uk/find-energy-certificate 2 Energy Performance of Buildings Certificates Statistical Release: July to September 2024 England and Wales, Ministry of Housing, Communities & Local Government, bc-url.com/ BCD25_11 3 www.bregroup.com/expertise/energy/sap 4 www.gov.uk/government/statistics/ council-tax-stock-of-properties-2024 5 U-Value Report, SPAB, 2012, bc-url.com/ BCD25_13 6 www.ncm-pcdb.org.uk/sap/index.jsp SIMON LOCK MEng is Sustainability Director, Woohoo Ltd (woohoo.ltd) a consultancy specialising in heritage and sustainability. TYPE Two-storey detached Victorian building with no extensions FLOOR AREA 200 sq m floor area with no extensions FLOOR BUILD UP Solid floor WALLS 500 mm thick sandstone walls WINDOWS Single-glazed timber sliding sash windows CEILING / ROOF No insulation to ceiling (accessible loft) LIGHTING No energy efficient lighting SPACE HEATING Electric space heaters and open fireplace HOT WATER Immersion heater. Thinly insulated cylinder with an immersion heater EPC RATING G (largely due to its high dependence on electricity for heating) Example site
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