EPC changes for existing buildings

1 Background
2 Past criticism, future considerations
3 Updated methodology
4 What does this mean for owners, landlords and tenants?
5 Related articles on Designing Buildings

[edit] Background

Energy Performance Certificates (EPCs) rate the energy efficiency of both new and existing buildings and suggest improvements that could be made. Originally introduced in 2003 via an EU directive, EPCs aimed to standardise efficiency ratings, inspired by successful appliance energy labels that drove market innovation and led to stricter efficiency grading systems.

EPCs set out the energy efficiency rating of a building from A (most efficient) to G (least efficient) and are valid for 10 years. The EPC contains information about a property’s energy use, typical energy costs and recommendations about how to reduce energy use and save money. The calculation methodology behind residential EPCs is known as the Standard Assessment Procedure (SAP), with a slight variation known as the Reduced Standard Assessment Procedure (RdSAP), which is used for existing residential buildings.

For buildings other than dwellings, the National Calculation Method (NCM) is used, which is based on the Simplified Building Energy Model (SBEM), the equivalent of SAP but with a number of differences. Both SAP and SBEM are energy estimating tools rather than actual energy measurement tools. In the case of some public buildings there is also a requirement to use and display a measured energy rating tool based on a yearly assessment; this is called the Display Energy Certificate (DEC).

[edit] Past criticism, future considerations

Because the methodology behind an EPC is a simplified estimate it has for some time faced criticisms regarding common inaccuracies, which have become more vocal as requirements have become more stringent. Studies have highlighted flaws such as mismeasured floor areas, poor fabric assumptions, occupant usage and so on, often leading to overestimations of energy use. Inaccuracies in the procedure itself can stem from these assumptions, outdated or simplified modelling software, incorrect data points, human error, behaviour-based variability, weather conditions, building changes over time, default U-values and so on.

The requirements to hold an EPC have gradually changed over time. Initially, from 2008, EPCs became mandatory for all buildings being sold, built, or rented, and then from 2018, with the introduction of the minimum energy efficiency standard (MEES), a minimum EPC rating of 'E' was required for new tenancies. In 2020 this was then expanded to all existing tenancies, in effect meaning that from April 2023, landlord properties with ratings below 'E' could not legally be let. Whilst the new requirements covered much of the rental stock, a variety of exemptions were given for short-term lets, historic buildings, and so on.

In February 2024 the Building Research Establishment (BRE) published a specification for its RdSAP, whilst the government published a number of consultations regarding MEES and EPCs, reviewing both the methodologies and the requirements for these.

The current government proposal is to raise the minimum EPC rating to 'C' for new tenancies by 2025 and then for all tenancies by 2028, and alongside this, change the process by which exemptions apply. Whereas currently certain properties default to having an exemption, the new regime will have the default of applying to all properties, including short-term lets and historic buildings. Whilst certain exemptions will continue to exist, they will need to be applied for, evidenced and recorded on a register, with aspects such as the amount of money spent on energy efficiency improvements being considered.

[edit] Updated methodology

The methodology to calculate the EPC rating level of new buildings has been updated at various points, with the latest version of SAP, SAP 10.2, including many more data points than were originally considered. The methodology used to calculate the EPC of existing buildings, RdSAP, although updated regularly, has largely remained the same, RdSAP v9.94. However, in February 2024, BRE published the specification for the new updated RdSAP10, promising to be a much more detailed calculation of energy performance, helping to produce significantly more accurate EPCs for existing buildings. The specification brings the SAP approach for existing dwellings much closer to the approach that is used for new buildings.

The new RdSAP specification has been developed by BRE on behalf of the government for use in existing dwellings based on a site assessment of the property when the complete dataset for SAP calculation is not available. The RdSAP calculation, starting from reduced data, is done in two stages. First the collected data (reduced data set) is expanded into a full data set, and then the SAP calculation is undertaken using the expanded data set. The SAP calculation is therefore identical, whether starting from a reduced data set or a full data set. This version of RdSAP forms part of the SAP 10.2 specification and provides a data input set for use with version 10.2 of SAP.

BRE state that there are significant changes in RdSAP 10 when compared to the RdSAP 2012 specification, and these include:

Window measurements required for all windows
Location of each window allocated to main walls or each extension, or alternative walls
Thermal properties of insulation revised
Roof insulation details have more options.
Floor insulation revised; heated basement details added
Table of Window U-Values expanded
U-values of brick walls revised to account for wall thickness
U-values of stone walls revised
Curtain wall added as a new wall type
Window shutters added as a new feature
Hot water tank size included
Hot water tank insulation included
Room in roof (RR) revised to take into account all elements, including the continuous main wall.
Additional alternative/shelter wall added
Mechanical ventilation is treated as in full SAP, allowing PCDB entry and still allowing default values.
PV calculated as in SAP10.2
PV Diverter for water heating added
PV batteries added
Ventilation algorithm allows more options
Air pressure test results can be used if available.
New age-band M added, and all tables of U-values updated
Data for the Isle of Man added for completeness of information
Table 32 with the RdSAP10-specific fuel prices replaces fuel prices in Table 12 of SAP10.2.
RdSAP10-specific metrics added to replace SAP metrics in SAP10.2
Small-scale hydro added as in SAP10.2
Flue gas heat recovery – calculation according to SAP 10.2.
Wastewater heat recovery – calculation according to SAP 10.2.
Heat pumps – Calculation according to SAP 10.2.
Changes to Table 21 of improvement measures (former RdSAP Appendix T) include:
- Improved U-values revised for all building elements
- Measure to insulate party wall removed
- Order of measures for Northern Ireland removed
- Air and ground source heat pumps are not alternative measures any more.
- PV battery and PV diverters added

[edit] What does this mean for owners, landlords and tenants?

Firstly, because of the higher level of detail captured by the new RdSAP model, assessors will most likely take longer to assess a property, input the data and create the certificate. This means it is most likely that the cost of generating an EPC will go up; currently costs can vary from around 60 to 120 pounds. This does, however, mean that for tenants in particular, the newer EPCs should be a truer reflection of the energy performance of a property.

Secondly, because the new model captures a greater level of detail, it is likely that owners and landlords may be required to evidence any upgrades that have been made for them to be incorporated into the EPC rating, rather than using default values. For example, the performance of newer double-glazed windows versus older models or the installation of insulation that is not easily seen by an assessor.

It is worth noting however, that under the current Minimum Energy Efficiency Standards (MEES), a spending of up to £3,500 (including VAT) might be expected on energy efficiency improvements to a property that is let in order to bring it above an EPC level E. In the future this level will increase to C and will also apply to short lets and historic buildings with the same spending cap, so it is worthwhile keeping a record of any energy efficiency improvements that are made and the costs.

If a landlord feels that they might be exempt from meeting a certain standard because they have spent up to the cap and not met the newer standard, again, this may have to be evidenced in order to apply for an exemption. Furthermore, the landlord will be required to register an exemption on the government website here.

To find out more about possible sources of third-party funding to help meet the minimum energy efficiency standards, visit the government energy-efficient home campaign website here.

--editor