U-Value Calculator
Accurately calculating U-values is essential to understanding how well roofs, walls, or floors retain heat. The IKO U-value calculator helps specifiers, contractors, and consultants determine the thermal transmittance of their proposed roof build-up, wall cavities, or floors, supporting energy efficiency, regulation compliance, and effective insulation specification. Whether you’re working on a school, hospital, government building refurbishment, or residential project, this tool allows you to model your build and explore insulation thickness options, quickly and reliably.
Why use our U-value calculator?
A U-value measures heat transfer through the roof, walls, or floors, expressed in W/m²K. The lower the U-value, the better the construction resists heat loss.
It’s especially useful at early design and tender stages, helping you reduce risk, optimise material selection, and meet performance targets confidently.
This tool helps you:
- Estimate thermal performance across a full roof build-up, walls, or floors.
- Test insulation thicknesses and material combinations.
- Understand the impact of air gaps, vapour control layers, and thermal resistance.
- Compare options in line with Part L1 and Section 6 Scottish Building Regulation requirements or project-specific performance goals.
How to calculate a U-value:
U-value is calculated by assessing the thermal conductivity (λ-value) and thickness of each material layer in the system, including insulation, membranes, and air gaps.
The U-value calculator does this automatically, and the result gives a realistic view of the system’s ability to resist heat loss, which is vital for long-term energy efficiency.
How the calculator works:
- Assigns thermal resistance (R-values) to each layer.
- Accounts for any internal or external resistances.
- Sums total thermal resistance to output thermal transmittance (U-value).
How to calculate the U-value:
To get started, input your proposed roof build-up using selections for:
- Construction type (e.g. pitched or flat roof, floors, or walls).
- Material details and outline build-ups.
- Vapour control layer.
- Insulation type and thickness.
- Target U-value.
The calculator will provide:
- Total U-value (W/m²K).
- An indicative build-up with insulation calculation.
- Recommendations or adjustments to achieve compliance.
Where this tool applies:
IKO’s U-value calculator supports energy-efficient build-ups across a wide range of sectors, including:
- Education – new schools and CIF-funded upgrades.
- Healthcare – NHS and private hospital roofs with strict energy performance targets.
- Government & civic buildings – compliance with public procurement and Net Zero goals.
- Commercial refurbishment – upgrading ageing stock to modern thermal standards.
- Residential – new, refurbishment, and extensions.
Need technical support?
IKO’s Technical Team can help interpret your results or provide full build-up guidance, including condensation risk analysis for flat roof and tapered insulation designs and full U-value reporting for submission.