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Future Homes Standard U-values — the new fabric performance targets — UK new build solar PV installation
Future Homes Standard

Future Homes Standard U-values — the new fabric performance targets

Every U-value change under Part L 2026: external walls down to 0.15, ground floor to 0.11, roof to 0.11, doors to 1.0, air permeability to 3. With practical buildup examples.

FHS U-Values for Walls, Floors, Roofs & Windows — Future Homes Standard guidance for new builds

The fabric specification under Part L 2026 is materially tighter than the 2021 standards. Three numbers matter most: wall U-value of 0.15, ground floor 0.11, and air permeability of 3. Hitting these on a volume housebuilder programme is achievable but requires deliberate detailing.

Why fabric tightening matters more than ever

Part L 2021 delivered a 30% CO₂ reduction vs 2013, mostly through small fabric improvements and notional PV. Part L 2026 needs 75% — and a heat pump can only do so much. The fabric envelope must be excellent for an ASHP-heated home to operate efficiently and for the dwelling to remain comfortable through the larger glazing areas typical of modern designs.

New wall U-value: 0.15 W/m²K

Down from 0.26. Achievable in masonry construction with full-fill cavity (mineral wool or PIR) at 150 mm. Timber frame typically uses I-joists with 250 mm insulation between studs. SIPs panels at 200 mm hit the figure comfortably.

New ground floor U-value: 0.11 W/m²K

Down from 0.18. Demands 200–250 mm of PIR or EPS below the slab, or a structurally insulated raft. The change drives heavier groundworks but improves long-term comfort.

New roof U-value: 0.11 W/m²K

Down from 0.16. Either 350 mm of mineral wool between rafters (with a cold loft strategy) or 200 mm of PIR for warm roof construction. In-roof solar arrays integrate cleanly with PIR warm-roof builds.

New air permeability target: 3 m³/(h·m²)

Down from a maximum of 8 — and from a typical built value of 5–6. Hitting 3 requires deliberate detailing of every penetration: services, eaves, party-wall junctions and windows. MVHR becomes effectively required at this air-tightness level to manage moisture and CO₂.

External door U-value: 1.0 W/m²K

Down from 1.6. Composite or insulated timber doors at this rating are now commonplace; this is one of the easier upgrades to specify.

40% of ground floor area
PV / ground floor area
Mar 2027
FHS in force
75%
CO₂ vs 2013 baseline
£4,350 per dwelling
Per-plot premium
For developers and housebuilders

Fhs u-values for walls, floors, roofs & windows for volume new-build programmes

Per-plot pricing locked at procurement. Factory pre-fit on panelised roof cassettes. SAP/HEM modelling for every house type included. NHBC, LABC, Premier and Buildmark warranty-accepted workmanship. 20-year insurance-backed system warranty. We work with developers from 50 plots to 5,000+ across multi-site frameworks — agreed pricing, agreed programme, agreed warranty stack.

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For self-builders and architects

Fhs u-values for walls, floors, roofs & windows for one-off custom builds

Engagement from RIBA Stage 2. PV sizing collaborative with the architect. SAP/HEM modelling that gives the architect freedom on glazing ratios and roof geometry. Building Control submission pack ready for the Approved Inspector. 0% VAT on new-build dwellings. Staged invoicing aligned to your self-build mortgage drawdowns. We work with custom-build buyers across England, Wales and Scotland.

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How this fits into the FHS compliance pathway

Every FHS-compliant new build must pass three regulatory gates. Fhs u-values for walls, floors, roofs & windows fits primarily into the second gate — design-stage Part L compliance — but has knock-on implications for Building Control sign-off and post-completion warranty:

  1. 1
    Planning permission Most solar PV on new dwellings is consented within the dwelling\'s primary planning consent. Conservation Areas, Article 4 directions and listed-curtilage plots require additional planning consideration — we handle the planning evidence required for these.
  2. 2
    Building Control — Part L compliance SAP 10.3 or HEM compliance modelling demonstrating Dwelling Emission Rate ≤ Target Emission Rate. PV specification, ASHP capacity, fabric U-values and air permeability all entered into the modelling. We provide the full compliance file ready for the Approved Inspector.
  3. 3
    Post-completion — warranty & EPC MCS certificate, EPC, monitoring app onboarding and 20-year insurance-backed workmanship warranty. NHBC, LABC, Premier and Buildmark all accept our installation specification without query — important if you\'re relying on a structural warranty for buyer mortgageability.

