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The HEM-line blog
The Home Energy Model (HEM) is a new way of forecasting the energy performance of residential buildings in the United Kingdom. In the coming years, HEM will replace the Standard Assessment Procedure (SAP) for generating Energy Performance Certificates (EPC) and checking compliance with Part L / Section 6 of Building Regulations.
HEM is currently in development. When it is approved for use, this blog will include tutorials and advice for how to use the new calculation tool.
While we're waiting, you can browse through this archive of my LinkedIn articles, covering changes to Building Regulations, Energy Performance Certification, national planning policy, and everything in between.
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Elmhurst Cardiff Conference 2026
Plenty of thoughts still to digest after last week's Elmhurst Wales Conference in Cardiff.
Great speakers, great venue, and very well organised. Top marks!
Jon Ponting
Oct 41 min read
Tweaks on the way for SAP10.3
Just six months to wait until the new Part L (the Future Homes Standard) goes live in England.
Five changes to the new methodology are under review with a fix expected before the end of the year. In some cases, these changes could affect existing SAP10.3 results.
Jon Ponting
Sep 302 min read
Part L 2026 - Revisions
If you’ve already downloaded your own copies of the Future Homes Standard and Future Buildings Standard (Part L 2026), do it again! There’s been some amendments.
Nothing too serious, just a few corrections and clarifications. All the big headlines (such as amount of PV and fossil fuel free requirements) remain the same.
Jon Ponting
Sep 271 min read
Part L 2026 PV requirements - FAQs
Since the new Approved Document Part L (the Future Homes Standard) was published, there's been uncertainty about the specifics of the new PV Functional Requirement.
We now have answers to some of those Frequently Asked Questions from the MHCLG.
Jon Ponting
Sep 131 min read
SAP10.3 Oddities: Exhaust Air Heat Pumps
To comply with the Future Homes Standard, most new homes will require a heat pump. Apartment complexes might look at Exhaust Air Heat Pumps, but it seems the new SAP10.3 calculator isn’t so keen on those. I've been down a SAP rabbithole to find out why.
Jon Ponting
May 312 min read
SAP10.3 Oddities: Low Air; Don't Care
SAP10.3, which checks homes are compliant with the Future Homes Standard, does a very strange thing with air leakage results. You could have an air test of 1.5 or 4.5, and your fabric performance (FEE) won't change.
Logically, a house with a better air tightness will lose less heat, so you’d expect the fabric performance to score better. That’s always been the case in previous versions of SAP.
Jon Ponting
May 172 min read
New Part L for Wales (Extensions and Non-Resi)
Part L2 (2026) in Wales introduces Photographic Evidence for non-domestic buildings.
Also, a new tier of requirements has been added to the Consequential Improvements rule for residential extensions in Wales, bringing a touch of Future Homes Standard to the renovation market.
Jon Ponting
May 142 min read
New Part L for Wales (Onsite generation)
Here are some further details about the changes to Approved Document Part L (Wales), which closely follows the Future Homes Standard targets which apply to England, but are scheduled to come into force three weeks earlier; being applied to new building sites from 4th March 2027. This post focuses on the new requirement for onsite energy generation.
Jon Ponting
May 122 min read
New Part L for Wales (Targets and Notional)
This revised Approved Document Part L will apply to any building work where the relevant building inspector accepts applications from 4th March 2027.
Any unstarted buildings on existing sites after 4th March 2028 will need to meet the new regs, regardless of when the site was submitted.
As with the current Part L, most of the English (UK) and Welsh versions are identical, but there are a few curveballs developers need to be aware of.
Jon Ponting
May 102 min read
FHS Launch - Mandatory solar panels
One part of the Future Homes Standard has grabbed the media’s attention more than most: Mandatory solar panels on all new homes. But how will these new regs work in practice?
Jon Ponting
Apr 12 min read
FHS Launch - Fabric performance
Now the Future Homes Standard and Part L (2026) have been published, we can begin unpicking what compliance looks like for new building sites across England.
Changes to the fabric performance targets are under the spotlight this morning, or lack of changes may be more appropriate.
Jon Ponting
Mar 292 min read
FHS Launch - When does it apply?
When will the Future Homes Standard apply?
For most developments, we have a full calendar year to get ourselves ready. The new Part L goes live on 24th March 2027.
This is defined as the date the developer submits documents (initial notice, building notice, application with full plans) to the relevant building authority.
If paperwork is submitted and accepted before 24th March, the site can built to the 2021 (current) regs.
Jon Ponting
Mar 262 min read
HEM User Guides updated
A fresh set of Home Energy Model User Guides have been published - this will be particularly useful for manufacturers of domestic heating, cooling, hot water, ventilation and renewable systems.
Jon Ponting
Mar 161 min read
Future Homes Standard Update for Wales
The Senedd has published its response to last year's Approved Document Part L consultation, confirming new energy standards for building sites from 2027.
Strictly speaking, FHS doesn't apply in Wales, but this news broadly follows what we're expecting from the UK Government in the coming weeks.
Jon Ponting
Mar 92 min read
NPPF Consultation Launched
A newly written National Planning Policy Framework (NPPF) for England has been published and is open for public consultation.
The draft text aims to stop local authorities from setting their own emissions targets, and recommends councils look more favourably on developments that take a proactive approach to the net zero transition.
Jon Ponting
Jan 52 min read
HEM - Outputs and Troubleshooting
When a SAP calculation spits out unexpected results, the assessor can look through the worksheets and, 99% of the time, they can find the reason and fix it. The Home Energy Model doesn’t produce simple worksheets that assessors can scrutinise, and it doesn’t have a single methodology you can thumb through. So how will we troubleshoot in HEM?
Jon Ponting
Nov 17, 20252 min read
New HEM Technical Documents published
This is only going to be exciting for us high-level Home Energy Model nerds, but new Home Energy Model Technical Documents have just been published on the DESNZ website.
These docs explain the logic behind HEM.. a bit like the SAP methodology manual.
Jon Ponting
Nov 10, 20252 min read
HEM to replace SAP - Confirmed by UK Government
When the FHS consultation was released in December 2023, there were two other consultations hidden in its shadow. This week's publication is the official response to one of those lesser-spotted policy proposals.
In a nutshell, it confirms SAP is definitely going to be retired. HEM will take over as the method for complying with Approved Document Part L. It will also be used for calculating Energy Performance Certificates.
Jon Ponting
Oct 5, 20251 min read
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