With the timeline now firmly set for the introduction of the Future Homes Standard (FHS), developers across England are carefully considering the best approaches to consistently reach compliance. The standard is an update to Part L (2021) of the Building Regulations and is intended to ensure that all new homes are net zero ready. Much of the focus in this latest update surrounds the mandatory use of low carbon heating and requirement for photovoltaics (PV) on most roofs. However, with these systems sized tightly to maximise cost efficiency, ensuring both the insulation specification and detailing are well considered and accurately carried through to the finished build is essential. Without this, homes may fail to perform as expected and compliance may be put at risk.
Understanding the FHS
The FHS was published at the end of March 2026. To support developers in preparing for the new requirements, phased transitional arrangements have been introduced. These requirements will generally apply from 24th March 2027 unless the relevant building control application was submitted before that date and the development has been sufficiently commenced before 24th March 2028, in accordance with the transitional provisions. Separate transitional arrangements apply for Higher Risk Buildings (HRBs), aligned with the Gateways process for those projects.
The most notable changes under the FHS relate to building services. As expected, homes are now strongly geared toward low carbon heating systems such as heat pumps or low carbon heat networks, rather than traditional gas boilers. In most cases, they will also require significant roof-mounted solar PV provision, often broadly equivalent to around 40% of the property’s ground floor area (although alternative compliance approaches are possible).
A new modelling methodology — the Home Energy Model (HEM) — is also being introduced. This includes a number of measures, such as modelling energy use at half hourly timesteps, which should help improve accuracy at the design stage. As HEM has not yet been fully approved for regulatory compliance, the existing SAP methodology has been updated (SAP 10.3) and will continue to operate in parallel for 24 months following HEM implementation.
As in previous editions, a Notional Dwelling specification is provided. This is applied to a theoretical building of the same dimensions as the proposed home within the energy modelling software to generate the performance targets (primary energy, carbon emissions and fabric energy efficiency) for the dwelling. Developers are free to vary from this specification, provided they meet the required performance targets, limiting values (such as worst-case U-values) and any other mandatory requirements.
The U-values for the walls, floors and roof within the updated Notional Dwelling (shown below) are unchanged from the existing regulations. However, there are good reasons for developers to pay close attention to the building fabric, both during the design and build stages.
With the shift to low carbon heating, retaining heat effectively becomes increasingly important. Technologies such as heat pumps generally operate most efficiently at lower flow temperatures than conventional boilers. Where homes have higher heat losses, larger heat emitters and/or higher flow temperatures may be required to maintain comfort, particularly during colder weather. This reduces heat pump efficiency and increases electricity use at the very point where external temperatures, peak heating demand and, for some homeowners, electricity prices are highest.
This is particularly important under the FHS as many developers will look to optimise system sizing to manage upfront costs, leaving less tolerance for unexpected heat losses or poor as-built performance. Alongside good system design, commissioning and controls, robust fabric performance and detailing therefore become increasingly important in supporting efficient low temperature heating systems.
To support good fabric performance, the FHS retains the Fabric Energy Efficiency Standard (FEES) approach used under previous editions of Part L. FEES sets a target level of fabric performance for the dwelling and is influenced by factors including U-values, airtightness, thermal mass, thermal bridging and solar gains.
Modelling carried out under SAP 10.3 suggests that improving floor and wall U-values can support FEES compliance, but this must be accompanied by careful junction detailing. High heat losses at these junctions (represented as psi-values) can make compliance difficult to achieve. As a result, developers will increasingly need calculated thermal bridge details for key junctions, supported by robust and buildable design solutions.
In addition, BREL compliance reports introduced under Part L 2021 require developers to provide photographic evidence to Building Control showing that these details have been correctly delivered on site across each dwelling.
Specifying and Designing Insulation
When selecting insulation to achieve efficient fabric performance, a key point to consider is the thermal conductivity of the product. The lower this value is, the more effective it will be at preventing heat loss. This can allow a specific U-value to be reached with a slimmer thickness of insulation than might be possible with worse performing alternatives.
Phenolic insulation boards achieve some of the lowest thermal conductivities of commonly used insulation products — as low as 0.019 W/mK. This can offer advantages across a wide range of applications, including cavity walls, where efficient fabric performance can often be achieved within 100 mm or 125 mm cavities, helping preserve internal floor space within a given footprint. This can become increasingly important where developers also need to accommodate additional plant space associated with low carbon heating systems, such as hot water cylinders. Phenolic insulation can also provide a premium thermal performance solution for floors, compared to other commonly used alternatives with a higher thermal conductivity – potentially removing the need to excavate to accommodate the insulation.
To support good practice, some manufacturers offer services covering both design and on-site delivery. This can include calculated thermal bridge details for specific insulation systems at key junctions to help reduce psi-values and support FEES compliance. Manufacturers may also provide on-site product awareness training for installation teams, covering key regulatory requirements, insulation options and good installation practice to help ensure details are correctly delivered on site.
A Firm Foundation
Whilst much of the focus following publication of the FHS has been on low carbon heating systems and renewables, robust fabric performance remains essential both for compliance and to support real-world building performance. By delivering efficient fabric performance alongside good junction detailing, developers can reduce heat losses, support efficient operation of low temperature heating systems and provide greater resilience against site variation and as-built performance gaps.