The calculation for the insulation level of your house will be carried out by your architect. In order to obtain a construction licence, the calculation of the level and an affirmative form must be included with the application. Nevertheless, we would like to provide you with some basic definitions regarding insulation.
- λ-value
The main characteristic of a thermal insulating material is the “thermal conductivity coefficient” or λ-value (lambda-value) in terms of W/mK. The smaller the λ-value of a material, the less the heat will go through this material.
- R-value
The λ-value is a physical property of materials. However, in order to determine “the insulating quality” of a material with a certain thickness, we use the R-value or thermal resistance. The thermal resistance R of a material with a certain thickness d is calculated by dividing the thickness d (expressed in m) by the λ-value (R=d/λ expressed in m²K/W). The greater this R-value, the better the insulating capacity of the material. From this we can conclude that when using Unilin roof panels, you will obtain a greater R-value or better insulating capacity than from other insulation materials with the same insulation thickness.
- Rt-value
The total thermal resistance of a compound roof – for example a sandwich panel – is the sum of the thermal resistances of each material, to which we add the internal and external surface resistant coefficients.
Rt = R1+R2+R3+…
- U-value
The U-value or thermal transmission coefficient of a wall is calculated by taking the inversion of the Rt-value, or U=1/Rt expressed in W/m²K. The U-value reports how much warmth (W) goes through 1 m² roof between the inside and the outside per second and per degree difference in temperature (K). So the U-value is a property of a compound roof and not of a material. This is important as they talk in everyday language about a U-value of an insulation material, while this should be an R-value. This misconception has possibly something to do with the fact that in many constructions the R-value and therefore also the U-value is principally determined by the insulation layer.