When people talk about insulation, they quickly talk about insulation values. Indeed, terms like the R-value you will come across when you start working with insulation materials.

But what exactly does this term mean? In this article, we would like to explain it to you in detail without falling into overly technical jargon.

The R-value stands for thermal resistance (R from Resistance in English) and indicates the thermal insulating capacity of a material layer, often used as an insulating value of double-glazed windows, walls, floors, roofs. The R value is the thermal resistance of a material layer and is expressed in m2K/W. The higher R, the greater the resistance that heat passes through and the better the material insulates. Or the less heat can be transported through a product, the higher the thermal resistance (R) of the product. Thermal resistance is thus a product property: it depends on the thickness (the thicker, the better) and on the λ-value or thermal conductivity (the lower, the better). 

Calculation of the R-value

The calculation of the R-value depends on the materials that make up the structure under investigation. The material thickness, in metres, is divided by the λ-value (the thermal conductivity). The higher the value, the better the insulation; a twice as thick layer also has proportionally twice as good thermal resistance.

The formula is R = d/λ where:

R = thermal resistance in m2 K/W
d = thickness of the material in m.
λ = thermal conductivity in W/m K

Example: An insulation material with a thickness of 16 cm (= 0.16 m) and an λ-value of 0.032 gives an R-value of 5m2K/W (0.16 / 0.032).

Most structures consist of more than 1 layer. The total R-value can be obtained by adding up the different thermal resistances of each layer.

Rtot = R1+R2+R3+R4

If a layer is heterogeneous (such as a truss structure with insulation or a timber frame wall), a specific calculation of the total R-value of the heterogeneous layer is needed.

Improve roof insulation value: good insulation is better

As a general rule, you can say that you can insulate quite well. Certainly don't be afraid to insulate because the extra investment in insulation material will quickly pay for itself. The cost per square metre usually drops the better you insulate because the energy performance increases significantly per cm of thickness. Especially in the long term, the better the insulation, the more beneficial it is for your home!

A term like the R-value is everyday stuff for an insulation specialist. Who can help you calculate the right insulation value and apply it professionally.