How much is a SAP Calculation?

Our fees are typically based upon the size and complexity of a dwelling. We prefer to offer a bespoke quotation on a job-by-job basis to give you the best price – get in contact and send us your plans today!

Can I do a SAP Calculation for conversions myself?

SAP Calculations must be carried out by an On Construction Domestic Energy Assessor (OCDEA), working with approved Government software. The Assessor must be certified under one of several accreditation schemes and is regularly audited to keep their certification.

What is required for a SAP Assessment?

Your Assessor will advise you of exactly what is needed. Typically you would need: floor plans, sections & elevations; site orientation; construction specification of walls, roofs and floors; specification for all windows; primary & secondary heating systems; renewable technology (if any).

Are SAP Calculations the same as an Energy Performance Certificate?

No, SAP Calculations and Energy Performance Certificates (EPCs) are not the same. SAP Calculations determine a building's energy performance and are used for Building Regulations compliance. An EPC shows the energy efficiency rating from A to G and provides recommendations for improvement. The EPC uses the results of the SAP calculation.

What Are SAP Calculations? – Complete Guide

Q: What are SAP Calculations?

SAP stands for ‘Standard Assessment Procedure’ and is the government’s method for calculating the energy performance of dwellings. These calculations are only necessary for residential properties. The calculations determine a Target Emissions Rate (TER) and a Target Fabric Energy Efficiency (TFEE) rate. Also find out: How do extension SAP calculations differ from new builds or conversions?

Q: What happens if my design fails its SAP Assessment?

If your design fails its SAP Assessment, you will need to revise the design to meet the requirements. Depending on the changes required, you may need to go through the assessment process again. In some cases, additional testing may be needed. The SAP Assessor will provide guidance on the necessary steps to make your design compliant.

Introduction

If you are planning a new build, a conversion, or even a large extension in the UK, you may have already heard about SAP calculations. But what exactly are they, why are they required, and how can you make sure your project passes?
This guide will walk you through everything you need to know about SAP (Standard Assessment Procedure) calculations — from the basics, through examples, to practical tips for compliance.

What Does SAP Stand For?

SAP stands for Standard Assessment Procedure. It is the UK Government’s approved method for assessing the energy performance of dwellings. The system has been in place since 1995 and is continually updated to align with Building Regulations and environmental targets.

In short, SAP measures how energy-efficient your property will be, and whether it meets the requirements of Part L of the Building Regulations.

Why Are SAP Calculations Required?

Under Part L of the Building Regulations, SAP calculations are mandatory for:

All new dwellings (houses, flats, apartments).
Conversions (e.g. office-to-residential, barn conversions).
Extensions where more than 25% of the existing thermal envelope is changed.

The main purposes are:

To demonstrate compliance with energy and carbon targets.
To produce an Energy Performance Certificate (EPC).
To ensure the property is future-proof in terms of running costs and sustainability.

What Do SAP Calculations Involve?

During a SAP assessment, several elements of the property are analysed:

Building fabric (walls, floors, roof, insulation).
Windows and doors (type, size, U-values).
Heating systems (boilers, heat pumps, radiators).
Hot water and ventilation systems.
Renewables (solar PV, battery storage, etc.).

The calculations compare:

DER (Dwelling Emission Rate) with TER (Target Emission Rate).
DFEE (Dwelling Fabric Energy Efficiency) with TFEE (Target Fabric Energy Efficiency).

To pass, the dwelling’s DER and DFEE must be lower than or equal to the target values.

How Are SAP Calculations Carried Out?

Design Stage SAP
- Done before construction.
- Requires drawings, specifications, insulation values, heating details.
- Produces a predicted EPC and ensures design compliance.
As-Built SAP
- Completed once the property is built.
- Must match the final construction details.
- Results in the official EPC lodged with the government database.

Both stages must be completed by an OCDEA (On Construction Domestic Energy Assessor) using government-approved software.

Example SAP Calculation

Let’s look at a simplified example:

A new 100 m² house with cavity wall insulation, double glazing, and a gas boiler.
DER (Dwelling Emission Rate) = 17 kgCO₂/m² per year.
TER (Target Emission Rate) = 18 kgCO₂/m² per year.

Result: Pass (17 is lower than 18).

