The Future Homes Standard (FHS) will require all new homes in England to produce at least 75% less carbon emissions than homes built to the 2013 standards. For housing developers, this means heat pumps instead of gas boilers, mandatory solar PV, wastewater heat recovery, tighter airtightness, mechanical ventilation, and a new compliance methodology through the Home Energy Model (HEM). The FHS Impact Assessment estimates an additional build cost of approximately £4,350 per dwelling (weighted average, 2025 prices), and FHS homes will have significantly lower running costs than existing homes, making them more attractive to buyers.
This page summarises the key impacts for developers. For detailed cost analysis, transitional strategy, and procurement guidance, see our Developer Compliance & Cost Guide.
Cost Impact Overview
The additional build cost sits in the services, not the fabric. The table below sets out what changes and where the money goes:
| Element | Part L 2021 (Current) | Future Homes Standard |
|---|---|---|
| Heating system | Gas boiler (~£1,500–2,500) | Air source heat pump (~£5,000–8,000) + hot water cylinder |
| Solar PV | Not required | Mandatory (~£4,000–6,000 for typical 3-bed) |
| Wastewater heat recovery | Not required | Required in the notional dwelling (£475 vertical pipe, £1,426 tray system) |
| Ventilation | MEV or trickle vents (~£300–500) | dMEV (notional) or MVHR; the Impact Assessment carries no ventilation cost uplift |
| Windows | Notional spec 1.2 W/m²K | Same 1.2 W/m²K spec, priced identically in the Impact Assessment |
| Insulation | Notional spec: walls 0.18, roof 0.11, floor 0.13 W/m²K | Same spec, priced identically in the Impact Assessment |
| Airtightness | Standard construction detailing | Enhanced detailing + testing (£5–12 per m², depending on house type) |
These figures are indicative and will vary significantly by house type, volume, and supply chain. Larger developers with established supply chains will typically achieve lower per-unit costs. The cost premium is also expected to reduce as the market scales up heat pump production and solar PV installation becomes routine.
Transitional Arrangements
The government has confirmed a 12-month transitional period from when the FHS comes into force. Understanding these arrangements is critical for planning your pipeline:
- Projects with applications submitted before 24 March 2027 can build to Part L 2021 if commenced before 24 March 2028
- Projects submitted on or after 24 March 2027 must comply with FHS immediately
- 24 March 2028 is a commencement deadline, not a cutover: plots commenced by then are completed under Part L 2021, while plots not commenced lose transitional protection and must meet the FHS
- Transitional arrangements operate on an individual building basis, not site-wide. Different plots on the same site may fall under different regulations
- “Commence” means the foundations and the ground-floor structure are completed (regulation 46A), not merely started
Key Dates for Developers
| Milestone | Date | What It Means for Developers |
|---|---|---|
| Approved Documents published | 24 March 2026 | Final regulations, fabric specs, and transitional arrangements confirmed |
| FHS comes into force | 24 March 2027 | Application deadline for transitional eligibility |
| Transitional period | 24 Mar 2027 – 24 Mar 2028 | 12-month window to commence Part L 2021 projects |
| Transitional commencement deadline | 24 March 2028 | Plots not commenced by this date lose transitional protection |
These dates are now confirmed following the publication of the Approved Documents on 24 March 2026. See our Timeline & Status page for live updates.
Compliance Methodology
FHS compliance is demonstrated by showing that a proposed dwelling performs at least as well as a notional building of the same size and shape. Two methodologies are involved, but not at the same time:
- SAP 10.3: the sole approved methodology at FHS launch on 24 March 2027
- HEM via ECaaS: approved later, using the Home Energy Model's half-hourly dynamic simulation through the centralised ECaaS platform. HEM approval slipped on 8 June 2026 and is now expected in the coming months. Once approved, the two run in parallel for at least 24 months from the statutory instrument, with six months' notice before SAP 10.3 is withdrawn
HEM requires substantially more detailed input data than SAP and runs calculations in under 2 seconds via ECaaS, though the more detailed data entry requirements mean overall assessment time is longer. It provides more accurate modelling of modern technologies, particularly heat pumps and solar PV. For a full comparison, see our Compliance Pathways page.
Frequently Asked Questions
How much more will FHS homes cost to build?
The FHS Impact Assessment estimates an additional build cost of approximately £4,350 per dwelling (weighted average, 2025 prices) over current Part L 2021 compliance. The main drivers are heat pump installation, mandatory solar PV, wastewater heat recovery, and improved airtightness. The notional fabric specification carries over from the 2021 Part L uplift, so the Impact Assessment prices walls, floors, roofs, and windows identically in both. Compared to a typical existing home, annual energy costs will be significantly lower. Compared to a Part L 2021 new build, the difference may be marginal because heat pumps use electricity, which costs approximately four times more per unit than gas.
What is the FHS plot registration deadline?
Projects with applications submitted before 24 March 2027 can build to Part L 2021 if commenced before 24 March 2028. That date is a commencement deadline, not a cutover: a plot commenced in time is completed under Part L 2021, while a plot not commenced by then loses transitional protection. Arrangements operate on an individual building basis, not site-wide. Older transitional provisions (2013 and 2021) have been revoked. See our Transitional Arrangements page for details.
Can developers still install gas boilers under the FHS?
No. The FHS carbon targets are set at a level that gas boilers cannot meet. New homes will need low-carbon heating, primarily heat pumps. Heat networks with low-carbon sources are also acceptable. The FHS is a performance standard and does not name particular technologies, but gas-burning systems, including hybrids and hydrogen-ready boilers, are not expected to reach the targets. During the transitional period, plots commenced under Part L 2021 can still use gas boilers.
What counts as 'commencing' construction for transitional purposes?
Commencement is defined by regulation 46A of the Building Regulations 2010: the sub-surface structure, including all foundations, any basement level, and the structure of ground floor level, must be completed. Starting drainage or excavating foundations is not enough. This is stricter than the guidance applied to the 2021 Part L uplift, which accepted excavation, piling, or building-specific drainage as a start. A plot must reach that point within the 12-month window after the FHS comes into force.
How much will FHS homes save on energy bills?
Compared to a typical existing home, annual energy costs in an FHS home will be significantly lower. Compared to a Part L 2021 new build, the difference may be marginal because heat pumps use electricity, which costs approximately four times more per unit than gas. The low running costs come from heat pump efficiency (2.5–4 units of heat per unit of electricity), mandatory solar PV, a well-insulated fabric, and mechanical ventilation (recovering a minimum of 73% of exhaust air heat per AD L1, with high-performance units achieving 85–95%). As the grid decarbonises, these homes will also become progressively lower-carbon.
Related Pages
Developer Compliance & Cost Guide
Detailed cost analysis, transitional strategy, risk management, and procurement advice.
Transitional Arrangements
Plot registration deadlines, commencement definitions, and strategies for the transition period.
For Builders
What changes on site under the Future Homes Standard: heat pumps, mechanical ventilation, airtightness.
For Architects
How HEM changes design decisions for form factor, orientation, and glazing.