Roof insulation new construction

Hello everyone,

for an offer on the roof structure in the new construction, the carpenter is offering an underlayment board (Gutex Multiplex, 35mm), although insulation is planned during the drywall construction.

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

Thanks for your advice.

So I assume that this will be installed as rafter insulation and afterwards also as intermediate rafter insulation? I cannot assess whether this is necessary in terms of the energy saving ordinance or KFW classification. However, it can make sense, especially in summer, as heat protection. Furthermore, thermal bridges are avoided. At a good, acceptable price, it can be done. Likewise, as DIY work, an additional 4 cm insulation layer can be installed under the rafters with a similar effect.

The underroof panel would be installed as a rafter overlay.

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

We are building a house according to the [Energieeinsparverordnung] without [KfW] funding.

The crucial thing is that the entire roof structure is functional. If several trades bring in their own ideas there, it will go wrong afterwards and you will have built a mold castle.

What is the SD value of the board?