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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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HEM Deepdive: Colours
I’ve been digging into areas of the Home Energy Model which us humble SAP assessors have never had to bother ourselves with previously.
One of the new questions HEM asks is:
What colour is the house?
It asks, because black surfaces absorb more heat than white surfaces.
Jon Ponting
Oct 262 min read
HEM Deepdive: Obstacles
With the Home Energy Model edging towards its official release, I’ve been playing with some of the new inputs to understand how impactful they are on a dwelling’s energy performance.
The first section that will be unfamiliar territory to SAP assessors is Obstacles.
Jon Ponting
Oct 182 min read
New SAP Feature: Electric Showers and WWHRS
A new feature has been unlocked in SAP!
We can now attach Waste Water Heat Recovery systems to electric showers.
The shower has to be an approved Modulating Instantaneous Electric Shower.
Jon Ponting
Oct 112 min read
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
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: WWHRS
We’ve had a few weeks to get under the bonnet of SAP10.3 to understand what a Future Homes Standard compliant home looks like, and we’ve uncovered a strange quirk which works against WWHRS.
To unpick what’s going on in the new SAP methodology, I met up with two of the biggest suppliers of Waste Water Heat Recovery Systems (WWHRS) in the UK: Showersave and ReCoup, at the Keystone Group offices in Derbyshire.
Jon Ponting
May 242 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 - 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
EPC Reform postponed until 2027
Last week, the UK Government (representing England and Wales), and the Scottish Government both released statements saying EPCs will remain unchanged until late 2027.
To recap, the way Energy Performance Certificates look, how results are graded, and the way they are calculated, are all changing. When it happens, it will be the biggest refresh to EPCs since their creation in 2008.
Jon Ponting
Mar 232 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
EPC Reform: The End of rdSAP10 (Yes, already!)
The UK Government has set out plans to replace rdSAP10 assessments with the Home Energy Model.
Domestic Energy Assessors (DEA) are still getting to grips with rdSAP10 (which was only implemented back in the summer) following years of delays.
This consultation also considers how the new EPC metrics will be defined. You’ve got until March 18th, 2026 to have your say.
Jon Ponting
Jan 282 min read
Scotland plans to add PassivHaus to Building Regs
The Scottish Government has outlined plans to update Technical Handbook Section 6 to scrap SAP and further tighten fabric performance standards. They're calling it a 'PassivHaus equivalent standard'.
Specific details and timeframes will be confirmed later this year, with the final ‘Go Live’ date already confirmed as 31st March 2028.
Jon Ponting
Jan 122 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
Wales consults to change SAP, photo evidence and overheating regs
The Welsh Government has released a consultation looking to change Approved Documents Part L, Part O and Part F, following in the footsteps of the Future Homes Standard policy in England.
You've got until 17th November 2025 to respond.
Jon Ponting
Aug 24, 20252 min read
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