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What Is SAP? — Standard Assessment Procedure
A plain-English guide to SAP: the UK government's method for assessing the energy performance of dwellings, Part L compliance, and EPC ratings.
Definition
SAP (Standard Assessment Procedure)is the UK government's methodology for assessing and comparing the energy performance of dwellings. Developed by the BRE (Building Research Establishment) on behalf of BEIS (now DESNZ), SAP provides the calculation framework used to demonstrate compliance with Part L of the Building Regulations and to generate Energy Performance Certificates (EPCs) for all UK homes.
When Is It Used?
SAP is used at two key stages of every new dwelling: at design stage to demonstrate that the proposed design meets Part L targets, and at completion (as-built stage) to confirm compliance and generate the EPC. RdSAP (the reduced-data version) is used whenever an EPC is needed for an existing home being sold, rented, or assessed for grant eligibility. SAP results also feed into the Target Emission Rate (TER) and Target Primary Energy Rate (TPER) calculations that determine Part L compliance.
Key Facts
- Current version: SAP 10.2 (in use since June 2022 with Part L 2021)
- SAP score range: 1 to 100+ (higher = more energy efficient, lower running costs)
- Two compliance metrics: Target Emission Rate (TER) and Target Primary Energy Rate (TPER)
- SAP 10.2 uses updated electricity carbon factors, favouring heat pumps and electric heating
- The PCDB (Product Characteristics Database) provides boiler and heat pump efficiency data
- Thermal bridging: default y-value (0.15), ACDs (0.08), or calculated psi-values can be used
- Airtightness test results feed directly into the as-built SAP calculation
- The Home Energy Model (HEM) will eventually replace SAP as the primary assessment method
Related Calculators
Use the U-Value Calculator for fabric inputs to SAP, or the EPC Rating Estimator for approximate ratings. See also the EPC glossary entry, Thermal Bridge glossary entry, and the Part L U-Values reference table.
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How We Calculate This
Frequently Asked Questions
SAP (Standard Assessment Procedure) uses detailed design data and is required for new-build dwellings. It uses exact insulation thicknesses, boiler efficiency data from the PCDB, calculated thermal bridging values, and designed ventilation rates. RdSAP (Reduced Data SAP) is a simplified version used for existing dwellings. It uses data collected during a site survey and fills gaps with assumptions based on building age and type. RdSAP is used to produce EPCs for existing homes.
A full SAP calculation is required for all new dwellings and conversions creating new dwellings to demonstrate Part L compliance. Two SAP calculations are needed: a "design stage" SAP (submitted with the Building Regulations application) and an "as-built" SAP (after construction, reflecting any changes). The as-built SAP generates the new-build EPC. SAP is also required for extensions over 25% of the existing floor area in some circumstances.
SAP produces a score from 1 to 100+ (higher is better), based on the annual energy cost per m² of floor area. A rating of 100 represents zero net energy cost. Ratings above 100 are possible for dwellings that are net energy exporters. The SAP score maps to the EPC rating bands: A (92+), B (81-91), C (69-80), D (55-68), E (39-54), F (21-38), G (1-20). Part L 2021 requires the dwelling to meet a Target Emission Rate (TER) and Target Primary Energy Rate (TPER).
SAP 10.2 is the current version, used since June 2022 for Part L 2021 compliance. Key changes from SAP 2012 include updated carbon emission factors (electricity is now lower-carbon due to grid decarbonisation), updated fuel prices, improved treatment of heat pumps and solar PV, and the addition of a primary energy metric alongside carbon emissions. The Home Energy Model (HEM) is being developed as the eventual replacement for SAP.
SAP calculations must be carried out by an accredited SAP assessor using approved software (e.g., Elmhurst SAP, Stroma FSAP, JPA Designer). SAP assessors are accredited through schemes such as Elmhurst Energy, Stroma, ECMK, or Quidos. A SAP calculation for a typical new-build house costs £150-£350 at design stage and a similar amount for the as-built assessment. Most SAP assessors also produce the new-build EPC as part of the service.
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Last updated: March 2026
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