# Working in Wales - energy, Part L and Future Homes
Think of Welsh Part L as a close cousin of the English version, not a twin. Same basic idea - cut carbon, tighten up fabric, push low-carbon heating - but different documents, different timings, and potentially different numbers.
If you design or price straight off English Part L for a Welsh new build, you're guessing. And guessing on U-values and SAP targets is how you end up re-insulating walls or swapping kit at your own expense.
1. The rulebook: Welsh Part L, not English
Both countries call it "Part L - Conservation of fuel and power," but:
- Wales has its own Part L Approved Documents, published by Welsh Government.
- These set the Welsh standards for energy performance, U-values, boiler/heat pump efficiency, air-tightness, etc.
- The front covers and references are different to the English ones - you want the ones clearly marked for Wales.
For any Welsh new build or big refurb, you and your designer should be asking:
- "Are we definitely using the Welsh Part L volumes?"
- "Have we checked the dates - are we on the current Welsh version, not an old England PDF?"
If the answer is "I just Googled Part L and grabbed the first one," that's not good enough for Welsh work.
2. Different Future Homes timelines
England and Wales are not marching in lockstep towards the Future Homes Standard.
- England has its own timetable and interim uplifts.
- Wales has its own timetable, with its own staged tightenings of Part L.
- At any given point, a Welsh new build might be working to different performance levels than an English one started at the same time.
You don't need every date in your head. You just need to stop assuming "whatever England's doing this year is what Wales is doing too."
On a real job:
- Confirm with the designer/SAP assessor: "Which Welsh Part L version and start date are you designing this to?"
- Make sure building control in Wales agrees you're on the right side of any changeover.
3. U-values, targets and SAP - Wales has its own numbers
The detail that bites your profit lives in:
- Notional building specs (the benchmark your design is compared against)
- U-values for walls, roofs, floors, windows and doors
- Air-tightness targets
- Primary energy / CO2 targets or similar headline metrics
- Heating and hot water system expectations
For Wales:
- The notional spec and target values in the Welsh Part L guidance and SAP setup may not match the English ones.
- A wall that "passes" in England could fail in Wales, or vice versa.
- The SAP assessor must run the job as Wales, using the Welsh target set.
Your job is to:
- Check the SAP report says "Wales" in the jurisdiction/regs field.
- Build exactly to the specs in that Welsh-based report - insulation thicknesses, window performance, heating, PV, air-tightness level.
- Flag to the design team if their spec doesn't match what's actually been priced.
If your SAP assessor uses the England setup by habit, you can end up with a design that looks compliant on paper but falls over when a Welsh building control officer checks it.
4. How to handle Welsh Part L on a live job
Build these steps into your normal routine:
On the job file
Write: "Energy regs: Welsh Part L (Wales)."
At the start
Tell the designer/SAP assessor: "This is in Wales - design and run SAP to Welsh Part L, not England."
Before you price
Ask for the SAP design report early and check:
- It clearly shows Wales as the jurisdiction.
- The spec you're pricing (insulation, glazing, systems, PV) matches that report.
At key stages
Sanity-check against the Welsh SAP spec at envelope closed, first fix, and pre-completion - not an old English crib sheet.
Welsh Part L - 60-second checklist for builders
1. Confirm the country on day one
Write on the job file: "Energy regs: Wales - Welsh Part L." Say it out loud to the designer/SAP: "This is Wales, not England."
2. Get the right paperwork
Ask the designer/SAP assessor:
- "Are you using the Welsh Part L Approved Document(s)?"
- "Have you set the job to Wales in your SAP software?"
Don't accept "it's just Part L, it's all the same" as an answer.
3. Lock the spec to the Welsh SAP report
Before you finalise price or place big orders, get the design-stage SAP report for Wales. Check your spec/quote matches it on:
- Wall, roof, floor insulation thickness and type
- Window and door U-values
- Heating system (boiler vs heat pump, controls, cylinders)
- Any PV or renewables shown
- Air-tightness target
If what's on the SAP and what's in your quote don't line up, stop and sort it before you sign anything.
4. Build to the Welsh numbers, not your habits
On site, make it someone's job to check:
- Materials delivered match the spec in the Welsh SAP (not "what we usually use in England").
- Installers know the air-tightness target and the details they can't shortcut (tapes, seals, foam, etc.).
- Any changes (value-engineering, swapping kit) get re-checked with the SAP assessor.
- No silent swaps just because a merchant had something cheaper on the shelf.
5. Keep Welsh Part L visible
- Save the Welsh Part L PDF and SAP report in the job folder and on everyone's phone/tablet.
- Mark any printed extracts "Wales - Part L" in big letters so they don't get mixed with English sheets.
- At handover, keep a copy of the Welsh SAP and compliance paperwork with your O&M pack.
Pin this up: the van one-pager
- Is the job in Wales? Write "Welsh Part L" on the file.
- Tell designer/SAP: "Run it as Wales, not England."
- Get the Welsh SAP report before pricing properly.
- Match insulation, windows, heating, PV and air-tightness to that report.
- Don't swap specs without checking the SAP again.
You follow that, and you stop leaking profit on failed tests and last-minute upgrades just because someone quietly used the wrong Part L in the background.
What to do next
- Read: Working in Wales - building regulations differences
- Read: Working in Wales - planning rules
- Read: SiteKiln Building Regulations Part L guide (England)
Sources (UK)
- Welsh Government - Welsh Part L Approved Documents, energy performance standards.
- Future Homes Standard - separate English and Welsh implementation timelines.
- SAP (Standard Assessment Procedure) - jurisdiction-specific settings for England vs Wales.
- Building Regulations 2010 (as applied in Wales) - shared framework, Welsh-specific implementation.
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