Typical UK Building Regulations target U-values (for reference only):
- Walls: 0.18 - 0.30 W/m²K
- Roofs: 0.11 - 0.20 W/m²K
- Floors: 0.18 - 0.25 W/m²K
Note: These are typical values. Always check current regulations and project-specific requirements.
Step-by-Step Breakdown
| Layer | Thickness (mm) | λ (W/m·K) | R-value (m²K/W) |
|---|---|---|---|
| Total Thermal Resistance (ΣR): | 0.000 m²K/W | ||
| U-Value (1/ΣR): | 0.000 W/m²K | ||
A U-value measures how much heat passes through a building element (wall, roof, floor, etc.). It's expressed in W/m²K (Watts per square metre per Kelvin).
Lower U-values = better insulation. A well-insulated wall might have a U-value of 0.18 W/m²K, while a poorly insulated one could be 1.5 W/m²K or higher.
U-values are critical for:
- Meeting UK Building Regulations
- Reducing heating costs and energy consumption
- Improving comfort and reducing condensation risk
- Achieving sustainability certifications (BREEAM, Passivhaus, etc.)
The U-value is calculated using thermal resistance (R-value) for each layer:
- Calculate R-value for each layer: R = thickness (m) ÷ lambda (λ)
- Add surface resistances: Rsi (internal) and Rse (external)
- Sum all resistances: ΣR = Rsi + R₁ + R₂ + ... + Rse
- Calculate U-value: U = 1 ÷ ΣR
Lambda (λ) is the thermal conductivity of each material—a property that describes how easily heat flows through it.
Yes! This calculator supports unlimited layers. Simply click "+ Add Layer" to add more materials to your construction.
Build up your construction from outside to inside, including:
- External finishes (brick, render, cladding)
- Insulation layers (PIR/PUR boards, mineral wool, etc.)
- Structural elements (blockwork, timber, concrete)
- Cavities and air gaps
- Internal finishes (plasterboard, plaster)
You can reorder or remove layers as needed.
UK Building Regulations specify maximum U-values for new builds and renovations. Typical targets include:
- External Walls: 0.18 - 0.30 W/m²K
- Roofs: 0.11 - 0.20 W/m²K
- Floors: 0.18 - 0.25 W/m²K
- Windows/Doors: 1.4 - 1.6 W/m²K
Important: These are general guidelines. Always consult the current Building Regulations for your specific project, location (England, Wales, Scotland, Northern Ireland), and building type. Higher-performance standards like Passivhaus require much lower U-values (often < 0.15 W/m²K).