What Part L 2026 changes
The Building Regulations are the legal minimum standard for construction in England. Part L — Conservation of fuel and power — sets the energy and carbon performance requirements. Until 24 March 2027 the relevant version is Part L 2021 (delivered via the interim June 2022 uplift); from that date the Part L 2026 amendment, implementing the Future Homes Standard, takes over.
The change is not a tweak. Part L 2026 mandates a 75% CO₂ reduction versus the 2013 baseline — compared with the 30% delivered by Part L 2021 — and adds, for the first time in UK Building Regulations history, a functional requirement for on-site renewable electricity generation.
The 5 Ws of Part L 2026
When does it apply?
From 24 March 2027 for any new dwelling where the Building Control application is submitted on or after that date. A 12-month transitional period applies for projects that have commenced before 24 March 2027 — they may continue to be built to Part L 2021 until 24 March 2028. Higher-Risk Building provisions follow on 24 September 2027.
What are the key technical requirements?
- Requirement L1 (Conservation of fuel and power) — minimum fabric U-values and air permeability tightened (see table on the FHS guide).
- Requirement L2 (Limiting unwanted heat gains) — works with Approved Document O (overheating).
- Requirement L3 (NEW — on-site electricity generation) — solar PV at 40% ground floor area coverage, deemed-to-satisfy.
- Heating system — no fossil-fuel boilers in new dwellings; ASHP or heat networks only.
- Compliance engine — Home Energy Model replaces SAP.
Why has it been introduced?
The Climate Change Act 2008 commits the UK to net zero by 2050. Buildings account for ~25% of UK emissions and new construction at 2021 standards still locks in fossil-fuel heating that would require expensive future retrofit. The FHS approach — "zero carbon ready" — solves the problem at point of construction so that, as the electricity grid decarbonises (already over 65% low-carbon in 2025), buildings become zero-carbon without further intervention.
Who is responsible?
Compliance is the responsibility of the person commissioning the work — usually the developer or, for self-builds, the homeowner. Designers, contractors and Building Control bodies all play roles. SAP/HEM assessors (Elmhurst, Stroma, BRE) issue the compliance modelling. Energy Performance Certificates remain the on-completion artefact for buyers.
Where does it apply?
England. Wales runs parallel regulations following a similar timeline; Scotland's Section 6 of the Building Standards already requires direct-emission-free heating from April 2024 and is consulting on PV mandates. Northern Ireland's Technical Booklet F2 has not yet adopted FHS-equivalent provisions.
Practical compliance pathway
For a developer or contractor delivering new homes from 2027, the practical compliance flow looks like this:
- Design stage — house type drawings updated with fabric performance, ASHP and PV array per the 40% rule.
- SAP/HEM modelling — assessor runs HEM (or SAP 10.3 during transitional period) to demonstrate Dwelling Emission Rate (DER) ≤ Target Emission Rate (TER).
- Building Control application — Full Plans or Building Notice including the compliance pack.
- Site delivery — fabric installed to designed U-values, air-permeability test on completion, PV and ASHP commissioned, MID-metering installed.
- As-built HEM — final HEM updated with as-built values; EPC issued.
- Building Control sign-off — completion certificate issued; warranty providers (NHBC, LABC, Premier) confirm cover.
Our SAP & HEM Compliance Modelling service handles steps 2, 5 and the technical inputs to 3 and 6 — typical same-week turnaround on a 3-bed/4-bed standard house type.