SAP calculations assess the predicted energy performance of residential buildings. They are used to demonstrate compliance with Part L of the Building Regulations and help produce Energy Performance Certificates for new homes.
The assessment considers the construction of the dwelling, its heating and hot water systems, ventilation, lighting, airtightness and any renewable technologies. It allows the energy performance of a proposed dwelling to be reviewed before construction and confirmed once the building is complete.
SAP calculations are an important part of the design and Building Control process for new homes, residential conversions and certain extensions.
What Does SAP Stand For?
SAP stands for Standard Assessment Procedure.
It is the methodology approved by the UK government for calculating and comparing the energy performance of dwellings. SAP uses standard assumptions about occupancy and how a home is used. This allows different properties to be compared on a consistent basis.
The calculation estimates the energy required for space heating, hot water, ventilation and lighting. It also considers the amount of energy generated by technologies such as solar photovoltaic panels.
The results are used for two main purposes. The first is to demonstrate compliance with the relevant energy requirements of the Building Regulations. The second is to produce an Energy Performance Certificate, commonly known as an EPC.
SAP is used for residential buildings. Non residential buildings are normally assessed using a different methodology called the Simplified Building Energy Model, or SBEM.
When Are SAP Calculations Required?
SAP calculations are normally required when a new dwelling is created. This includes individual houses, blocks of flats and larger residential developments.
They may also be required when an existing building is converted into residential accommodation. Examples include an office converted into flats, a barn converted into a home or an existing house divided into separate dwellings.
Some extensions also require a SAP calculation. This is particularly relevant where a proposal does not follow the standard elemental approach contained within the Building Regulations. A common example is an extension containing more glazing than would normally be permitted.
A SAP calculation can sometimes demonstrate that improvements elsewhere compensate for the additional heat loss through the glazing.
The exact requirement depends on the type of project, its location and the regulations applying to it. Building Regulations differ between England, Wales, Scotland and Northern Ireland, so the correct approach should be confirmed for each project.
How Do SAP Calculations Work?
SAP calculations are normally completed as a desktop assessment. The assessor uses architectural drawings and technical specifications to create an energy model of the proposed dwelling.
The model includes the dimensions and orientation of the building, the areas of walls, floors, roofs, windows and doors, and the thermal performance of each element.
The assessor also enters details of the heating, hot water, ventilation and lighting systems. Thermal bridging, air permeability and renewable technologies are included where relevant.
The software uses this information to calculate the dwelling’s predicted energy performance. The proposed dwelling is then compared with the applicable targets and minimum standards.
If the initial design does not comply, the assessor can investigate which parts of the specification are causing the problem. Different improvements can then be tested before the design is finalised.
This is one reason SAP calculations should be treated as a design tool rather than a final administrative exercise.
What Information Is Used in a SAP Calculation?
The assessor will normally begin with the architectural floor plans, elevations, sections and site plan.
The site plan is important because it establishes the orientation of the dwelling. Orientation affects the amount of solar energy entering through the windows and can therefore influence the calculation.
Detailed construction build ups are required for the walls, floors and roofs. These are used to calculate or confirm the relevant U values.
The assessor will also require information about windows, rooflights and external doors. This can include their dimensions, U values, frame details and solar transmittance.
Heating and hot water information is also needed. The calculation considers the type of system, its efficiency, controls, distribution and storage losses.
The ventilation strategy, lighting, thermal bridge details, proposed air permeability and renewable technologies must also be included.
The accuracy of the calculation depends on the quality of the information provided. Where information is missing, the assessor may need to use assumptions or conservative default values.
What Does a SAP Calculation Assess?
A SAP assessment considers the dwelling as a complete energy system. Improving one part of the design may influence several different results.
The building fabric is an important part of the assessment. Heat loss through the external walls, floors, roofs, windows and doors is calculated using their areas and thermal performance.
Thermal bridging is also included. This considers additional heat loss through junctions such as wall and floor connections, roof edges and window openings.
Air leakage affects the amount of heat lost through uncontrolled ventilation. A design air permeability figure is used during the early assessment. The measured air test result is then used when the dwelling is complete.
