ᐅ Roof insulation made of 100mm thick rigid polyurethane (PU) foam

Hello everyone,
I urgently need some advice and tips regarding roof insulation.
We plan to have our roof replaced next year. Now, the topic is roof insulation. Our roofer recommended the following:
Polyurethane (PU) rigid foam, 100mm (4 inches) thick // Type: puren Protect N 023.
This would be an insulation installed above the rafters (i.e., external insulation). However, I have read in forums and other sources that sound insulation with this type of material often falls short. The noise level can sometimes be quite high. This is partly due to the boards themselves (as they apparently expand and contract, especially at night) and also because the boards do not provide good soundproofing.
We would really like the space under the roof to be more comfortable in summer and, of course, quieter—or at least that outside noise levels are bearable.
Can you give us advice on the best way to insulate a roof like this? Has anyone had experience with this type: puren Protect N 023?
Please help... THANK YOU!!!
Best regards, Anke

I think that using cavity insulation between rafters with flexible insulation batts would provide better soundproofing, but the efficiency of the polyurethane boards installed on the rafters is higher.

Hello Nordlys,
Thank you for your post.
So, in our case, would you recommend installing these PU boards and additionally adding this insulation between the rafters for soundproofing? I’m quite unsure now. You spend a lot of money and want it to be done well in the end. Many people complain about these PU boards...
- In summer, it would still be very hot, and on top of that, the soundproofing is really poor.

I see companies here building new houses with an intended living space in the attic. They use insulation between the rafters and under-rafter insulation with glass wool. K.

Insulation below the rafters? So, probably not the insulation above the rafters then???

This is how they do it in new constructions here. Team Massiv, Specht, ECO, and others.
I’m not a carpenter, I just see what I see, and they have cavity insulation between the rafters, which keeps it quite quiet up there. However, our attic is used as a basement, not as living space. It also stays relatively cool in the summer. Relatively, that is—not like downstairs.