SiteKiln gives you plain-English information, not legal advice. If you need advice specific to your situation, talk to your building control body or a qualified energy assessor.
This is the one where regs are moving under your feet. You don't need to be a sustainability guru, but you do need to know where it's heading so you don't design jobs that are obsolete in 2 years.
1. Part L 2021 -- the "stepping stone" you're already on
From June 2022, the 2021 uplift to Part L for new homes kicked in as the next step towards the Future Homes Standard.
For new dwellings this means:
- Around 30-31% lower CO2 emissions required compared with the old 2013 standards.
- A new Target Primary Energy Rate, on top of the carbon and fabric targets -- so the software now checks overall primary energy use, not just CO2.
- Tighter limiting U-values for fabric -- typical limiting values have moved from roughly:
| Element | Old (2013) | New (2021) |
|---|---|---|
| Roof | 0.20 W/m²K | 0.16 W/m²K |
| Walls | 0.30 W/m²K | 0.26 W/m²K |
| Floors | 0.25 W/m²K | 0.18 W/m²K |
| Windows/doors | 2.0 W/m²K | 1.6 W/m²K |
- More focus on as-built evidence -- photos and details of insulation, airtightness measures and junctions must be provided to the energy assessor.
This uplift is explicitly described as the "next stepping stone on the road to a Future Homes Standard and net zero carbon".
2. Future Homes Standard 2025 -- what it's trying to do
Key points:
- New homes built to the FHS from 2025 are expected to produce around 75-80% lower carbon emissions than homes built to the 2013 Part L standards.
- Homes are to be "zero-carbon ready" -- i.e. once the grid is decarbonised, they won't need further significant retrofit to hit near-zero emissions.
- This is achieved through a combination of:
- Low-carbon heating systems (no traditional fossil fuel boilers);
- Much better fabric efficiency and airtightness;
- Attention to overheating and ventilation.
3. Heating -- gas out, heat pumps and low-carbon in
The direction is very clear on heating in new homes:
- Gas boilers will not be permitted in new homes built to the Future Homes Standard from 2025 -- they are effectively banned for new-build under these regs.
- The default heating options are:
- Air source or ground source heat pumps, or
- Low-carbon heat networks (4th-generation, often based on heat pumps).
- Performance requirements for FHS homes are based on notional buildings using efficient air source heat pumps or modern heat networks, not gas or hydrogen boilers.
For existing homes, there is no confirmed phase-out date for gas boilers yet, but for builders doing new housing the play is simple: from 2025, assume no new gas boilers on FHS-compliant sites -- it's heat pumps or equivalent low-carbon systems.
4. Fabric, airtightness and overheating -- what changes on the build side
Common themes
- Better insulation -- walls, roofs and floors with lower U-values than today, moving closer to "fabric-first" spec (thicker insulation, better materials).
- Improved airtightness -- much more focus on sealing gaps, junction detailing, and testing, so homes don't leak heat (and don't suffer draughts that kill heat pump efficiency).
- Thermal bridge reduction -- design and build to minimise cold bridges around openings, junctions and structural elements.
- Ventilation and overheating controls -- the FHS is being brought in alongside tighter standards on ventilation and new overheating rules (Part F and Part O), to stop homes turning into ovens as they get more airtight.
For small builders this means more jobs will demand
- Careful installation of insulation to spec (no gaps/compression).
- Proper taping and sealing around windows, doors, services, and between elements.
- Taking photos and keeping details to prove what you've done for the energy assessor and building control.
5. What this means for you over the next few years
- On new-build homes, expect heat pumps and low-carbon systems to become standard, not "niche green extras", from 2025.
- Fabric specs will keep tightening -- more insulation, better windows/doors, and more pressure on airtightness and workmanship.
- You'll see more emphasis on evidence and sign-off -- photos, airtightness test results, and detailed SAP/Home Energy Model assessments.
- Knowing your way around heat pump-ready systems, good fabric detailing and ventilation will be a competitive advantage -- and makes it easier to work with FHS-ready developers.
The move is to start treating "sustainability" less like an add-on and more like core spec -- it's just becoming part of what "building it right" means on any new house from now on.
6. Common mistakes
- Assuming the Future Homes Standard is years away -- it's 2025; if you're pricing new-build work now, you need to know this.
- Specifying gas boilers on new-build projects -- they won't be compliant under FHS. Switch to heat pumps or low-carbon alternatives.
- Sloppy insulation installation -- gaps, compression and poor detailing that were "fine" under old regs will fail the tighter fabric and airtightness targets.
- Not taking as-built photos -- energy assessors and building control increasingly want photographic evidence of insulation, membrane laps, taping and sealing. No photos = harder sign-off.
- Ignoring overheating (Part O) -- making a house super-insulated and airtight without thinking about ventilation and solar gain creates a different problem.
- Thinking this only affects new-build -- retrofit and extension work under Part L also has tighter requirements. Check the current standards for the work you're doing.
7. Who to contact
- GOV.UK -- Future Homes Standard -- consultation responses and technical guidance: gov.uk/government/consultations/the-future-homes-and-buildings-standards-2023-consultation (free)
- Building Control -- your local authority or approved inspector for Part L compliance queries (free)
- Energy assessors -- for SAP calculations, Home Energy Model assessments and as-built evidence: find via CIBSE or Elmhurst Energy (paid)
- MCS -- for heat pump installer certification: mcscertified.com
- CITB -- training on energy efficiency, heat pumps and new building standards: citb.co.uk (free guidance)
8. Sources and legislation
- Building Regulations 2010 (as amended) -- Part L (conservation of fuel and power). legislation.gov.uk/uksi/2010/2214
- Approved Document L -- Volume 1: Dwellings (2021 edition) -- current Part L guidance for new dwellings: gov.uk/government/publications/conservation-of-fuel-and-power-approved-document-l
- Approved Document O -- Overheating (2022) -- new overheating requirements: gov.uk/government/publications/overheating-approved-document-o
- Approved Document F -- Ventilation (2021 edition) -- updated ventilation requirements: gov.uk/government/publications/ventilation-approved-document-f
- Future Homes Standard 2023 consultation -- government proposals and technical detail: gov.uk
- Climate Change Act 2008 -- net zero 2050 target underpinning all of this. legislation.gov.uk/ukpga/2008/27
9. Related guides on this site
- 10.6 Upskilling in green construction -- heat pumps, EV charging, retrofit
- 7.14 MCS certification -- heat pumps and renewable installations
- 7.15 TrustMark registration -- what it is and whether you need it
- Building Regulations: Part L -- conservation of fuel and power
- Building Regulations: Part F -- ventilation
- Building Regulations: Part O -- overheating
- Building Regulations: Part S -- EV charging infrastructure
- Building Regulations: Future Homes Standard
Know someone who needs this?
Was this guide useful?
Didn't find what you were looking for?
Spotted something wrong or out of date? Email us at hello@kilnguides.co.uk.
In crisis? Samaritans 116 123 ·