Heating and hot water systems can have a significant effect on carbon emissions and primary energy use. The assessment considers the type of equipment, efficiency, controls and associated losses.
The calculation also includes ventilation, lighting and renewable technologies such as solar photovoltaic panels.
These elements must be coordinated. A specification that performs well in one area may still struggle if another part of the design is weak.
What Do the SAP Results Mean?
The SAP assessment produces several results rather than one simple pass or fail score.
The SAP rating is a measure of the dwelling’s calculated energy cost under standard assumptions. A higher rating generally indicates better energy performance and lower calculated energy costs.
For Building Regulations compliance, the assessment also considers applicable performance targets. These can include the dwelling’s calculated carbon emission rate, primary energy rate and fabric energy efficiency rate.
The proposed dwelling is compared with corresponding targets based on a notional dwelling. Relevant minimum standards for individual construction elements and building services must also be satisfied.
The precise compliance outputs depend on the methodology and regulations applying to the project. Your assessor should explain which results are relevant and what they mean for the design.
What Is the Difference Between SAP Calculations and an EPC?
SAP calculations and EPCs are closely connected, but they are not the same thing.
The SAP calculation is the detailed assessment used to determine the predicted energy performance of the dwelling and demonstrate Building Regulations compliance.
The EPC is the certificate that presents the property’s energy rating in a standard format. It places the dwelling within an energy efficiency band and provides information about its calculated energy performance.
For a new dwelling, the design stage SAP calculation is completed before construction. Once the building is finished, the assessment is updated to reflect the completed specification. The final assessment is then used to produce and lodge the EPC.
What Is the Difference Between Design Stage and As Built SAP?
The design stage assessment is based on the proposed drawings and specification. Its purpose is to establish whether the design is capable of meeting the applicable requirements before construction begins.
It also gives the design team an opportunity to compare different specifications and resolve compliance problems while changes are relatively easy to make.
The as built assessment reflects the dwelling as it was actually constructed. It includes the final products and systems, evidence gathered during construction and the measured air permeability result.
If products or specifications have changed during construction, the assessor must update the calculation.
A dwelling that complied at the design stage may not comply at completion if the final construction differs from the assessed specification. It is therefore important to inform the assessor about changes before products are ordered or installed.
Who Can Carry Out SAP Calculations?
SAP calculations for new dwellings should be completed by an appropriately qualified and accredited On Construction Domestic Energy Assessor.
These assessors are commonly referred to as OCDEAs.
An accredited assessor must follow the requirements of their accreditation scheme and maintain their knowledge through continuing professional development. Their work is also subject to quality assurance.
Vision Energy’s SAP calculations are completed by qualified OCDEAs who are independently registered with Elmhurst Energy.
When Should You Appoint a SAP Assessor?
A SAP assessor should be appointed during the design stage and before the construction specification is fixed.
Early involvement allows the assessor to identify potential issues with the building fabric, glazing, heating, ventilation, thermal bridging and renewable strategy.
If the calculation is completed after construction has started, some of the most practical improvements may no longer be available. This can result in expensive product changes or additional technologies being introduced simply to achieve compliance.
Early calculations can also help coordinate the Building Regulations specification with planning commitments and the project’s wider energy strategy.
You can find more information in our guide to the benefits of completing SAP calculations at design stage.
What Happens if a Design Does Not Comply?
An initial non compliant result does not necessarily mean that the entire design must change.
The assessor should review the calculation and identify the elements that are preventing compliance. They can then test practical improvements and discuss them with the project team.
The solution may involve improving parts of the building fabric, revising thermal bridge details, selecting different windows or changing the heating and hot water specification.
Other options can include improving controls, reducing air leakage or introducing renewable energy.
The appropriate solution depends on the individual project. It should consider construction cost, buildability and long term operation rather than focusing solely on the calculated result.
Our separate guide explains how to pass SAP calculations and resolve common compliance problems.
How Long Do SAP Calculations Take?
The time required depends on the size and complexity of the project, the number of dwellings and the quality of the information provided.
A single house with complete drawings and specifications will normally require less assessment time than a large development containing several house types.
