The construction industry is still working through the detail of the Future Homes Standard (FHS), with new homes expected to comply within the next 12 months. Approved Document L (ADL) was released in 2021 to prepare for the transition, but the publication of Approved Document L: Energy and Greenhouse Gas Emissions 2026 marks another significant update.
The revised guidance tightens performance requirements, expands compliance obligations and places greater emphasis on proving that buildings perform as designed. For architects and specifiers, the changes affect everything from heating strategy and roof design to cavity widths and site reporting.
Low-carbon heating and renewables
The headline changes are the new requirements around low-carbon heating and on-site renewable energy generation.
Although gas boilers have not been formally banned, the emissions targets in ADL 2026 make it difficult to achieve compliance without heat pumps or other low-carbon systems. Solar generation is also expected to become standard on new homes. The guidance states that photovoltaic panels should cover an area equivalent to at least 40% of the building’s ground floor area.
At the same time, ADL 2026 compliance still relies heavily on fabric performance. New homes must meet three separate metrics: the Target Emission Rate (TER), the Target Primary Energy Rate (TPER) and the Target Fabric Energy Efficiency rate (TFEE).
Low-carbon technologies and renewables are the key to achieving the TER and TPER, but both remain strongly influenced by heat demand. Poor fabric performance increases heat demand and reduces the efficiency of technologies such as heat pumps. The result is that the fabric-first approach remains central to compliance.
Greater scrutiny
ADL 2026 also introduces far greater scrutiny of actual building performance.
The industry will transition from SAP 10.3 towards the Home Energy Model (HEM), which is intended to provide a more detailed assessment of operational energy use. While SAP remains in place for now, the direction of travel is clear: performance modelling will become more sophisticated and more closely tied to real building behaviour.
The updated guidance also increases reporting requirements. Signed BREL reports are now required at both design and as-built stages, alongside photographic evidence demonstrating that key construction details have been completed correctly on site.
This places far more emphasis on quality assurance during construction. Design-stage compliance alone is no longer enough. Project teams will need to demonstrate that specifications have been delivered accurately and consistently on site.
Homes are also encouraged to be “smart meter ready”, reflecting wider moves towards operational monitoring and energy flexibility.
Finer fabric margins
On paper, some fabric requirements appear relatively unchanged. Limiting U-values for many thermal elements are identical to those introduced under ADL 2021. In practice, however, the compliance margins are much tighter.
Window performance requirements have been strengthened, and thermal calculations must now account for a broader range of components and junctions. The guidance also makes clear that simply meeting limiting U-values may not be enough to satisfy the TFEE target.
That creates less tolerance for specification changes, poor detailing or inconsistent workmanship.
Cavity wall construction is a good example. A 100mm cavity wall may still achieve compliance in theory, but the overall specification quickly becomes restrictive. Triple glazing or reduced glazing areas may be needed to compensate, and exceptionally low airtightness cannot be used to mitigate a poorly performing fabric. Any substitution on site also carries more risk because there is less margin within the overall energy calculation.
As a result, many designers are likely to move towards more robust fabric specifications that provide greater flexibility and reduce compliance risk. Wider cavities and full-fill insulation systems can help improve thermal performance while simplifying installation and supporting airtightness targets.
Interactions with other regulations
ADL 2026 expands the number of what it describes as “key interactions” with other parts of the Building Regulations. This provides a useful starting point for understanding how compliance with Part L may be affected by wider regulatory obligations.
Fire safety is a good example. ADL 2026 highlights the need to consider fire performance due to the increased use of on-site electricity generation, particularly solar panels.
Fires associated with solar installations are a recognised risk and should be addressed during the design stage. The use of non-combustible insulation can help limit the spread of fire within the building fabric. Glass mineral wool, for example, is typically classified as A1 or A2-s1,d0 under the Euroclass reaction-to-fire system.
Fabric first for future homes
ADL 2026 raises expectations across the board. Heat pumps, solar generation and tighter reporting requirements may attract most attention, but the biggest shift is the reduced tolerance within the compliance process itself.
Fabric performance remains critical, but there is now far less room for error in design, specification or construction. For architects and specifiers, robust detailing and buildable fabric solutions will play a major role in delivering compliant homes consistently and efficiently.