ᐅ Roof Insulation for New Construction

Hello everyone,

In a quote for the roof structure of a new build, the carpenter is offering an underlay board (Gutex Multiplex, 35mm (1.4 inches)) even though insulation is planned for the drywall phase.

What do you think, is the underlay board additionally necessary? Are there any alternatives?

Thanks for your advice.

So, I assume this will be installed as a single-layer insulation above the rafters and then additional insulation between the rafters afterwards?
Whether this is necessary in terms of energy saving regulations or KfW classification, I cannot judge.
However, it can make sense, especially as protection against heat in summer. Additionally, it helps to avoid thermal bridges.
If the price is reasonable, it’s worth doing.
Alternatively, you can add a 4 cm (1.5 inch) insulation layer below the rafters as a DIY project with a similar effect.

The under-roof board would be installed as a continuous layer over the rafters.

As part of the drywall construction, insulation is planned to be installed between the rafters.

We are building a house following the energy-saving regulations without KfW funding.

The key factor is that the entire roof assembly functions properly. If several trades bring their own ideas to the table, it will end up going wrong, and you will have built a mold trap.

What is the SD value of the board?