FHS Fabric Specification Lookup
Use this free tool to look up the confirmed U-values and air permeability requirements for new dwellings under the Future Homes Standard. Select a building element to see the limiting and notional values.
For full details on Part L fabric changes, see our comprehensive guide to FHS Part L changes.
FHS Fabric Performance Values
Look up the fabric U-values and air permeability requirements for new dwellings under the Future Homes Standard. Backstop values (the absolute maximum permitted) are unchanged from Part L 2021. The two compliance routes (HEM and SAP 10.3) use different notional dwelling values, calibrated to achieve the same overall FHS performance standard. HEM notional values are from the consultation response (March 2026); the final dwelling notional buildings document has not yet been published. SAP 10.3 values are from Appendix R of the SAP 10.3 specification.
Select a building element above to see its performance requirements.