Content supplied by Build Aviator

SAP stands for Standard Assessment Procedure, and is the Government’s method for determining the energy and environmental performance of a building, as required for compliance with Building Regulations Part L.

Part L is split into four parts, but for SAP we are only interested in L1a and L1b, which are for ‘New Build’ and ‘Existing Dwellings’.  

Each SAP calculation assesses the CO₂ emissions (DER), as well as assessing the Fabric Energy Efficiency of the dwelling (DFEE).

For renovations to an existing dwelling, chances are you’ll only need an RDSAP, which is a lesser and cheaper version of a SAP. But if you’re building an entirely new property or making major renovations, you’re likely to need a full SAP assessment.

A SAP is a complex calculation, which takes into consideration heat loss through the building fabric (U-Values), and also takes into account hot water demand, boiler efficiency, airtightness and ventilation, amongst other things.

The result will be a U-value, a measure of the heat flow per m² for every 1-degree Kelvin/Celsius in temperature change between the inside and outside of the dwelling.

Build Aviator and their partner assessors are always on hand to confirm compliance can still be met if any changes are made during construction.

Build Aviator and its partner assessors are always on hand to confirm compliance can still be met if any changes are made during construction

Notional values un-associated with products can be used for the SAP assessment rather than product-specific U-values, however, the less specific you are with the SAP assessment at the design stage, the greater the risk of non-compliance once the dwelling has been built. Build Aviator has added a live product library into SAP software, to enable accurate U-values to be created during the as-designed calculations.

At design stage, your designer should provide the architectural drawings and specification to a SAP assessor, who will input this information into software and provide an overall rating. If this doesn’t achieve compliance, the design will need to be revised. This is also required by Building Control prior to work starting on site, so any delays getting the assessment could impact the build start date.

Once construction is underway, any amendments to specification can also cause delays, as these need to be confirmed with the assessor. By using Build Aviator’s product rich SAP assessment, procurement can be advanced, and any availability issues can be addressed prior to work commencing, reducing the risk of such delays.

When the build is complete an airtightness test will need to be carried out, this will then be checked against the as-designed figures and, providing compliance is still met, Building Control will be given the final SAP rating along with an EPC.

Knowing all this about SAP, it’s easy to see why getting a detailed SAP assessment is so important. For more information on the help and expertise available from Build Aviator, visit

Our Sponsors