FHS Published: What Actually Changed From Consultation to Final Standard

The Future Homes Standard has been published, but the final documents look notably different from the December 2023 consultation proposals. Some changes were expected. Others were genuine surprises. This article analyses the ten most significant shifts between what was consulted on and what was actually published, drawing on the government's formal consultation response published on 24 March 2026. If you want a broad overview of the FHS itself, start with our complete FHS guide. This piece is specifically about what changed, and why.

Solar PV: The Biggest Shift

The most significant change from consultation to publication is the treatment of solar PV. The 2023 consultation proposed including solar panels in the notional building specification: south-facing, covering 40% of the ground floor area, at 20% efficiency. Under this approach, PV would have been an assumption in the compliance calculation. Builders who could meet the carbon targets through other means (better fabric, more efficient heating) could theoretically have avoided installing panels entirely.

The final standard takes a fundamentally different approach. Instead of a notional building assumption, the government has created a new functional requirement: Requirement L3. This makes on-site renewable electricity generation a standalone legal obligation for all new dwellings, entirely separate from the energy performance calculation. You cannot trade your way out of it.

The consultation response explains why. Respondents argued that a south-facing, 40%-of-ground-floor-area specification was impractical for many dwelling types and site layouts. North-facing plots, complex roof geometries, and high-density developments would have struggled to replicate the notional building PV specification, potentially penalising designs that were otherwise highly efficient. By making PV a functional requirement with flexible sizing guidance, the government addressed these concerns while strengthening the overall obligation.

The sizing guidance specifies 0.22 kWp/m² over 40% of the ground floor area, or a practicable roof area approach where site constraints apply. There is a minimum generation threshold of 720 kWh per year. Higher-risk buildings (flats over 18 metres or seven storeys) are exempt entirely. For more on how HEM models solar PV performance, including self-consumption and battery storage, see our technical guide.

SAP 10.3 and HEM: A Phased Approach

The 2023 consultation positioned the Home Energy Model as the replacement for SAP, with the expectation that HEM would be the compliance methodology when the FHS launched. That is not what happened.

Instead, the government has created SAP 10.3 as a bridging methodology. SAP 10.3 will be the sole approved compliance tool when the FHS comes into force in March 2027. HEM will follow a minimum of three months later, subject to receiving approved methodology status. Once HEM is approved, a 24-month dual running period begins, during which either SAP 10.3 or HEM can be used. The government will give at least six months' notice before withdrawing SAP 10.3.

The consultation response is candid about the reasons. Industry raised concerns about the readiness of the HEM ecosystem: the complexity of the model, the absence of approved software tools, and the time needed for assessors and software vendors to adapt. Rather than force an untested system on the industry at the same time as the most significant fabric and heating standards upgrade in a generation, the government opted for a staged transition. SAP 10.3 is essentially SAP 10 updated with the new FHS fabric values, carbon factors, and compliance metrics.

For SAP assessors, this means the immediate priority is SAP 10.3 readiness. But the direction of travel is clear: HEM will eventually become the sole methodology. The dual running period gives the industry time to build confidence in HEM without risking compliance deadlines.

Transitional Arrangements: The Longer Option

The consultation offered two options for transitional arrangements. Option 1 was shorter, Option 2 was longer. In a telling decision, the government chose Option 2 despite 77.8% of consultation respondents supporting the shorter approach.

Under the final arrangements, the FHS comes into force on 24 March 2027. Projects with a building notice, initial notice, or full plans application submitted before that date can build to current Part L 2021 standards, provided building work commences before 24 March 2028. Higher-risk buildings have a later start date of 24 September 2027. For a full breakdown of the transitional rules, see our transitional arrangements guide.

The government's reasoning centres on giving the supply chain adequate preparation time. Heat pump manufacturers, ventilation installers, solar PV suppliers, and the wider construction workforce all need time to scale up. The longer transitional period also reduces the risk of bottlenecks, where a rush of applications submitted just before the deadline creates a surge of Part L 2021 projects that delays the shift to FHS standards.

The practical effect is that some homes will still be built to current standards well into 2028. Developers with large sites and existing planning consents have a window to continue as before. But the sunsetting of older transitional provisions (from 2013 and 2021) means this is genuinely the last extension. Plots that were still relying on 2010 standards under legacy arrangements must now meet the FHS if work has not commenced.

Fabric and Compliance Changes

Beyond the three headline changes, several technical adjustments in the final standard caught the industry by surprise. These are smaller individually, but together they reflect a pattern: the government tightened some rules, relaxed others, and removed several workarounds that the consultation had left open.