Now, if the same house had poor insulation and single glazing:

DER = 21 kgCO₂/m² per year.
TER = 18 kgCO₂/m² per year.

Result: Fail. Improvements would be needed (e.g. better insulation or renewable technologies).

Typical Costs and Timescales

Prices for SAP calculations typically start from £75–£120 per dwelling (depending on complexity).
Larger projects, conversions, or urgent turnarounds may cost more.
Turnaround times can be as quick as 24–48 hours for standard jobs.

Common Mistakes and How to Avoid Them

Insufficient insulation values — not matching design assumptions.
Incorrect heating system specs — boiler efficiency overstated.
Missing ventilation details — leading to default (unfavourable) assumptions.
Leaving SAP too late — design changes become costly if discovered post-build.

Tip: Always commission a design-stage SAP early, ideally before building control approval.

SAP for New Builds vs Conversions vs Extensions

How to Pass Your SAP Calculation

Upgrade insulation levels where possible.
Opt for efficient glazing (low U-values).
Consider renewable options (solar PV, heat pumps).
Choose efficient heating and hot water systems.
Reduce air leakage by ensuring good airtightness

Conclusion

SAP calculations are a crucial part of the building process in the UK, ensuring homes are energy efficient and compliant with Part L of the Building Regulations.

By understanding what SAP calculations involve, when they are required, and how to prepare, you can save time, money, and avoid costly redesigns.

👉 Need a SAP calculation for your project?
Contact us today for a fast, accurate, and affordable service.

Frequently asked questions

General

If your design fails its SAP Assessment, then you will need to revise the design to meet the requirements. Depending on the extent of the changes required, you may need to go through the assessment process again. In some cases, you may need to have additional testing done to verify the design’s performance. The SAP Assessor will provide guidance on the necessary steps to make your design meet the requirements.

No, SAP Calculations and Energy Performance Certificates (EPCs) are not the same. SAP Calculations are used to determine the energy performance of a building and are used in the UK to comply with Building Regulations. An Energy Performance Certificate is a certificate that shows the energy efficiency of a building and is required when a building is built, sold, or leased. The EPC uses the results of the SAP calculation to give the building a rating from A to G, with A being the most energy efficient and G being the least. The EPC also provides recommendations for improving the energy efficiency of the building.

SAP Calculations for all your building projects

Embarking on a New Build or Conversion journey? Explore a range of specialized services tailored to your project's needs. Our experts offer a suite of offerings, from Energy Statements, "Part O" Reports, PSI & U-Value Calculations, and more.

Let's elevate your project together. Reach out today to discover the possibilities.

UK Building Compliance Price List

Service Typical Cost (no VAT added)

Details

SAP Calculation (New Build / Conversions/Extensions - including Highly Glazed) From £99 – £295 per dwelling

U-value Calculation (Standalone) £25 – £50 per element Individual wall, floor, or roof — EN ISO 694

U-value Bundle (3–5 elements) £80 – £120 Covers most of a standard build envelope

Custom U-value + Condensation Risk £100 – £180 Adds interstitial condensation (Glaser method, EN ISO 13788)

Energy Statement (Planning Stage) £150 – £395 For council carbon & energy policy (e.g. London Plan)

Part O Overheating – Simplified Method £150 – £200 Only valid when glazing ≤25% and ventilation criteria are met

Part O TM59 – Dynamic Modelling £800 – £1,500 + Required when glazing >25% or simplified method fails

Extra SAP modelling for high-glazing compensation £100 – £250 Additional design iterations, shading, PV, upgraded glazing, or MVHR

SAP + Part O + U-values Bundle (≤25% glazing) £250 – £600 per unit Most common bundled rate (when no TM59 needed)

SAP + TM59 + U-values (high-glazing bundle) £900 – £1,600 per unit For highly glazed dwellings requiring full thermal modelling

Part L1A

SAP Calculations for New Builds

Nowadays, every new dwelling must undergo a SAP calculation during the design stage to show compliance with Part L1A of the Building Regulations.

Part L1B

SAP Calculations for Extensions

When constructing an extension with glazing covering over 25% of the floor area, we can conduct SAP Calculations to validate compliance with Part L1B Building Regulations.