The Future Homes Standard was first proposed by government in 2019. Despite plans for implementation in 2025, as of the time of writing, the final details of the now renamed Future Homes and Buildings Standard (FHBS) have yet to be confirmed. C ompared to a home constructed to Part L 2013, the FHBS should deliver new homes that emit 80% less carbon emissions compared to homes built to Part L 2013 regulations. These homes are intended to be built to a performance level that will not require further retrofitting to meet operational net zero targets as the electricity grid continues to decarbonise. Parallel proposals are being developed for new non-domestic buildings.
Based on various official statements, the FHBS will happen. Current consultation documents provide a strong indication of the likely scope of the standard. In an October 2024 blog post rebutting claims that low-carbon building standards would be watered down, MHCLG said: “The final standard has yet to be determined but will be shaped to ensure that new homes can be designed in keeping with local architectural practices, while also balancing energy bills, emissions, energy demand and construction costs.”
WHAT DOES THE FHBS INCLUDE?
The question of what makes a building sustainable, net zero and/or fit for the future is a complex one. Even restricting the definition to energy efficiency and carbon emissions is not clear-cut. Does it mean upfront carbon, operational carbon or whole-life carbon? Is the way building occupants use the building (‘unregulated energy use’) included in the definition? Then there is the question of climate adaptability and whether buildings will be useable in the face of rising temperatures and more extreme weather.
The 2023 Future Homes Standard consultation outlined what was in and out of the scope of the proposed regulation changes. Embodied carbon was not part of the scope, nor was unregulated energy use. Likewise, water efficiency, biodiversity and nature recovery – all elements of a ‘more sustainable’ built environment – were all out of scope.
Changes already implemented via the 2021 Building Regulations updates include improved building fabric (including insulation), higher-specification windows to reduce heat loss, lower air permeability, and the introduction of low-carbon heating and hot water systems such as heat pumps. The proposed
FHBS consultation builds on these measures. Despite the extent of changes introduced in 2021, and expected to be introduced in the near future, there are concerns with the FHBS. CIBSE has expressed concerns around airtightness, ventilation, compliance targets and measures to address the performance gap.
The key requirements for meeting the FHBS listed below are taken from what has been proposed so far by the government, but may be subject to change once the FHBS officially launches.
BUILDING FABRIC EFFICIENCY
• Walls, floors and roofs to achieve improved insulation U-values.
• Reducing draughts by sealing gaps in the building fabric will be key to minimising heat losses and improving airtightness.
• Structural weaknesses where heat can escape must be addressed to maintain energy performance to reduce thermal bridging.
HVAC AND RENEWABLES
• The FHS proposal encourages low-emission alternatives, such as heat pumps, for space heating, hot water and comfort cooling.
• Direct-emission fossil fuel heating systems, such as natural gas boilers, are not expected to meet compliance under the proposals.
• While not a regulatory requirement, designers may consider incorporating features that enable future installation of renewable technologies such as solar PV systems. This could include provision for roof space, suitable structural design, and cable routing to facilitate later system installation, where appropriate.
• The use of mechanical extract ventilation (MEV) or mechanical ventilation with heat recovery (MVHR) may be specified to achieve compliance with ventilation requirements while maintaining airtightness.
THERMAL INSULATION
The FHBS sets the minimum level of performance that homes and buildings will need to meet. Clients, designers, specifiers and contractors will be free to exceed those minimums if they wish, but achieving better is impossible without understanding the starting point. The 2021 regulatory updates, and the energy efficiency proposals of the FHBS, constitute a more holistic approach to building specification and construction. For many, however, their entry into understanding the standards will be the answers to the questions: What U-values do I need to achieve? What thickness of insulation will those U-values require?
Perhaps surprisingly, the building fabric standards proposed for Part L 2021 were not radically different from what immediately preceded it in Part L 2013. Insulation is inherent to every element of a building, from ground floor to external walls to roof structures. However, beyond certain points, increasing insulation thickness delivers diminishing returns, and regulatory compliance depends on multiple interacting design factors. Instead, differences lay in areas like thermal bridging, airtightness and achieving as-built performance.
To achieve the kind of carbon reductions required in 2021 and 2025, vs the 2013 baseline, renewable technology became a crucial part of performance specifications, in addition to good building fabric standards. Solar PV, air source heat pumps and waste water heat recovery all represent viable routes to making compliance achievable, complementary to familiar U-values.
The shift to lower U-values from Part L 2013 to Part L 2021 was not as pronounced as might have been expected, and the FHBS is not expected to improve them further. However, the changes to the compliance model under the FHBS are expected to result in tighter fabric specifications in practice. This is because reduced flexibility in trade-offs will require more designs to achieve or approach the notional fabric performance.
There is one area in which real-world fabric specifications could change substantially. Despite the notional wall U-value for new dwellings expecting to remain at 0.18 W/m²·K, external walls could see relatively big leaps in U-value.
Walls tend to have the biggest surface area of all the building elements, especially in semi-detached and detached properties. To keep building footprints down and to avoid reducing internal footprint, developers have tended to prefer thinner wall constructions – but the changes in regulations are impacting on insulation specifications for external walls. This has been borne out by real world efforts to understand the implications of the FHBS.
The Future Homes & Buildings Standard sets the minimum performance levels that homes and buildings will need to meet.
MASONRY CAVITY WALL INSULATION
Low building fabric U-values for floors and roofs are current practice, but thicker wall constructions will likely be an outcome of the FHBS. How walls are insulated, and how that insulation interacts with adjoining elements, is key to delivering a building that performs to the FHBS – in theory and in practice.
As the predominant form of wall construction in UK housebuilding, specifying and detailing masonry cavity walls to deliver buildable constructions with low U-values and minimal thermal bridging is key. Indicative compliance modelling suggests that wall thicknesses may increase beyond 350mm, and in some cases approach 400mm, depending on the insulation type, blockwork specification, and design approach adopted to meet or improve upon the notional 2021 U-values.
Where maintaining thinner cavity widths remains a priority, lower thermal conductivity insulation materials such as rigid polyisocyanurate (PIR), SOPREMA’s Thermaclass Cavity Wall 21, for example, with declared thermal conductivity of 0.021 W/m·K, can enable the same U-value target of 0.15 W/m²·K to be achieved with cavity widths typically around 125mm, depending on the full wall specification. The BBA-certified product features a thermal conductivity of 0.021 W/mK. Installation can be with a 10mm residual cavity to accommodate mortar squeeze, or as a full fill solution with no residual cavity, giving project-specific options to suit the requirements of specifiers and installers. Installation can be visually inspected during construction, allowing photographic evidence to be captured for compliance documentation where required under Part L.
The installation can be checked on site to avoid gaps between boards in the main wall areas. Care can also be taken to ensure that junction details, such as where a roof meets the top of a cavity wall, are constructed correctly to deliver continuous insulation – vital for achieving as-built performance.
The nature of blown cavity insulation in newbuild homes is that the inner and outer leaf masonry must be complete before the insulation can be installed. Unlike rigid board systems, cavity fill installations occur after both masonry leaves are complete, making visual inspection during installation more challenging. www.soprema.co.uk