Standard Assessment Procedure (SAP): Past, Present, and Future
With recent announcements on the Standard Assessment Procedure (SAP) and Home Energy Model (HEM) being able to be used to assess compliance with the Future Homes Standard, we take a look at how the national calculation methodologies have evolved and what we expect to see in the coming years.
The History of SAP
SAP was developed by the BRE and was based on the Domestic Energy Model (BREDEM). The first version of SAP was released in 1993 and has been updated periodically since. These changes have introduced refinements to the core physics of the model, revised cost, carbon and energy factors and recognition of new technologies that have come to market. We take a look back at how SAP has developed over the years and what changes have come into effect:
1994
SAP was cited in the Building Regulations in England as the means of assessing the energy performance of dwellings.
2002
For the first time Part L allowed compliance for new homes to be demonstrated by using SAP to calculate carbon emissions.
2006
The Building Regulations introduced the requirement to limit the amount of carbon emissions from new dwellings by using SAP 2005 to calculate a Target Emission Rate. This still remains within Part L today. SAP 2005 also saw the introduction of heat losses from linear thermal bridging, calculation of lighting energy demand and overheating risk required by Part L 2006.
2007
SAP 2005 was updated to reflect the introduction of On Construction EPCs. This included incorporating Mechanical Ventilation and Heat Pumps into the PCDB. It also saw the introduction of calculations for wind turbine and small scale hydro electricity generation.
2010
SAP 2009 was introduced alongside Part L 2010. This introduced party wall heat loss into the model as well as thermal mass and space cooling demand/energy use.
2013
SAP 2012 was introduced alongside Part L 2013 and was used to calculate the newly introduced Fabric Energy Efficiency Standard. SAP 2012 saw the introduction of thermal bridging junctions between roof elements and additional primary pipework heat loss options.
2022
Finally, after a decade since the last update, SAP 10 was introduced alongside Part L 2021 in 2022. SAP 10 introduced PV diverters and batteries into the methodology. It also contained changes to the calculation of PV generation, lighting and domestic hot water energy demand calculations.
The Limitations of SAP in a Modern World
SAP was originally designed to be completed using pen and paper (and handheld calculator) by an assessor on site. This required that the model be very simple compared to the modern industry standard. As we have seen over the course of its life, updates to SAP have improved aspects of the methodology and revised input assumptions, but the fundamental underlying workings have remained. SAP is therefore limited in its ability to model modern dwellings and technologies.
The dawn of the Home Energy Model
As a result of this in November 2023 the Department of Energy Security and Net Zero (DESNZ) released two consultations introducing a new energy rating methodology known as the Home Energy Model. The Home Energy Model has been developed from scratch using alternative sources to SAP and has the potential to be used in a much broader set of applications. The Home Energy Model is intended to replace SAP to calculate compliance with the Future Homes Standard and produce Energy Performance Certificates. It is likely that Wales, Scotland and Northern Ireland will also utilise HEM in future revisions to their own Building Regulations and Standards.
However, in May 2025 the Government announced that an updated version of SAP 10, known SAP 10.3, will be able to be used to demonstrate compliance to the Future Homes Standard alongside the Home Energy Model. This will not only ensure that HEM is fully ready before being launched but will give OCDEAs more time to prepare and learn the new methodology.
For dwellings being assessed on SAP 10 today it is expected that they will still use SAP to produce their as built compliance reports and EPCs. Therefore, SAP will remain actively used for a number of years after HEM has been introduced.
Elmhurst Thoughts
New Build Dwellings Manager Jason Hewins commented;
“Over the next couple of years the industry is entering a period of unprecedented change in terms of Building Regulations and the national calculation methodology that supports them. SAP has been used to demonstrate compliance with Building Regulations for over twenty years and many assessors have experience of numerous versions of SAP in their careers. However, HEM will eventually take over from SAP and its vital the surrounding items for SAP such as conventions are revisited for the implementation of HEM.
There will likely be a number of years where On Construction Domestic Energy Assessors will be using both SAP and HEM due to how the transitions in Building Regulations work. Elmhurst are ready to support our members during this unprecedented time of change through thorough clear guidance, support and training.”