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SAP 10 is coming for your house type…

With current events, it is easy to forget that Part L is soon to see a long overdue change and while we can’t know exactly when it will now be implemented (October this year was the idea), we do know that SAP 10.1 gives a good idea of how houses will need to be designed to pass Building Regulations in the near future.


How is SAP 10 different from the current SAP 2012?                         

It’s SAP Jim but not as we know it!


SAP 10.1 is the latest update to the well established ‘SAP’ methodology for assessing dwellings for their energy efficiency credentials. While the update cannot be used in an official capacity, it was published to allow designers to plan ahead. SAP10.2 will most likely be the official version for the new Part L.


Currently, we use SAP 2012 and have done for 7+ years so it is easy to see that this is now long in the tooth. Crucially, the national grid is a lot greener than it was seven years ago which means that SAP 2012 is overestimating the CO2 emissions for any fixed building services that use electricity.


Another criticism of SAP 2012 is its accuracy at representing how energy will be used by a dwelling, as well as how well the design is being built onsite. Future SAP assessments will be more detailed in how they calculate building energy use and in the audit trail of how designs and constructions are assessed and verified.


Part L Changes

There are several changes which are due to be implemented and it would be nice to say to boldly go where no man has gone before with the new changes. However, based on the government preferred option as below, you will see the updates are uninspiring.


Firstly, a new performance target with Primary Energy being the number criteria to meet which is putting the CO2 emissions as the secondary target. There are two options on the table for the CO2 emissions, these being:


  • Option 1 – 20% reduction in CO2
  • Option 2 – 31% reduction in CO2


The fabric energy efficiency standard used under the current Part L 2013 will be removed in the new SAP 10, Part L 2020. There will be much stricter compliance checks, no more tick boxes. All dwellings will need to be evidenced properly with photos and possibly invoices. There will also be improved guidance provided for developers.

For air testing, we currently carry out 3 of each dwelling type of 50%. Under the new Part L, all dwellings will need to be air tested.

There will also be a new affordability standard through the EPC, details yet to be confirmed.


What does this mean for housing design?

Predominantly, it updates carbon emissions, recognising that electricity is now less carbon intensive than before. Therefore, electricity will compare more favourable to gas systems. Heating systems powered by electric will be more viable, especially highly efficient heat pumps. As we have seen with the increasing shift form fossil fuel car engines to electric, we will begin to see the emphasis in housebuilding and be less gas boiler centric. Below is a list of some other significant changes that will come with SAP 10:  


  • SAP assessments will pay more attention to detail on a range of design aspects. Lights will be assessed based on lumen efficiency and in tandem with solar gains, which means that window specification will have an even greater bearing than before.


  • Thermal bridging will no longer be about implementing tick box lists of standard accredited construction details, instead requiring more compensation for using worst case defaults or having detailed PSI calculations done by a qualified engineer.


  • Hot water demand will now include the number and type of showers and baths, meaning hot water will have a much bigger impact in the SAP calculation. As a result, shower heat recovery or solar hot water may be needed as standard.


  • PV technology will include for battery storage and flats will now only see the CO2 and cost savings if they each have a direct connection rather than just to the landlord’s side.


  • Thermal mass will be assessed in greater detail. Rather than a generic three option input, detailed calculations will be needed, in turn, influencing the way the dwelling fabric is deemed to respond to energy.


Overall, in Option 1 and 2 as above, the SAP calculation will be much harder to achieve SAP compliance. If using a gas or electric heating system a lot more measures will be required, such as higher fabric standard, a combination of mechanical ventilation with heat recovery and shower heat recovery, plus possibly PV too. However, if a heat pump is installed, such as an air source or ground source heat pump, this will make it much easier to pass the SAP 10 calculation. We have also investigated SAP 10 in quite some detail and if an ASHP is used for both space and water heating, the fabric specification can actually be worse off than current Part L 2013 regulations. This being highly illogical said Spark.


Part L Timetable

Below shows the timeline we are working to for the changes to be implemented. However, this will likely be delayed due to the current situation we are in at present with COVID-19.


Date Governments Option on timing
Late 2019/20 More consultation on


Standards for existing dwellings

Standards existing and new non-domestic


Early/Mid 2020  

Publication of new Part L, Part F and overheating, guidance documents


Mid/Late 2020 Part L, Part F and overheating to come into force


How can I adapt to SAP 10?

Be prepared to provide the right information and in enough detail. The earlier you can think about the specification of your development and provide the information to an assessor, the more ahead of the curve you will be. It is best not to leave the SAP calculations until build is near, or worse, underway. Consider energy efficiency from the earliest stages, and get your designs developed and assessed so any issues can be ironed out.


If you prefer designs around gas boilers, know that it is likely you will need high standards in most other aspects as well as ‘bolt-on’ renewable technology. Opting for no PV or wanting to scale back on things like thermal bridging will require the use of low carbon heating, such as heat pumps. There are also useful tech options, which are often overlooked but helpful, such as waste water heat recovery, gas savers on boilers etc.


How can Base Energy help with my designs and SAP 10?

Our experienced consultants have been anticipating the official introduction for SAP 10 for some time now. Since SAP 10.1 has been released, we have already worked with clients to assess their regular house types against the new criteria in order to tweak and optimise specifications.

We are also offering free online CPDs on the new SAP 10 and 2020 Building Regulations.


If you would like to discuss your house designs or SAP needs with one of our specialist consultants, please call us on 020 3286 2016 / 0151 933 0328 or email


By Allan Jones – Sustainability Consultant

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