Calculations for all wall constructions: cavity walls, solid walls, timber frame, SIPs, ICF, steel frame and non-standard build-ups. Part L limiting value: 0.26 W/m²K.
Ground floor U-value calculations including perimeter/area ratio effects. Suspended floors, solid slabs, beam and block. Part L limiting value: 0.18 W/m²K.
Pitched roofs (between/over rafters), flat roofs (warm/cold deck), room-in-roof constructions. Part L limiting value: 0.16 W/m²K.
Window and door U-value calculations. Frame factors, glazing performance, overall Uw values. Part L limiting value: 1.6 W/m²K for windows.
Bespoke calculations for unusual constructions, heritage buildings, retrofit specifications and innovative building systems.
U-value calculations formatted for direct input into SAP assessments. Consistent methodology ensures accurate energy modelling.
| Element | Limiting U-Value | Typical Target |
|---|---|---|
| External Walls | 0.26 W/m²K | 0.18-0.22 W/m²K |
| Ground Floors | 0.18 W/m²K | 0.13-0.15 W/m²K |
| Roofs | 0.16 W/m²K | 0.11-0.13 W/m²K |
| Windows | 1.6 W/m²K | 1.2-1.4 W/m²K |
| Doors | 1.6 W/m²K | 1.0-1.4 W/m²K |
Note: Limiting values are maximums. Achieving TFEE compliance typically requires better performance.
A U-value measures how effective a building element is as an insulator. It represents the rate of heat transfer through a structure, measured in W/m²K (watts per square metre per degree Kelvin). Lower U-values indicate better insulation. Building Regulations set maximum U-values for walls, floors, roofs, windows and doors.
U-value calculations are required for Building Regulations compliance on new builds, extensions and renovations. They're needed for SAP calculations, to demonstrate Part L compliance, for planning applications involving energy performance, and when specifying non-standard construction build-ups.
Part L 2021 sets limiting U-values: Walls 0.26 W/m²K, Floors 0.18 W/m²K, Roofs 0.16 W/m²K, Windows/Doors 1.6 W/m²K. However, achieving the Target Fabric Energy Efficiency Standard (TFEE) often requires better performance than these limiting values.
U-values are calculated by analysing each layer of a construction element—materials, thicknesses, thermal conductivities—plus surface resistances and any air gaps. We use industry-standard methods (BR 443, BS EN ISO 6946) and software to produce accurate, compliant calculations.
We need detailed construction specifications: material types, thicknesses, densities where relevant, and the complete build-up from internal to external face. For windows and doors, we need frame types, glazing specifications and overall dimensions. Manufacturer data sheets are helpful.