Wood fiber, mineral wool, or Styrofoam insulation

Hello forum,


We are renovating a semi-detached house built in 1963 and want to achieve KFW70EE. For this, we need a U-value below 0.14 W/m2K.

For this, the roof must be renovated and newly covered. We have spoken to a few roofers and obtained quotes.

There are significant differences in the offers, depending on the insulation. The cheapest is 160 mm PUREN continuous insulation or comparable.

While some roofers swear by it, others advise against it. The supporters cite good insulation properties and easy handling. The opponents of polystyrene cite poor heat protection and poor sound insulation. Environmental friendliness is also criticized.
Now I have modeled the insulation once with the U-value calculator. My original goal was to experiment with which insulation combinations produce the best values for cold and heat protection. Because especially the poor heat protection was a thorn in my side, since an office is to be created under the roof.

Quite by chance, I then came across the fact that a continuous insulation with 160 mm Puren also has good heat protection if a still air layer is inserted between the rafters and 2 layers of gypsum board are installed underneath.

This construction would pretty much refute the argument of poor heat protection, and I actually like the insulation setup quite a bit. It is also much cheaper than wood fiber insulation, which is known for better heat protection.

Have I forgotten something?

We had a semi-detached house, I would design the insulation more for cold and noise. In summer, with 35 degrees during the day and 28 at night, it gets really warm upstairs after three days, despite shading. We always dreamed of a [Klima-Split], but never installed one.

Puren is not Styrofoam.

It would be even better if you combine Puren instead of an air layer with an intermediate insulation with high density, such as wood fiber. Then you have the perfect combination when it comes to heat (and especially also sound insulation). Perhaps this can optimize the total thicknesses so that the (additional) costs can be kept correspondingly low.

However, the vapor barrier must then be glued very carefully.

Puren (by the way, that's just the manufacturer) - that is a PU insulation. The most expensive material (except for Resol and vacuum insulation panels) you can get, but by far (excluding the aforementioned materials) the most effective insulation. It has a U-value of 023 in the aluminum-coated version that you were offered. The 160mm corresponds in insulating effect to about 245mm of mineral wool with a U-value of 035. With that, you are already at KfW 55, right? I would calmly build the roof as you planned.