Is wood fiberboard necessary under the roof?

the underlay membrane can then be omitted. Doing it twice makes no sense

the underlayment membrane can then be omitted. Doing it twice makes no sense

The underlayment membrane would also be omitted if one decides on the wood fiber boards.

In case of tile damage, there is the underlay membrane, not an additional insulation. But for 4000€ I can think of something much better. The benefit approaches zero.

Yes, I basically see it the same way. A roof insulation gives me no advantage compared to insulation on the top floor ceiling. Especially since roof insulation is also more expensive. The question is whether we should use wood fiber boards instead of the underlay membrane. But I also suspect that the extra cost is not worth it.

Well, you do have the advantage of being able to store temperature-sensitive items there. Whether it is worth the additional cost is something one has to consider.

Well, you do have the advantage of being able to store temperature-sensitive items there. Whether the extra cost is worth it is something you have to consider.

Yeah, that's true, you do have that advantage. But since we have a basement, we actually plan to store as little as possible there (actually nothing that is going to be touched in the next few years). I think it doesn't make sense for us directly.

In this case, I would decide the same way.