SAP Calculations

SAP Calculations (Standard Assessment Procedure) are used to work out the energy performance of a dwelling and are required for all new builds, as well as conversions and many extensions.

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SAP calculations are a requirement of UK Building Regulations. They are required on all new build properties under UK Building Regulations (Part L1  in England and Wales and Section 6 in Scotland). SAP Calculations are the government-approved methodology to assess the energy efficiency and carbon emission rates for dwellings.

Although most developers will be well versed in SAP calculations, for self-builders and new developers SAP calculations can be confusing and can seem a challenging process. We are here to guide you through the process, right from the design stage to completion – making it a lot simpler for you.

What are SAP Calculations?

SAP calculations are used to formally declare compliance with Part L of the UK Building Regulations. The SAP calculation assesses the energy performance of the dwelling and produces the EPC certificate for the final sale/rental of the property (valid for 10 years), along with the building control compliance documents which are required to be issued your competition certificate.

Part L1A SAP calculations are required on new build dwellings and Part L1B SAP calculations are required on existing buildings subject to a change of use or heavily glazed extension. The requirements differ for each type however the aim of both is to achieve a minimum standard of thermal comfort for the dwelling. 

Residential New Build

Our SAP Process

  • We will review your plans and design specification and complete the design stage SAP calculations.
  • If required, we will provide guidance on how to achieve a pass and we will then issue you with a Predicted Energy Performance Certificate (EPC) and the compliance documents required for Building Control.
  • For a new build dwelling you will require an air tightness test when you near completion. We can carry this out for you at a reduced rate. You can learn more about the air tightness process here.
  • Following the air tightness test, the final building specification will be confirmed and your final compliance documents for Building Control will be issued alongside your EPC.

The process is similar for extensions and conversions however the air tightness test is not a Building Regulations requirement. 

For more information on SAP calculations, scroll down to our FAQ section below. If you have any other questions which aren’t covered, please get in touch.

Frequently Asked Questions

The SAP calculation builds a picture of the energy performance of the dwelling. The following information is included in the assessment:

  • Location
  • Dimensions
  • Orientation
  • Fabric build ups (walls, floors, roofs)
  • U-Values of windows and doors
  • Heating & cooling systems (and controls)
  • Hot water systems
  • Ventilation systems
  • Lighting
  • Renewable energy
  • Air tightness 

Yes. Every new build dwelling in the UK requires one to be carried out. The calculation will ensure that minimum standards have been met or exceeded for all thermal elements while also calculating the carbon emissions for the dwelling and the overall fabric energy efficiency, ensuring that Part L compliance has been achieved. Documents are provided to Building Control to confirm this and an EPC is issued for the dwelling which is valid for 10 years.

Yes, but not all of the time.

SAP calculations for extensions are similar to those for a conversion, as the works will fall under Part L1B (existing buildings) therefore the emissions target, fabric target and air tightness test will not be required.

A SAP calculation will be required if the extension is heavily glazed. Building regulations state an allowance for openings of 25% of the extension floor area, plus the area of openings removed as part of the extension works. Anything beyond this will trigger the requirement for a SAP calculation to be undertaken. 

Generally, we find that most extensions with bifold doors and/or roof lanterns will require one. Walls provide better insulation levels than windows and therefore the calculation is used to ensure that the extension performs to the same level of energy efficiency as it would had it been built within the glazing allowances in Part L1B. To pass the calculation other elements of the extension will need to have been further improved to compensate for the increased glazing levels.


They vary slightly compared to a new build dwelling, as emissions and fabric energy efficiency targets are not required however minimum standards will still be required for each fabric element.

The SAP calculation is carried out to show Building Control that the dwelling has been built (or converted) to the standards set within Building Regulations Part L1B (existing buildings). An air tightness test is not required, however, we do advise that airtightness is considered throughout the build.

Alongside this, we recommend that a test is carried out at the end to ensure the dwelling is energy efficient and there are no hidden leakage areas. Poor airtightness can significantly increase the heat load of a dwelling.

SAP calculations should be carried out in two stages.

The initial calculations should be at the Design Stage, which will ensure that the dwelling specification will satisfy Part L requirements prior to construction. Design Stage compliance documents will be provided which can be forwarded to Building Control.

At completion of the dwelling, once the air tightness test is complete, we will issue the final EPC and the ‘As-Built compliance documents’. These documents should be presented to Building Control.

A common issue we see often is clients who have not carried out SAP calculations prior to construction.  More often than not, when we carry these out at this late stage, they don’t pass at least one of the targets, usually the carbon emissions target if it is a new build dwelling. At this stage, little can be done to remedy the situation which usually results in a hefty bill for PV panels to ‘push’ the dwelling into complying.

If a dwelling isn’t achieving compliance and we have carried out the calculations at the design stage, then there are a whole host of improvements we can suggest that come in at a fraction of the cost of PV panels.

To achieve compliance, there are several minimum standards which need to be met, such as boiler efficiencies and limiting U-Values (the heat loss from a building fabric element).  Alongside those, two target figures need to be met:

Dwelling Emission Rate:
This target is set to ensure the dwelling meets current carbon emission standards. The target figure will be set within the calculation using a notional dwelling with the same size, shape, and orientation of the actual building. It will not be possible to achieve this target by simply meeting the minimum standards detailed in Part L.

Fabric Energy Efficiency:
This ensures the building is built to a high standard in regards to its fabric elements and air tightness. This avoids a poorly insulated building using renewable energy to achieve the overall emissions target detailed above.

The dwelling will also be assessed within the calculation for the risk of overheating although for heavily glazed buildings we advise carrying out full overheating analysis.