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Frequently Asked Questions
SAP and RdSAP
SAP and RdSAP are both energy assessment methodologies for creating an Energy Performance Certificate (EPC), but they are used for different types of domestic properties: SAP (Standard Assessment Procedure) is for new builds, conversions, and extensions, while RdSAP (Reduced Data Standard Assessment Procedure) is used for existing, older properties. The key difference is that SAP involves detailed, invasive assessments, whereas RdSAP uses a simplified set of data combined with scientific assumptions for non-invasive surveys. There are different versions of SAP and RdSAP, the most recent versions are SAP10.2 and RdSAP10.
- Purpose: Used for new builds, conversions, and extensions to ensure compliance with Building Regulations, particularly Part L.
- Assessment: Requires a detailed, invasive assessment where all construction elements are measured and specified. It is produced at the design and as-built stages.
- Scope: Used for properties that are not yet built or have just been constructed.
- Purpose: Used for existing dwellings to produce an EPC. It was developed to be a quicker and less expensive method for assessing properties that are already built.
- Assessment: Is non-invasive. It relies on a streamlined set of data, with assessors using science-informed assumptions to fill in gaps where data is not directly observable, like opening up walls or floors.
- Scope: Used for existing residential buildings, including properties that were built before a certain date or those converted from a previous use.
A SAP score is a rating for ranking a dwelling's energy performance, calculated on a scale of 1 to 100+ which is complimented by a scale from A to G on an EPC. A higher score indicates a more energy-efficient home with lower running costs and lower carbon emissions. The score is calculated based on factors like the building's construction, heating and lighting systems, ventilation, and use of renewable technologies, but it does not account for cooking or appliance use which are based on a set occupancy calculation using the total floor area of the dwelling.
Part L
BRE develops and maintains the SAP and RdSAP methodology on behalf of the UK Government.
Part L of the building regulations focuses on conserving fuel and power by requiring higher energy efficiency standards for new and existing buildings, and it mandates a "fabric first" approach. Key requirements include higher levels of insulation, improved air tightness, stricter U-values for windows and doors, and more efficient heating, lighting, and ventilation systems. New builds must also meet a reduced carbon emissions target, and compliance requires a combination of design calculations (like SAP calculations) and "as built" verification through airtightness testing and photographic evidence. The approved documents can be located here: Conservation of fuel and power: Approved Document L - GOV.UK
MEES
Minimum Energy Efficiency Standards (MEES) are UK regulations requiring landlords to ensure their privately rented properties have an Energy Performance Certificate (EPC) rating of E or above, meaning properties with an F or G rating cannot be let. These standards, which also aim to increase the overall energy efficiency of private rentals to EPC Band C by 2030, came into force for existing tenancies in April 2020. Landlords may be subject to financial penalties for non-compliance and can apply for valid exemptions, such as the "7-year payback" exemption. Further guidance can be found here: Domestic private rented property: minimum energy efficiency standard - landlord guidance - GOV.UK.
Fuel Prices
For a SAP assessment, fuel costs are calculated using the fuel prices given in Table 12. The fuel prices given are averaged over the previous three years and across regions for SAP10 and the most recent prices are used for SAP2012. Other prices must not be used for calculation of SAP ratings. Since fuels must relate to realistic heating systems it is important that practical combinations of fuel types are used.
For an RdSAP assessment, Table 32 within the RdSAP10 specification replaces fuel prices in Table 12 of SAP10.2. As well as this, an additional set of prices which is updated more regularly is used when making improvement recommendations within an EPC and uploaded to the BRE SAP10 website.
SAP is a cost-based methodology, and the fuel prices influence many aspects of the calculation by determining the estimated energy costs, which form a major part of the final SAP rating. SAP calculations use government-approved fuel prices, and higher prices lead to higher estimated running costs, resulting in a lower SAP rating and an EPC that shows higher potential costs. The SAP assessment uses these costs for space heating, water heating, and lighting to calculate the dwelling's energy cost rating.
The SAP prices might not be reflective of today’s prices as the quantity is calculated based on historic prices. Due to the nature of obtaining fuel prices based on historic prices, the calculation will lag that of current day prices.
SAP2012 and SAP10 use different sets of fuel prices. SAP2012 uses the current cost while SAP10 uses a three-year average. This was facilitated to consider the cost/saving benefit associated with suggested improvement measures found on EPCs.
Fuel prices are updated bi yearly for SAP10 and quarterly for SAP2012. This may change aspects pertaining to the improvement measures of an EPC but not a SAP score which uses the fuel prices set within the RdSAP specification. This ensures that SAP assessments and scores are uniform despite fluctuating prices.