Average Compliance for Terraces Removed

The consultation had considered allowing terraced housing to demonstrate compliance on an average basis across a row. The final standard removes this option entirely. Each dwelling must individually meet all three compliance targets: the Target Emission Rate (TER), the Target Primary Energy Rate (TPER), and the Target Fabric Energy Efficiency (TFEE). Mid-terrace units, which benefit from shared party walls, can no longer subsidise less efficient end-terrace units within the same row. This is a significant change for volume housebuilders who design terraces as a single building type.

Thermal Bridging Default Removed for HEM

Under current SAP methodology, designers can use a default y-value for thermal bridging if they do not have calculated junction values. The final standard retains this default for SAP 10.3 but removes it for HEM. When HEM becomes the approved methodology, all thermal junctions must be individually modelled or calculated from published details. This pushes designers towards better thermal bridge detailing and makes fabric performance modelling more rigorous under HEM.

Heat Network Sleeving Period Extended

The consultation proposed a three-year sleeving period for heat networks, the period during which a communal heating system can operate before needing to demonstrate compliance with low-carbon requirements. The final standard extends this to five years. This gives heat network operators and developers more time to transition from gas-fired communal systems to low-carbon alternatives, recognising the complexity and cost of retrofitting district heating infrastructure.

dMEV Ductwork 2m Limit Removed

The consultation proposed a hard limit of 2 metres on ductwork runs for decentralised mechanical extract ventilation (dMEV) systems. The final standard removes this arbitrary limit and replaces it with a requirement for competent person verification on runs over 2 metres. This is a pragmatic change: many real-world installations require longer duct runs, and a rigid 2-metre cut-off would have been difficult to achieve in certain building layouts. The competent person requirement ensures quality without unnecessarily constraining design.

No Chimney or Flue Without Secondary Heating

The final standard prohibits the installation of a chimney or flue in a new dwelling unless it serves a secondary heating appliance. This closes a loophole where homes could be built with decorative chimneys or “just in case” flue provisions. Given that the primary heating system must be low-carbon (typically a heat pump), installing chimney infrastructure for a future gas or wood fire contradicts the intent of the standard.

Non-Domestic Lighting Efficacy Reduced

One change worth noting on the non-domestic side: the consulted lighting efficacy requirement of 150 lm/W has been reduced to 105 lm/W in the final standard. Industry feedback argued that 150 lm/W was not achievable across all luminaire types, particularly in specialised applications. The reduced target is still a significant step up from current standards while remaining achievable with modern LED technology.

What Stayed the Same

Not everything changed. Several core elements of the consultation proposals made it through to the final standard largely intact:

• The 75% carbon reduction target compared to 2013 standards proceeded as consulted
• Heat pumps remain the default low-carbon heating solution in the notional building
• The three compliance metrics (carbon emissions, primary energy, and fabric energy efficiency) are retained
• The notional building approach continues as the compliance framework
• Airtightness targets and ventilation requirements are broadly as consulted
• The ban on fossil fuel heating in new homes is confirmed through the performance standards, as expected

One notable non-change: the government decided not to proceed with a Future Homes Standard brand. Homes built to the new standard will not carry a specific FHS label or certification mark. The consultation had explored this idea, but the final decision was to let the Building Regulations framework speak for itself rather than creating a separate branding regime.

What This Means for the Industry

The pattern across these changes is pragmatic adaptation. Where the consultation proposed rigid specifications (south-facing PV, 2-metre duct limits, HEM from day one), the final standard introduces flexibility while often strengthening the underlying obligation. Solar PV went from a tradeable assumption to a legal requirement. Thermal bridging defaults disappeared for HEM. Individual dwelling compliance replaced terrace averaging.

For developers, the immediate task is understanding how these changes affect current projects and design specifications. The longer transitional period provides breathing room, but the sunsetting of legacy provisions means this is genuinely the final opportunity to build under pre-FHS standards.

For designers and specifiers, the individual dwelling compliance requirement and the removal of thermal bridging defaults under HEM point towards more detailed modelling and better detailing. The days of relying on default assumptions and averaging across a terrace row are ending.

For energy assessors, the phased SAP 10.3 to HEM transition means there is no immediate cliff edge. But the direction is clear, and those who begin familiarising themselves with HEM now will be ahead of the curve when dual running begins.

For the latest key dates, see our Timeline & Status tracker.

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