The Future Buildings Standard significantly raises the compliance bar for BRUKL reports. The tightened notional building specification means lower TER and TPER targets, requiring better fabric, low-carbon heating, solar PV, and efficient lighting to achieve compliance (AD L2 2026).
What has changed?
The core mechanism is the same – the actual building's BER and BPER are compared against targets derived from the notional building – but the notional building itself has been substantially upgraded.
| Aspect | Part L 2021 (NCM 2021) | FBS (2026 NCM not yet published) |
|---|---|---|
| Wall U-value (notional) | 0.18 / 0.26 W/m²K (side/top-lit) | TBC when 2026 NCM published |
| Roof U-value (notional) | 0.15 / 0.18 W/m²K (side/top-lit) | TBC when 2026 NCM published |
| Floor U-value (notional) | 0.15 / 0.22 W/m²K (side/top-lit) | TBC when 2026 NCM published |
| Window U-value (notional) | 1.4 W/m²K | TBC when 2026 NCM published |
| Air permeability (notional) | 3 / 5 m³/(h·m²) (side/top-lit) | TBC when 2026 NCM published |
| Heating system (notional) | Heat pump (side-lit) / direct electric (top-lit) | TBC when 2026 NCM published |
| Solar PV (notional) | 20% side-lit / 40% top-lit (NCM 2021, Equation 9) | 40% of foundation area (both zone types) - TBC when 2026 NCM published |
| Lighting efficacy (notional) | 105 lm/W | TBC when 2026 NCM published |
Part L 2021 column shows current NCM 2021 notional values. The 2026 NCM Modelling Guide has not yet been published; values in the FBS column will be confirmed when it is released.
Impact on assessors
For SBEM assessors producing BRUKL reports, the FBS changes mean:
- Updated software required – iSBEM and approved DSM tools will need to be updated to model the new notional building specification
- Design input earlier – the tighter targets mean energy strategy must be considered from the earliest design stages, not retrofitted at building control submission
- PV modelling – assessors will need to model solar PV as standard, including orientation, tilt, and capacity calculations
- Heat pump parameters – assessors will need accurate COP data for low-carbon heating systems, as these directly affect the compliance outcome
Impact by building type
Offices
Offices generally cope well with the FBS due to good roof area for PV and straightforward HVAC. The main challenge is meeting the overall compliance targets, which require strong performance across fabric, heating, and lighting.
Warehouses
Large roof areas make PV compliance straightforward. Heating requirements are often modest, and the switch to heat pump systems is less impactful for buildings with low heating demand.
Schools and healthcare
These building types face the greatest challenge due to complex ventilation requirements, high occupancy density, and often limited budgets. Early engagement with energy assessors is critical.
Retail
Small retail units may struggle with roof area for PV, while large retail formats generally cope. Refrigeration systems in food retail add complexity to the SBEM calculation.
Cost impact
The government's impact assessment estimates cost uplifts ranging from 0.6% for hospitals (£28/m²) to 2.6% for shallow-plan offices and hotels (£65/m² and £79/m² respectively) above Part L 2021 levels (FBS Impact Assessment, Table 16, p64). While upfront costs increase - primarily from PV installation, improved fabric, and low-carbon heating - the analysis shows a positive net present social value when operational savings and carbon reductions are factored in over the building's lifetime (FBS Impact Assessment, Table 16, p64).
Preparing for the change
Assessors and design teams should:
- Review the full notional building specification to understand the new targets
- Use the Compliance Route Finder to determine which standard applies to current projects
- Familiarise themselves with solar PV modelling in SBEM
- Check software updates – ensure iSBEM or DSM tools are updated for the 2026 notional building
Frequently Asked Questions
How has the FBS changed BRUKL compliance?
The FBS tightens the notional building specification, lowering the TER and TPER targets. Buildings now need better fabric (lower U-values), low-carbon heating, solar PV (40% of foundation area for both side-lit and top-lit), and 105 lm/W lighting to comply. The 2026 NCM has not yet been published.
Can a building with a gas boiler pass BRUKL under the FBS?
It is extremely difficult. The notional building assumes low-carbon heating, so a gas boiler creates a significant emissions penalty. Compliance would require exceptional performance in all other areas, which is rarely practical.