The U-value denotes the so-called heat transfer coefficient "U" in W/m²K. This value indicates the heat output through 1m² of the respective component, provided the difference in temperature between the two sides is 1 K. The calculation is made using the thermal conductivity (λ) of the building material in W/mK and the thickness of the material.
Calculator
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Use calculator:
- Enter the thermal conductivity ("Î") in W/mK.
- Enter the thickness of the building material.
- Click on "generate" to get the result.
U-value formula
U-value: ((W/mK) / thickness of the component) * 100
table
| Building material | Thermal conductivity (λ) |
|---|---|
| Concrete | 2.1 W/mK |
| glass | 0.76 W/mK |
| Granite | 2.8 W/mK |
| Wood | 0.19 W/mK |
| Limestone | 2.2 W/mK |
| Marble | 2.8 W/mK |
| Sandstone | 2.3 W/mK |
| steel | 48 W/mK |
First of all, you need to know the different thermal conductivities of the building materials in your building. These can be found in a table that you can obtain from the housing inspection office. You can then use these values to determine the so-called total U-values, which represent the total of all heat transfer coefficients of the building.
Next, you need to calculate the volume of the building by multiplying the floor area by the height. This gives you the total volume of the building in cubic meters.
You then need to calculate the U-value using the total U-values and the volume. To do this, first calculate the quotient of the total U-values and the volume and multiply this by 1000. The resulting value is the U-value of the building in watts per square meter Kelvin (W/m²K).
To determine the U-value even more precisely, you should also take into account the thickness of each individual layer. To do this, add up all the thicknesses of the individual layers and divide this by the volume of the building. This gives you the mass per cubic meter (kg/m³). The last step is to calculate the quotient of the U-value and the mass per cubic meter. The resulting value is the final U-value of your building in watts per meter Kelvin (W/mK).