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How SAP and HEM change under the Future Homes Standard — UK new build solar PV installation
Future Homes Standard

How SAP and HEM change under the Future Homes Standard

Part L 2026 replaces SAP with the Home Energy Model (HEM) — a half-hourly dynamic simulation. We explain how HEM differs, what it means for assessment time, and the transitional rules.

SAP & HEM Changes for FHS Compliance — Future Homes Standard guidance for new builds

The Standard Assessment Procedure (SAP) has been the UK's domestic energy compliance methodology since 1992. Part L 2026 retires it for new dwellings, replacing it with the Home Energy Model. This page explains how HEM differs and why it matters for designers.

Why SAP is being replaced

SAP runs on monthly steady-state assumptions and does not realistically model self-consumption, batteries, EV charging or smart heating controls. As renewable technologies became central to compliance, SAP's limitations became significant. HEM resolves them by running half-hourly dynamic simulation over a full year.

How HEM differs

HEM models the dwelling 17,520 times per year (every 30 minutes). It tracks solar generation against demand profile, battery state of charge, EV charging schedules and ASHP COP variation with outdoor temperature. The output is more realistic — and rewards the design choices (battery, smart controls) that actually deliver bill savings.

Assessment time impact

Typical SAP assessment time on a 3-bed house: ~20 minutes. Typical HEM assessment: ~1 hour 40 minutes. SAP/HEM consultancies are recruiting and retraining; expect HEM modelling charges to be 2.5–3× legacy SAP for the first 18 months of the transition.

Software status

Elmhurst, Stroma, BRE and NHER have HEM implementations either released or in late beta as of mid-2026. The Government's reference HEM toolset is also available for verification. Practices need a HEM-capable workflow before March 2027.

Transitional rules for assessors

During the 24 March 2027 – 24 March 2028 transitional period, projects qualifying for transitional protection may use SAP 10.3. After that, HEM is the only valid compliance route. Energy Performance Certificates continue to be issued through HEM outputs.

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

Sap & hem changes for fhs compliance 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

Sap & hem changes for fhs compliance 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. Sap & hem changes for fhs compliance 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 sap & hem changes for fhs compliance 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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FHS PV Calculator

Enter your ground floor area — get the 40%-rule minimum kWp, panel count and indicative cost in 30 seconds.

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Plot details, postcode and target start-on-site — we return a fully-costed FHS-compliant package within 48 hours.

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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 U-Values for Walls, Floors, Roofs & Windows →

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 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 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.

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