Notional isn’t necessarily optimal Although the new Approved Document L outlines the importance of the notional dwelling, following this is only one path to compliance. In practice, the notional dwelling can be restrictive, and specifiers should look for the optimal approach, considering the whole fabric and other performance factors. Specifiers must hit the TFEE, but how the building achieves that is flexible and should be considered on a case-by-case basis As-built performance A significant change within the new standard is the emphasis on demonstrating performance in the completed building. The shift towards as-built verification was introduced in the 2021 Part L update through the BREL report. This must be completed at both the design stage and after construction, placing greater importance on ensuring that what is built aligns with what was specified. Looking ahead, the Home Energy Model (HEM) will replace SAP 10.3 as the primary calculation methodology. This will allow for a more detailed and dynamic assessment of building performance, helping to bring predicted and actual outcomes closer together. Deeper lofts, wider walls For many house types, improving fabric performance will come down to increasing insulation levels and adjusting construction details. Deeper loft insulation and wider wall cavities are likely to become more common approaches. Loft insulation has long been recognised as an effective and
economical way to improve overall performance. Depths of up to 500mm are now regularly specified and should be considered when designing to meet future requirements. Wider wall cavities are also becoming more prevalent. A survey
conducted in late 2025 of Professional Builder readers found that 77% of respondents who build with masonry cavity walls plan to use 150mm cavities when the Future Homes Standard comes into effect, with a further 23% considering it. Beyond lambda Fabric specification involves more than selecting insulation based on lambda values. Airtightness and the control of thermal bridging are critical factors in meeting the requirements of Approved Document L. To minimise thermal bridging, details need to avoid complexity where possible, and it’s recommended to pick them from a database of independently assessed details. Material choice can also contribute to performance on site.
Flexible or loose-fill insulants, such as glass mineral wool, can support thermal continuity and help achieve a consistent fit around more complex details. Fire safety should also be considered. Fires associated with solar panels are a recognised risk and should be accounted for in the design. The use of non-combustible insulation can help limit the spread of fire within the building fabric. Glass mineral wool is typically classified as A1 or A2-s1,d0 under the Euroclass reaction to fire system, although ratings can vary between products. Specifying fabric for future homes Unpacking the Future Homes Standard underlines the central role of the building fabric in delivering future homes. It influences energy demand, supports the performance of low-carbon systems and determines whether targets are achieved in practice. Specification, buildability and attention to detail will ultimately decide outcomes on site. Prioritising robust, practical fabric solutions from the outset will be essential to closing the performance gap and ensuring homes perform as intended.
KA201
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51
