What is SAP 10 (and What’s Changing)?

The built environment accounts for approximately 40% of UK greenhouse gas emissions, of which 14% comes from residential homes, according to the Climate Change Committee. If we stand a chance of reaching net-zero by 2050, changes need to happen now.

So, what is SAP 10, and what’s changing? Part L of the Building Regulations is being updated and is due to come into force in June 2022. This will set the path towards the Future Homes Standard 2025, ensuring that new homes produce 75-80% less carbon than homes built under current regulations.

Read on to learn more about SAP 10, and what’s changing.

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What is SAP 10?

SAP 10 will be an update to the methodology used to assess energy usage in new build residential homes and will go live in June 2022, along with the updated Part L Building Regulations.

The new Part L1A targets will see an uplift of 31% carbon saving over the current Part L regulations, and will be assessed against the four-performance metrics:

  • Primary energy
  • Carbon dioxide emissions
  • The Fabric Energy Efficiency Standard (FEES)
  • Minimum standards for fabric and fixed building services

What Changes Will We See With SAP 10?

The updated Part L 2021 has not yet been finalised, but we can have a look at some of the known changes:

Thermal Bridging

Until now we have used Accredited Construction Details (ACDs) to measure thermal bridging, but these will be archived as they are now deemed out of date, and do not meet the new standards. 

From June 2022, we will need to use details from other schemes, or developers will need to consider having the thermal junction modelled to determine the PSI value. 

Not following a scheme or not having the thermal junction calculated will severely impact the calculations and may cause a dwelling to fail the FEES (fabric energy efficiency standard). 

Waste Water Heat Recovery (WWHR) 

WWHR will be added to all showers on the notional dwelling in Appendix R. It reduces water heating by around 10%, so is an excellent way to reduce the heating demand. 

Photovoltaics (PV)

Photovoltaics will also be added to the notional dwelling in Appendix R. Therefore, if PV is not incorporated into the design, we will have to make significant improvements elsewhere in order to gain compliance. We will also be able to input details regarding photovoltaic diverters and battery storage in SAP 10, which will please those thinking about on-site energy storage. 

Electricity Fuel Cost

The carbon factor for electricity will be reduced with SAP 10. It is currently 0.519kgCO2/kWh and will be reduced to 0.136 kgCO2/kWh, which will be only slightly higher than gas. 

The notional dwelling will still be based on gas heating. This will be a welcomed change to so many developers that have wanted to install electric heating but have previously faced hurdles trying to gain compliance under the current SAP 2012. 

house blueprint


Until now, the lighting calculation has been fairly basic. However, SAP 10 will require specific details, including the number of lights per dwelling, and their lumens per watt.

Heating Patterns

Heating patterns will also change as a result of SAP 10. Until now, it has been assumed that the home will be heated for more hours during the weekend, and at higher temperatures. However, the heating pattern will now remain the same for weekdays and weekends, and the temperature for the main living area will be assumed to be at 21°C and the rest of the house to 18°C. The main heating system will be designed for a maximum temperature of 55°C.

 Fabric Performance 

There is a small uplift in the notional u-values for the fabric of the building, including windows, doors and roof lights. 

Air Testing

It will no longer be acceptable to use sample testing. All dwellings will now need to have an air permeability test carried out by a registered engineer with either ATTMA or IATS qualifications.

Dwellings Will Need to be Future-Proofed for Net Zero Carbon

We need to manage the performance gap in our homes in order to future-proof for net-zero carbon in 2050. After consultation, it has been confirmed that the following details will need to be collated:

  • Photographic evidence will now be required for basic elements
  • Details of the insulation levels and type
  • Main and secondary heating system and controls
  • Ventilation systems
  • Evidence of LZC technologies
  • Construction details – images of each thermal junction type
part g compliance

When Does SAP 10 Come Into Effect?

SAP 10 comes into effect in June 2022. There will be a transitional period, but this will be per building, not side wide. To ensure that you build to current Part L1A, the initial notice must have been submitted before June 2022, and work must commence on each building before June 2023.

How can RS Energy Help With Adapting to SAP 10 and Changes to Part L?

At RS Energy, we provide SAP calculations and tailored consulting services that help you achieve compliance efficiently and cost-effectively. Our energy compliance experts will work with you from design to build to ensure that your upcoming projects comply with both SAP 10 and Part L changes.

Learn more about our energy compliance services online today, or get in touch to discuss your project.