Insulation & Environmental
Calculators

Why Accurate Insulation Calculations Matter

Meeting Building Regulations Part L thermal performance requirements starts with getting the insulation specification right. Too little insulation fails the U-value target; too much is waste of budget. The right thickness depends on the product's thermal conductivity (lambda value), the target U-value, and any thermal bridging through fixings or structure.

Our insulation and environmental calculators help you arrive at the right quantities and system sizes quickly. Whether you are specifying rigid board insulation for a floor, calculating damp proof membrane for a basement conversion, or sizing a soakaway system for planning approval, these tools give you a reliable starting point.

Always verify final specifications with a building surveyor or structural engineer where compliance with Building Regulations is required.

Key Factors in Insulation Calculations

• Lambda value drives thicknessThe lower the lambda value (W/mK) of an insulation product, the thinner the board you need to achieve the same U-value. EPS is around 0.038, PIR around 0.022, phenolic around 0.018.
• U-value targets vary by elementBuilding Regulations Part L sets different U-value targets for floors, walls, and roofs. For new build, floors typically target 0.13-0.15 W/m2K, walls 0.18-0.26, and roofs 0.13-0.18.
• DPM laps must be sealedAll laps in damp proof membrane must be a minimum of 150mm and sealed with the manufacturer's recommended tape to maintain continuity of the barrier.
• Attenuation tank sizingAttenuation tank volume is calculated from the impermeable drainage area, the design storm event (typically 1:30 year for simple greenfield runoff rates), and the permitted discharge rate.
• Thermal bridging adds upMechanical fixings, wall ties, and structural elements that bridge the insulation layer increase the effective U-value through psi-value thermal bridging. This must be accounted for in SAP calculations.