Kingspan U-Value Calculator
Estimate thermal transmittance (U-value), total thermal resistance (R-value), and heat loss for a basic build-up.
Optional Additional Layers
Surface Resistances & Heat Loss
What this Kingspan U-value calculator does
This tool helps you estimate the U-value (W/m²K) of a wall, roof, or floor construction using Kingspan insulation and optional extra layers. It also gives a quick heat-loss estimate based on area and temperature difference.
Lower U-values mean better thermal performance. In practical terms, a lower U-value usually means less heating demand and better comfort.
How U-values are calculated
The calculator uses the standard method:
- R-value of each layer = thickness (m) ÷ thermal conductivity λ (W/m·K)
- Total R-value = Rsi + Rse + sum of all layer R-values
- U-value = 1 ÷ total R-value
It then estimates steady-state heat loss:
- Heat loss (W) = U × Area × ΔT
Typical Kingspan lambda values
Always check the exact product datasheet. Lambda values vary by board type and facing.
| Product (example) | Typical λ (W/m·K) | Use case |
|---|---|---|
| Kooltherm K8 | 0.018 | High-performance cavity wall insulation |
| Kooltherm K7 | 0.020 | Pitched roof / wall applications |
| Kooltherm K3 / K5 | 0.021 | Floor / external wall insulation |
| Thermawall TW50 / TP10 | 0.022 | Wall and roof PIR insulation |
| Generic PIR board | 0.026 | Budget or older PIR assumptions |
How to use this calculator effectively
1) Select a product preset or enter custom lambda
If you know the exact product, use its declared λ from the latest technical sheet. Presets are only quick references.
2) Enter insulation thickness in millimeters
Common thicknesses are 50 mm, 75 mm, 100 mm, and 120 mm. Greater thickness generally improves thermal performance.
3) Add other layers if needed
You can include internal board, masonry, or other homogeneous layers. Enter thickness and λ for each one.
4) Check heat loss for a real area
Input area and temperature difference to estimate heat flow through that element. This helps with quick option comparisons.
Interpreting your result
- U ≤ 0.15 W/m²K: very strong thermal performance (common for efficient roofs/walls)
- 0.16 to 0.26 W/m²K: generally good performance for many modern applications
- > 0.26 W/m²K: can often be improved by increasing insulation thickness or choosing lower λ insulation
Example scenario
Suppose you enter:
- Kingspan thickness: 100 mm
- Kingspan λ: 0.022 W/m·K
- Plasterboard layer: 12.5 mm at 0.25 W/m·K
- Block layer: 100 mm at 0.77 W/m·K
- Rsi = 0.13, Rse = 0.04
The calculator combines all layer resistances and gives a resulting U-value. Try increasing Kingspan thickness to 120 mm to see how quickly U-value drops.
Ways to improve U-value
- Increase insulation thickness where practical.
- Use a lower-λ board when space is limited.
- Reduce thermal bridging at studs, fixings, and junctions.
- Check air-tightness and continuity of insulation.
- Validate with full construction details before procurement.
Important limitations
This calculator assumes ideal, one-dimensional heat flow through homogeneous layers. Real buildings include repeating thermal bridges (studs/joists), junction losses, cavity effects, and workmanship factors. Use this tool for planning and comparison, not final regulatory sign-off.