New construction, insulation of the attic interior

Hi,

I am planning to insulate the attic myself in our new building.
Is there a tip for the insulation material?
The room should be used completely as a study,
I have already done some research on the internet and came across wood fiber insulation quite often and believe I have found the ideal solution here due to the low thermal conductivity.

Am I right or is there a better or equivalent but cheaper solution?

Thanks for your opinions!

One should use the insulation material specified in the energy certificate provided by the architect. At least the thickness and thermal conductivity stated there are decisive. Whether mineral wool or wood is used can be discussed afterwards.

I think I expressed myself incorrectly, sorry. The roof will be insulated normally to meet Kfw 40. I would add the additional insulation so that the attic can become a habitable room.

Be careful with the level of the vapor barrier. Simply applying interior insulation blindly can go wrong. Talk to the architect about what he recommends. And post the complete planned roof structure here.

I think I expressed myself incorrectly, sorry. The roof is insulated normally to meet KFW 40. I would add additional insulation so that the attic can become a habitable room.

Then I would omit the "additional" and include the roof in the thermal envelope right away. That way, it is done properly according to KfW 40.

Hi,

so, I have been expressing myself incorrectly the whole time.

I would do the insulation between the rafters of 240mm myself and am wavering between the building materials, it seems to me that wood fiber insulation is ideal here because of the heat protection, or am I wrong and is mineral wool etc. enough for the insulation between the rafters and wood fiber insulation as under-rafter insulation for heat protection?