The fuel prices to be used for the calculation of EPCs account for incremental savings and total running costs. These prices are uploaded to Table 191 of the Product Characteristics Data File (pcdf2012.dat). The prices in Table 191 are used only for calculation of costs and savings on EPCs. Any SAP rating, whether initial, after incremental improvements or final, must in all cases be based on the prices given in Table 12 of the published specification of SAP 2012 or SAP10. Thus, software must maintain two sets of fuel prices, one set for calculation of SAP ratings and one set for calculation of running costs and savings.
This allows for a uniform assessment across dwellings independent of fuel price fluctuations for the SAP score while allowing for suggested improvement measures to be reflective of the actual cost/saving benefit.
Improvement measures
The EPC offers a section summarising of selected energy efficiency improvement measures. These are interventions relevant for the building that may improve upon its energy efficiency and energy rating and therefore reduce energy bills.
The savings that are quoted are the reductions in energy converted into costs based upon the relevant fuel prices. These prices (‘EPC costs’) are updated approximately every six months, and are intended to represent the typical cost of each fuel type. They are not the same prices used in the energy rating.
Energy efficiency measures make several assumptions as to suitability of the building for improvement. These are given in detail in Appendix T of the RdSAP 10 specification. However, only a detailed survey can establish for sure whether the measure can be applied. The energy assessor will remove any improvement measures that are clearly not possible at the time of assessment.
The improvements are theoretical in the same way as the energy assessment – they assume the building is occupied and operated in a standard way. Occupants may get different results in reality.
The indicative capital costs for each measure are also presented in the EPC. These are based on DESNZs best estimates for cost of measures and may include the indirect costs of installation – they are not the material costs but are likely to include labour and any other preparation work required. Capital costs can be very complex and bespoke to a project, so the capital costs are presented as indicative information only.
The building owner should take advice from a qualified installer before applying any of the suggested energy efficiency measures.
Domestic Energy Assessors (DEAs) Queries
BRE develops SAP and RdSAP on behalf of government. There is a process in which an assessor should contact their accreditation scheme first to obtain advice about whatever situation may occur. This can range from a peculiarity within a dwelling where some building elements cannot be determined or categorised, to a calculation error. The scheme will then judge whether they raise the query with BRE.
RdSAP2012 Vs RdSAP10
A detailed list of the changes in RdSAP 10 can be found in the RdSAP specification introduction section (page 6). Briefly, some of the main differences are:
- Measurements required for all windows
- Mechanical ventilation is treated as in full SAP allowing for PCDB entry
- PV is calculated as in SAP10.2 - PV Diverter and Batteries have been added
- Air pressure test result can be used if available
- All tables of U-values updated
The latest version of RdSAP has been updated to consider the dwelling in more detail. In some cases, instead of assuming default values, the assessor must enter the precise values relevant to that dwelling. This may reduce the EPC score in some cases or improve it in others. This change is applied equally to all dwellings assessed using a new methodology and is an integral part of updating and improving energy rating methodologies.
There are two variants of fuel costs used in the SAP methodology:
- Fixed costs (‘Table 12’) which are only updated for every methodology update, and
- EPC costs, which are updated every six months. The SAP rating is calculated using ‘fixed costs’.
This is because the SAP rating needs to be calculated using consistent costs between dwellings, so that they can be compared more easily. Fixed costs may not correspond well with current costs in the real world; they are present to reflect the differences between the cost of fuel types. In addition, SAP calculations are subject to a ‘cost deflator’ calculation that
The costs you see on an EPC are calculated using EPC costs, to ensure that you see the most up to date.
BREs role
BRE does not own SAP or RdSAP. BRE develops and maintains SAP and RdSAP methodology on behalf of the UK Government.
BRE approves third party SAP and RdSAP software on behalf of the UK Government. Third party software is tested against BREs reference engine. BRE does not have a marketable version of SAP or RdSAP software.
Energy Assessors use Approved SAP and RdSAP software to conduct energy assessments.
Approved SAP and RdSAP software can be found on the BRE website.
Approved software and Schemes role
BRE develops and maintains the SAP and RdSAP methodology on behalf of the UK Government, however, BRE does not carry out energy assessments. Energy assessments are carried out by third party assessors, using software which has been tested against BRE’s reference engine and approved by BRE.
BRE is not a DEA scheme. Energy assessors can be found here: Get a new energy certificate - GOV.UK