How are EPCs produced?

[edit] Background to EPC's

Energy performance certificates (EPCs) are required when buildings are built, sold or rented, via a brief assessment they allocate a building energy efficiency rating from the most efficient (A) to the least efficient (G). The certificate also highlights energy efficiency improvements that could be made to improve the rating, with indicative costs verses benefits.

The concept of the energy performance certificate (EPC) stemmed from a European Union Directive entitled the Energy Performance of Buildings Directive (EPBD) which was introduced to the UK in 2003. The intention was to find some way of rating buildings on the same basis to create indicative bar ratings, in the same way as energy labels had done.

Energy labels had been introduced in the 1990's to increase awareness of how efficient individual appliances were. The programme was considered a successful in that it drove innovation and slowly changed the market of for example white goods resulting in only better performing product being available. Products improvements were significant enough that in 2011 new gradings of efficiency had to be introduced in A+, A++ and A+++, today very few products at the lower ends of the scale are sold.

[edit] EPCs for non-domestic buildings

The basis of the EPC for non domestic buildings uses a mathematical model called the Simplified Building Energy Model (SBEM), which is one Government approved methodology and is a requirement for any new build, refurbished or extended commercial building larger than 50m2. The SBEM calculations consider building fabric, heating, hot water, cooling, ventilation and lighting and produce a resulting Building Regulations UK Part L (BRUKL) as evidence that a building complies with the Building Regulation requirements.

Other modelling tools are also available and often used, they can normally also produce a BRUKL report as one output, the SBEM and approved tools can usually also take into consideration an renewable technology employed on the building. The report looks at the overall energy performance and carbon emissions in terms of a Target Emission Rate (TER), which is an 'as designed' model that meets the regulations, and in terms of Building Emission Rate (BER), the assumed figure for the building in question or as built rate. If the BER given in the report is lower than the TER then the building is said to comply with the Building regulations Part L2, if it is higher then it does not comply and needs to be improved until it does. The EPC can then be produced based on the Building Emission Rate.

For larger public buildings as described a Display Energy Certificate (DEC) is required this is a different methodology from an SBEM and EPC because gives an indication of the energy performance of a building based on actual energy consumption, as opposed to modelled energy consumptions, comparing it to a modelled building of a similar use and type.

The SBEM tool has been updated and improved at regular intervals since it was launched, the most current version being SBEM non-domestic version 6.1b which was updated in June 2022. These changes to the modelling tool incorporated allowances to support the changes in the building regulations as well as adjustments to the carbon factors of different energy sources. That means the average accepted carbon emissions that are associated with using a particular fuel. For electricity, because of the increased contribution of renewable energy sources contributing to the grid the associated emissions per KWh has reduced, whilst at the same time has remained the same or increased in terms of associated emissions.

Other building assessment methods exist for non-residential buildings that are based on actual energy used, these are referred to as Display Energy Certificates (DECs) and although they look similar they are not the same. Since January 2013 DEC's have been required in buildings over 500m2 that are occupied by public authorities or institutions providing a public service, they also need to be displayed near the entrance of the building. Other optional assessment methods that look in more detail at the performance of buildings are referred to as Post Occupancy Evaluations (POEs) or Building Performance Evaluations (BPEs).

[edit] EPC's for domestic buildings

There are in fact two versions of the same modelling tool that are used to calculate the energy performance of domestic buildings and in turn produces domestic EPC's. in the same way that SBEM has been updated at regular intervals since its launch, so to has the Standard Assessment Procedure (SAP) for dwellings. The current SAP is version 10.2 which was introduced in 2022 and is for use on new dwellings. The elements that were adjusted included; shower flow rates, lighting efficacies, heating networks, chimneys and flues, MVHR, flow temperature for heat pumps and condensing boilers, hybrid systems, PVs, battery storage and diverters, solar thermal for space heating, heating patterns, controllers and building characteristics as well as prices, similarly to SBEM the emissions and primary energy factors.

The second version of SAP which is often used for existing buildings and refurbishments is called the Reduced Data Standard Assessment Procedure (RdSAP) the current version of RdSAP v9.94 was launched in 2012 but an updated version of the model is expected to be released in 2024, most likely with similar updates as were made to in SAP10.2.

The Government document "Energy Company Obligation SAP and RdSAP Amendments" was published in September 2023

[edit] Related articles on Designing Buildings

• Accredited energy assessor.
• Air tightness.
• Are Energy Performance Certificates accurate?
• BS EN 15232 Energy performance of buildings: impact of building automation, controls and building management.
• Building performance.
• Building Performance Evaluation.
• Building performance metrics.
• Building Regulations UK Part L (BRUKL)
• Carbon ratings for buildings.
• Certificates in the construction industry.
• Display energy certificate.
• Emission rates.
• Energy certificates for buildings.
• Energy efficiency of traditional buildings.
• Energy Performance of Buildings Directive.
• Energy related products regulations.
• Energy Savings Opportunity Scheme.
• Energy targets.
• Green mortgage.
• Home information pack HIP.
• Homebuyer Report.
• How much does it cost to sell my home.
• Listed buildings.
• Minimum energy efficiency standard (MEES).
• Minimum energy efficiency standard regulations for domestic and non-domestic buildings.
• NABERS UK.
• National Calculation Method.
• National Retrofit Strategy NRS.
• Non-domestic private rented property minimum standard.
• Passivhaus vs SAP.
• Performance gap.
• Post Occupancy Evaluations.
• Private rented sector regulations and traditional buildings.
• Retrofit.
• Simplified Building Energy Model.