What it is
The Future Homes and Buildings Standard (FHS) is the next generation of Building Regulations energy requirements for England, and the biggest change to new-build standards since Part L was last fundamentally rewritten. It requires new homes to produce at least 75% less carbon than a home built to 2013 standards — a step far beyond the 30-31% cut delivered by the Part L 2021 uplift.
The aim is homes that are zero-carbon-ready: low-carbon heating (in practice, heat pumps or heat networks), high fabric standards and on-site renewable generation, with no reliance on fossil fuels. A zero-carbon-ready home isn’t zero-carbon on day one — it’s designed so it becomes net-zero as the electricity grid decarbonises, needing no retrofit along the way.
The timeline
The final Approved Documents (new editions of Approved Document L Volumes 1 and 2, and Approved Document F Volume 1) were published on 24 March 2026, alongside the government’s response to the 2023 consultation and Building Circular 01/2026.
| Milestone | Date |
|---|---|
| Approved Documents published | 24 March 2026 |
| FHS comes into force (most work) | 24 March 2027 |
| Deadline to apply under Part L 2021 | 24 March 2027 |
| FHS in force for higher-risk buildings | 24 September 2027 |
| Transitional projects must have commenced | 24 March 2028 |
A 12-month transition period protects projects already in the pipeline — more on the detail below — after which the FHS applies in full.
The four big changes
1. Low-carbon heating — the effective end of the gas boiler
The FHS doesn’t “ban” gas boilers by name. Instead the 75% carbon reduction target is set at a level no fossil-fuel system can meet — so hybrid boilers and hydrogen-ready boilers won’t comply either. In practice that means air source or ground source heat pumps, or connection to a low-carbon heat network, in the vast majority of new homes.
This only affects new homes. Existing properties are unaffected: you can still install or replace a gas boiler in an existing house. The government estimates FHS homes will save households up to £830 a year versus a typical EPC-C property — though, honestly, savings against a Part L 2021 new build are more marginal, since heat pump electricity still costs roughly four times as much per unit as gas.
2. Enhanced fabric — tighter U-values across the board
The FHS keeps a whole-building performance approach, so you can trade off between elements. One point catches people out: SAP 10.3 and the Home Energy Model each have their own notional dwelling specification, calibrated differently but aiming at the same overall standard. Here’s how the headline notional U-values compare with Part L 2021:
| Element | Part L 2021 | FHS notional (SAP 10.3) | FHS notional (HEM) |
|---|---|---|---|
| External walls | 0.26 | 0.18 | 0.15 |
| Ground floor | 0.18 | 0.13 | 0.11 |
| Roof | 0.16 | 0.11 | 0.11 |
| Windows | 1.6 | 1.2 | Based on actual dimensions |
| Doors | 1.6 | 1.0 | 1.0 |
| Airtightness | 8.0 (max) | 4.0 | 3.0 |
U-values in W/m²K; airtightness in m³/(h·m²) @ 50 Pa. See our U-values guide for what these mean in practice.
One thing that doesn’t change: junction thermal bridging stays central to the fabric calculation. Calculated Ψ-values (see ΨMonkey) remain the best alternative to penal default values under both SAP 10.3 and HEM — and with tighter fabric everywhere else, well-detailed junctions matter more, not less.
3. Mandatory solar PV — a genuine first
This is the headline everyone missed in the earlier drafts. A new functional requirement L3 makes on-site renewable generation a legal requirement of Building Regulations — the first time English regs have mandated renewable generation outright, rather than merely assuming it in the notional dwelling.
The rule: rooftop PV equivalent to 40% of the dwelling’s ground-floor area (AD L1 para 5.73), or a “reasonable amount” where shading or orientation genuinely constrain it.
That 40% sounds unchanged from SAP 10 — but there’s a catch. The conversion factor from roof area to installed power has changed from 1/6.5 (about 153 Wp/m²) to 1/4.5 (about 222 Wp/m²), reflecting more efficient modern panels. So while the headline number looks the same, the actual generation required has risen by roughly 45%. For most detached and semi-detached homes that means a 3–4 kWp system.
Exemptions apply for buildings over 18 metres tall, higher-risk buildings, and sites where a minimum output of 720 kWh per year can’t be achieved — for example due to heavy shading or awkward roof geometry. See our solar PV guide for how it earns its keep in a compliance calculation.
4. Ventilation and airtightness — Part F tightens too
The much tighter airtightness targets mean mechanical ventilation becomes effectively unavoidable in most FHS homes, whether decentralised mechanical extract (dMEV) or MVHR for the heat-recovery benefit. The updated Approved Document F also changes how systems are signed off:
- All new ventilation systems must be commissioned by a competent person scheme member.
- Powered flow hoods are now mandatory for commissioning; rotating vane anemometers are prohibited.
Poorly commissioned ventilation has been a persistent problem in airtight new builds, and these changes are a direct response. They sit alongside completion-stage air tightness testing, which becomes more important than ever as targets drop.
