Insulation is not just insulation. It doesn't matter how thick the material is, but what's inside. You should pay attention to these key figures when making your selection.
Good insulation saves heating costs. But if you are looking for the right material for your house wall, the roof structure and the top floor ceiling, you can quickly be overwhelmed.
Who knows what polystyrene boards (EPS), mineral wool or polyurethane insulation boards offer? Whether extruded polystyrene (XPS) is better? Can natural insulating materials such as wood fibers, flax, hemp, cellulose, wool, straw, reed or cork actually keep up?
You should understand these three criteria as a guide:
Thermal conductivity - W/mK:
An important criterion is the thermal conductivity, also known as the U-value. Insulating materials with a thermal conductivity of between 0.03 and 0.05 watts per square meter and Kelvin (W/mK) are considered good facade insulation according to the Builder Protection Association (BSB). A thermal conductivity of less than 0.03 W/mK is very good.
Because: "The lower the thermal conductivity, i.e. the U-value, the better the material insulates," says BSB consultant Holger Schmidt. And then it can also be thinner than some other material with the same effect.
The consumer advice centers give examples: They want to bring a previously uninsulated wall with 1.2 W/mK to a U-value of 0.2 W/m2K. For this, a phenolic resin rigid foam must be less than ten centimeters thick, polyurethane ten centimeters and mineral wool 15 centimeters. Wood wool, hemp fibers and calcium silicate can be installed more than 15 centimeters thick, and cork even more than 20 centimeters thick. This can have decisive effects, for example, on property boundaries or in the case of interior insulation.
As with the facade, when insulating the roof, the thermal conductivity of the material is a major factor in determining how thick or thin the insulation can be. A material with an insulation value of 0.35 W/mK is the standard here, according to Michael Pannhausen, trainer at the DIY Academy in Cologne.
But there is one hurdle: "The thickness of the roof is determined by the height of the rafters between which the insulating material is laid," says Pannhausen. Since natural materials such as wood fiber usually achieve slightly worse values than 0.35 W/mK, they would have to be laid thicker and the rafters might have to be doubled.
For the basement ceiling, an insulation value of less than 0.2 watts per square meter and Kelvin is particularly good, according to the information program for the future of old buildings from the Baden-Württemberg Ministry of the Environment. This usually results in a thickness of at least twelve centimetres, for example if you insulate with polyurethane and at least 20 centimeters with soft wood fiber. This can become a hurdle if the ceiling height in the basement is very low.
Insulation effect - λ:
With this information one can also come across the value with the sign "λ". It stands for the Greek letter lambda - and when it comes to insulation, also for the insulating effect of a material. The same applies here: the smaller, the better. But in contrast to the U-value, this value is independent of the material thickness and therefore less meaningful in situations where room sizes are concerned.
Diffusion openness - μ:
Another value that renovators and builders should pay attention to when insulating is the diffusion openness of the insulating material. It provides information about how well the wall can still exchange air after insulation - i.e. how well it can "breathe". The value is indicated with "μ" and pronounced "mü".
The higher the value, the more airtight the insulating material is, explains Hans-Joachim Riechers, General Manager of the Association for Insulation Systems, Plaster and Mortar. Mineral wool boards achieve a value of 1 μ. The building material conducts water vapor just as well as air.
Soft wood fiber panels achieve a value between 5 and 10, polystyrene panels between 20 and 50. With a mineral exterior plaster, the μ value is around 10. For comparison: a plastic film has a μ value of 100,000.
(This article was first published on Wednesday, November 02, 2022.)