For a fuller walkthrough of the compliance process, see our Part L 2026 page and the FHS PV calculator which sizes a compliant system from your ground floor area in 30 seconds.

Frequently asked

Common questions

Answers to the questions we get most often when discussing fhs u-values for walls, floors, roofs & windows with new clients.

When does the Future Homes Standard come into force?
24 March 2027 in England, with a 12-month transitional period running to 24 March 2028 for projects already under construction. The Approved Documents L and F were published on 24 March 2026 (Government statement HCWS1445), giving the industry exactly 12 months of certainty before regulatory commencement. Scotland, Wales and Northern Ireland are following with broadly equivalent regulations on roughly aligned timetables, although devolved nuances apply — Welsh regulations are typically 6 months ahead.
What does FHS-compliant solar PV actually cost per plot?
The Government Impact Assessment puts the total FHS premium at ~£4,350 per dwelling per dwelling (2025 prices, weighted average across heat pump, solar PV, MVHR and enhanced fabric). Of that, solar PV is roughly £4,200 — covering ~3.4 kWp for a typical 3-bed semi (panels, in-roof mounting, inverter, monitoring, MCS certification and 20-year insurance-backed warranty). Larger dwellings cost proportionately more; volume procurement reduces per-plot cost by 20–25%.
Will the 40% PV rule actually be enforced?
Yes — the rule is a functional requirement in the Approved Document, not guidance. Building Control sign-off requires SAP/HEM modelling demonstrating compliance. The previous Part L 2021 token "2-panel" systems no longer pass, since they fall ~85% below the 40% benchmark. The deemed-to-satisfy route requires the full 40%; alternative compliance through enhanced fabric is possible but rarely cost-effective.
Can I exceed FHS minimum specifications?
Yes — and many self-builders and premium developers do. Marginal capital cost of a larger array (e.g. 5 kWp instead of 3.4 kWp on a 3-bed) is only £1,000–£1,200, while the additional generation pays back in 3–4 years at 2026 electricity tariffs. Upgrades that fit easily on top of an FHS-compliant base include battery storage (£3,500–£5,000), larger array size, EV charge point pre-fit (£600) and air permeability below 2 (achievable with deliberate detail).
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More on the Future Homes Standard

The 40% Ground Floor Area PV Rule Explained →

Part L 2026 requires solar PV coverage equal to 40% of the ground floor area. We break down exactly what that is, how to calculate it for any house type, and when the rule can be relaxed.

Future Homes Standard 2026 / 2027 Timeline →

The complete FHS rollout timeline — from the 24 March 2026 publication of the Approved Documents through to the 24 March 2028 end of the transitional period. Includes practical milestones for developers.

Gas Boiler Ban in New Builds: 2027 Rules →

From 24 March 2027 the Future Homes Standard makes gas, oil, LPG and hydrogen-ready boilers non-compliant in new dwellings. We explain why, what replaces them, and the impact on plot pricing.

FHS Cost Impact: £4,350 Per Dwelling Decoded →

The Government Impact Assessment estimates an average £4,350 per dwelling FHS premium. We break it down by line item (solar PV, ASHP, MVHR, fabric, doors) and show how it varies by house type.

FHS Transitional Period: What Pre-2027 Projects Can Do →

Projects that commence Building Control approval before 24 March 2027 may complete to Part L 2021 standards until 24 March 2028. We explain the rules and the practical implications.

FHS Rules for Flats and Apartments →

Flats present geometry problems: roof area is shared, ground floor area is variable. We explain how Part L 2026 allocates the 40% PV rule between flat owners and the Higher-Risk Buildings rules.
FHS 2027 deadline approaching

Get an FHS-compliant solar quote in 48 hours

Tell us your plot details — ground floor area, location and target start-on-site date. We return a fully-costed system sized to Part L 2026 (40% PV rule), with the SAP/HEM compliance pack included.

Get my free quote Try the FHS calculator 📞 0330 088 5421