U-value calculator
A U-value measures how effective a building element (like a wall, roof, or window) is as an insulator. It represents the rate of heat transfer through one square metre of the element for every degree of temperature difference between the inside and outside.
The lower the U-value, the better the insulation.
Why U-values matter
Understanding U-values helps you:
- Compare materials: See the difference between 100mm and 200mm of insulation.
- Calculate savings: Estimate how much heat you will stop from escaping.
- Check compliance: Ensure your renovations meet the UK Building Regulations (Part L).
Target U-values (UK Building Regs)
| Element | Target U-value (W/m²K) |
|---|---|
| New Roof | 0.15 |
| New Wall | 0.18 |
| New Floor | 0.18 |
| New Window | 1.40 |
How to use the calculator
To estimate the U-value of your wall or roof, you will need to know:
- The thickness of each layer (e.g., 100mm of brick, 50mm of air, 100mm of block).
- The material type of each layer (to determine its thermal conductivity or R-value).
Calculation formula: The U-value is the inverse of the sum of all the thermal resistances (R-values) of the layers: U = 1 / (R1 + R2 + R3 + …)
Interactive Calculator
Layers (from outside to inside)
While this tool provides a good estimate, for official purposes (such as building control or grant applications), a qualified surveyor or architect should perform a formal U-value calculation using specialized software.