Warehouse FBS Compliance

Warehouses see a modest cost uplift under the Future Buildings Standard. The preferred option adds £21/m² (1.1%) for distribution warehouses and £20/m² (1.1%) for retail warehouses (FBS Impact Assessment, Table 16, p64). These figures are well below the costs originally consulted on, primarily because the preferred option reduced PV from 75% to 40% and lowered lighting efficacy requirements for top-lit buildings (FBS Impact Assessment, Section 5). The remaining uplift is driven by the large roof area available for solar PV and the shift from gas-fired radiant heating to electric alternatives.

Top-lit vs side-lit: a critical distinction

The classification of a warehouse as top-lit or side-lit fundamentally determines its compliance pathway. The FBS impact assessment treats these as distinct archetypes with different heating strategies, PV requirements, and cost profiles (FBS Impact Assessment, Section 3):

• Top-lit warehouses – large single-volume spaces with rooflights providing primary daylighting from above. This includes most distribution warehouses, retail warehouses, and logistics centres. Top-lit spaces use electric radiant heating rather than heat pumps in the notional building specification.
• Side-lit warehouse areas – office wings, reception areas, and ancillary spaces within a warehouse complex that receive daylight from windows. These zones are treated as side-lit and follow the heat pump heating pathway.

Large roof PV opportunity

Warehouses present the greatest PV opportunity of any building type. Their large, flat or shallow-pitched roofs have minimal obstructions and can accommodate extensive solar arrays. The FBS policy requires PV equivalent to 40% of the building foundation area for all non-domestic buildings (consultation response, para 3.10, p18). The consultation originally proposed 75% for top-lit buildings under Option 1 (Do Maximum), but adopted 40% following industry feedback on cost and deliverability (consultation response, para 3.10, p18). For top-lit warehouses, both the FBS policy and the current NCM 2021 Equation 9 give the same 40% figure.

Key PV considerations for warehouses:

• Structural loading – lightweight portal frame roofs must be assessed for the additional dead load of PV panels, mounting systems, and ballast. Some existing structural designs may need strengthening, adding cost.
• Roof orientation and pitch – many warehouses use north-light or saw-tooth roof profiles for even daylighting. PV panels should be oriented to optimise generation, which may conflict with rooflight placement.
• Rooflight integration – top-lit warehouses depend on rooflights for daylight. Balancing PV coverage with adequate rooflight area is a design challenge. Excessive PV can reduce daylighting and increase artificial lighting demand, offsetting some generation benefit.
• Self-consumption vs export – distribution warehouses with high electricity demand (conveyor systems, charging, lighting) may consume a large proportion of PV generation on site, improving the economic case. Retail warehouses with lower electricity intensity may export more.

Heating strategy

The notional building specification diverges significantly between top-lit and side-lit spaces in its heating approach (FBS Impact Assessment, Section 6):

• Top-lit spaces: electric radiant heating – the notional building assumes electric radiant heating for top-lit warehouse spaces, not heat pumps. This reflects the practical difficulties of using wet heating systems in large-volume spaces where stratification makes warm-air or wet systems inefficient. Electric radiant heaters deliver heat directly to occupants and surfaces at floor level without heating the full air volume.
• Side-lit ancillary spaces: heat pumps – attached offices and welfare areas use heat pump heating consistent with the side-lit building specification. Air source heat pumps are the most common choice, with VRF systems an option for larger office wings.

For top-lit spaces, the practical heating options are:

• Electric radiant panels and tubes – ceiling or high-level mounted, providing targeted radiant heat to occupied zones. These are assumed 100% efficient in the energy model (AD L2 2026, Section on electric space heating).
• Electric warm air heaters – suitable for spaces requiring rapid warm-up, with timing and temperature demand control and zone controls for buildings over 150 m² (AD L2 2026, Section on electric space heating).
• Air source heat pumps with destratification – an alternative that can achieve higher seasonal efficiency than direct electric, but requires careful design to avoid heating the unoccupied upper volume of tall warehouse spaces.

Fabric and airtightness

Warehouse fabric performance is governed by the same limiting U-values as other non-domestic buildings (AD L2 2026, Table 3.1): roof 0.18 W/(m².K), wall 0.26 W/(m².K), floor 0.18 W/(m².K). For warehouses, the roof is the dominant thermal element given the high roof-to-floor-area ratio.

The FBS impact assessment specifically notes enhanced levels of airtightness for warehouses and sports halls, above 2021 Part L requirements (FBS Impact Assessment, Section 6). Key airtightness challenges include:

• Large doors – loading bay doors, roller shutters, and vehicle access doors (limiting U-value 1.3 W/(m².K) per AD L2 2026, Table 3.1) are major air leakage paths. High-speed automatic doors, air curtains, and dock-level shelters help reduce infiltration.
• Roof-to-wall junctions – the junction between profiled metal cladding panels and roof sheeting is a common leakage path, requiring continuous air barrier detailing.
• Service penetrations – high-level service entries, roof extract fans, and smoke ventilators all penetrate the building envelope and must be sealed effectively.

Cost impact

The FBS impact assessment models two warehouse archetypes under the preferred option (FBS Impact Assessment, Table 16, p64):

• Distribution warehouse: £21/m² additional cost, a 1.1% uplift on base build cost (FBS Impact Assessment, Table 16, p64)
• Retail warehouse: £20/m² additional cost, a 1.1% uplift on base build cost (FBS Impact Assessment, Table 16, p64)

These figures are significantly lower than the options originally consulted on, largely because the preferred option reduced PV from 75% to 40% and lowered lighting efficacy requirements for top-lit buildings (FBS Impact Assessment, Section 5). The primary cost drivers are:

• Solar PV installations on large roof areas – the single largest additional cost
• Transition from gas radiant heating to electric systems, including electrical infrastructure upgrades
• Enhanced airtightness detailing and testing
• Improved lighting controls (though the preferred option reduced lighting efficacy requirements for top-lit buildings)

Despite warehouses having the lowest base build cost per square metre of the modelled archetypes, the absolute additional cost remains modest at around £20 - £21/m². The impact assessment notes that buildings built to the FBS will be zero carbon ready, avoiding retrofit costs estimated at 66–80% more than building to the higher standard at the outset (FBS Impact Assessment, Section 2).

Practical tips for warehouse projects

• Classify zones early – confirm which areas are top-lit and which are side-lit at concept stage, as this determines the heating strategy and PV requirement for each zone
• Assess roof structural capacity – check whether the proposed portal frame or steel truss roof can support PV panel loads before committing to a PV layout
• Plan electrical infrastructure – the shift from gas heating to electric radiant systems and PV generation requires significantly more electrical capacity. Engage with the distribution network operator (DNO) early for connection and export agreements.
• Coordinate rooflights with PV – develop an integrated roof plan that optimises both daylighting and PV generation. Consider transparent PV panels over rooflight areas where technology permits.
• Detail the air barrier – given the enhanced airtightness requirement, invest in a detailed air barrier strategy with specified products and installation methods for every junction type
• Model heating zones carefully – in the SBEM assessment, ensure that heated and unheated warehouse zones are correctly defined, and that the electric radiant heating is modelled with appropriate controls