The notional dwelling: two routes to the target
The published documents offer two notional dwelling options, both delivering the same carbon target with a different balance of airtightness and ventilation:
| Specification | Option 1 (MVHR) | Option 2 (Natural ventilation) |
|---|---|---|
| Airtightness | Tighter (~4 m³/h·m²) | Looser (~5 m³/h·m²) |
| Ventilation | dMEV / mechanical | Natural ventilation |
| Waste water heat recovery | Required (WWHRS) | Not required |
| Solar PV | Required (L3) | Required (L3) |
| Low-carbon heating | Required | Required |
How compliance is assessed: SAP 10.3 now, HEM later
Compliance is demonstrated the familiar way — showing your dwelling performs at least as well as a notional building of the same size and shape. Approved Document L 2026 retains the three Part L 2021 metrics: primary energy rate (DPER), carbon emissions rate (DER) and fabric energy efficiency (DFEE). No simplification — compliance stays multi-dimensional.
At launch, assessment is via SAP 10.3, an updated version of the familiar SAP methodology. The government’s new Home Energy Model (HEM) — a complete replacement for SAP that models performance at half-hourly intervals — was expected to follow around three months after publication, but was delayed again on 8 June 2026. As things stand, SAP 10.3 is the sole approved methodology, with HEM expected in the coming months, followed by a dual-running period before it eventually replaces SAP entirely.
HEM is a bigger shift than the version number suggests: it demands far more data than SAP (early testing suggests a house type takes around 1h40 in HEM versus roughly 20 minutes in SAP), with punitive defaults where data is missing, and it will be delivered through a single central calculation service rather than competing third-party engines. We’re tracking every software release closely.
What it costs
The government’s impact assessment puts the extra build cost at roughly £4,350 per dwelling (weighted average, 2025 prices) — or in the region of 3–8% per home — driven mainly by the heat pump, solar PV, extra insulation and mechanical ventilation. That’s offset by lower running costs and no gas standing charge, and the premium is expected to narrow as heat pump and PV supply chains scale up. Expect a surge in demand for both as the deadline approaches, so procurement planning matters.
Transitional arrangements
The 12-month transition runs from 24 March 2027 to 24 March 2028, and it’s stricter than previous uplifts:
- Projects with an application submitted before 24 March 2027 can build to Part L 2021 — if work commences before 24 March 2028.
- “Commence” includes drainage and foundation work, not just superstructure.
- Arrangements operate on an individual-building basis, not site-wide, so different plots on the same site can fall under different regs.
- Older 2013 and 2021 transitional provisions — which still let some large sites build to 2010 standards — have been revoked. Any uncommenced plots relying on them must now meet the FHS.
What to do now
Projects gaining planning consent from here on will most likely be built under the FHS — so design for it now: heat pump heating, strong fabric, mechanical ventilation planned from the start, and solar PV sized to L3. Get the thermal bridging detailed properly while the drawings are live, and don’t fix a specification for 2027 starts before you’ve stress-tested it against the numbers.
We’re tracking the secondary legislation and software releases closely — talk to us before you lock in a spec, and we’ll tell you where the risks are.
Frequently asked questions
When does the Future Homes Standard come into force?
The Future Homes Standard comes into force on 24 March 2027 for most building work, and 24 September 2027 for higher-risk buildings. The Approved Documents were published on 24 March 2026. A 12-month transition means projects with an application in before 24 March 2027 can still build to Part L 2021 if work commences before 24 March 2028.
How much solar PV does the Future Homes Standard require?
New dwellings must install rooftop solar PV equivalent to 40% of the dwelling’s ground-floor area under new functional requirement L3. Because the area-to-power conversion factor has changed from about 153 Wp/m² to about 222 Wp/m², the actual generation required has risen by roughly 45% even though the 40% headline is unchanged. This typically means a 3-4 kWp system. Exemptions apply for buildings over 18 metres, higher-risk buildings, and sites that cannot achieve a minimum output of 720 kWh per year.
Are gas boilers banned under the Future Homes Standard?
Not banned by name, but effectively yes for new homes. The standard requires a 75% cut in carbon emissions versus 2013 standards, a level no fossil-fuel system can meet, so hybrid and hydrogen-ready boilers do not comply either. Heat pumps or low-carbon heat networks become the default. Existing homes are unaffected: you can still install or replace a gas boiler in an existing property.
What U-values does the Future Homes Standard require?
The notional dwelling U-values differ slightly between the two compliance routes. Under SAP 10.3 they are roughly 0.18 W/m²K for walls, 0.13 for ground floors, 0.11 for roofs, 1.2 for windows and 1.0 for doors. The Home Energy Model notional is tighter still, at about 0.15 for walls and 0.11 for floors. Both are a significant step beyond the Part L 2021 figures of 0.26 for walls and 0.18 for floors.
Will Future Homes Standard compliance use SAP 10.3 or the Home Energy Model?
SAP 10.3 only at launch. The Home Energy Model (HEM) was expected around three months after publication but was delayed again on 8 June 2026, so SAP 10.3 is currently the sole approved methodology. HEM is expected in the coming months, followed by a dual-running period before it eventually replaces SAP entirely.
How much more do Future Homes Standard homes cost to build?
The government’s impact assessment estimates around £4,350 of additional build cost per dwelling, or roughly 3-8% per home, driven mainly by the heat pump, solar PV, extra insulation and mechanical ventilation. This is offset by lower running costs and no gas standing charge, and the premium is expected to narrow as supply chains scale up.
Does the Future Homes Standard apply to existing homes?
No. The Future Homes Standard applies only to new dwellings in England. Existing homes are not required to retrofit to FHS standards, and gas boiler replacements remain legal in existing properties. Standards for conversions and material changes of use are being kept under separate review.