Vision Energy’s standard turnaround is approximately two weeks. This should be confirmed when requesting a quotation, particularly where a project has a fixed Building Control or construction deadline.
Providing complete information at the beginning of the process helps avoid delays.
How Much Do SAP Calculations Cost?
The cost depends on the type and size of the project, the number of dwellings, the number of different house types and the stage at which the assessor becomes involved.
Vision Energy’s fees currently start at £285 plus VAT for an extension SAP calculation or a single new build assessment. EPC lodgement and multi dwelling pricing depend on the project requirements.
Current indicative prices and details of what is included are available on our SAP Calculations service page.
Are SAP Calculations Only About Building Regulations?
Building Regulations compliance is one of the principal reasons for completing SAP calculations, but the assessment can provide wider design benefits.
Early modelling can help compare different construction specifications, heating systems and renewable technologies. It can identify where improvements will have the greatest effect and where expensive measures may provide limited benefit.
Some planning authorities also require developments to achieve an improvement beyond the minimum Building Regulations standard. SAP results can be used to demonstrate performance against these project specific commitments.
The assessment can therefore support design decisions, planning requirements, Building Control approval and the final EPC.
An Example of SAP Calculations in Practice
Vision Energy completed SAP calculations for a development of four new homes on a constrained residential site in North West London.
The work included design stage calculations, U value calculations, thermal bridge assessment, ventilation and heating specification support, and production of the final SAP reports and EPCs.
The project used a coordinated fabric and building services strategy rather than relying on a single technology to achieve compliance.
You can read the full SAP calculations residential project case study.
What Is the Current Version of SAP?
The government identifies SAP 10.3 as the current approved version of the Standard Assessment Procedure as of August 2026.
The Home Energy Model is being developed as a future replacement for SAP. However, the methodology and Building Regulations requirements applying to an individual development can depend on its location, application date, construction dates and the relevant transitional arrangements.
For this reason, the current requirements should be confirmed for each project rather than assumed from the publication date of general online guidance.
Frequently Asked Questions About SAP Calculations
Are SAP calculations required for every new home?
New dwellings normally require an energy assessment to demonstrate compliance with the applicable Building Regulations. The precise process and documentation depend on the location and regulations applying to the project.
Are SAP calculations required for conversions?
They are commonly required where an existing building is converted to create residential accommodation. The assessment route depends on the existing building, the proposed use and the applicable regulations.
Does every extension require SAP calculations?
No. Many extensions can demonstrate compliance by following the normal standards for individual elements and glazing. A SAP based calculation may be required where the proposal departs from this approach, such as an extension containing a large area of glazing.
Can SAP calculations be completed after construction?
An assessment can sometimes be produced for a project that is already under construction or complete, but this can be more difficult. Evidence of the installed construction and building services will be required, and opportunities to make practical improvements may be limited.
Is a site visit required?
Design stage SAP calculations are generally completed from drawings and specifications. The final assessment requires accurate evidence of the completed construction and its systems. The exact evidence and inspection arrangements should be confirmed with the assessor.
Can one SAP calculation cover several dwellings?
Each dwelling must be assessed appropriately, but efficiencies may be possible on developments containing repeated house types. The assessor will review the design variations, orientation and other factors that may affect the results.
Does a better SAP rating guarantee compliance?
No. The SAP rating is only one output. The dwelling must satisfy all the applicable compliance targets and minimum standards.
Is SAP the same as RdSAP?
No. Full SAP is used for detailed assessment of new dwellings and certain other projects. Reduced Data SAP, known as RdSAP, is designed for assessing existing homes where complete construction information is not available.
Arrange SAP Calculations with Vision Energy
Vision Energy provides design stage and as built SAP calculations for individual homes, residential conversions, extensions and multi dwelling developments.
Our qualified OCDEAs work with architects, developers and contractors to provide accurate assessments and practical advice throughout the design and construction process.
Our service includes U value calculations, Building Control reports, specification advice and support through to the final EPC.
Visit our SAP Calculations service page to learn more or request a quotation.
This article was reviewed in August 2026.
Reviewed by: David Barsted, accredited On Construction Domestic Energy Assessor at Vision Energy.