Roof insulation polyurethane PU rigid foam 100mm thick

Dear Anke, if you were a roofer and wanted to cheat the customer, would you say: Dear customer, go to the carpenter and order [Klemmfilz] between the rafters?

Hello Nordlys, well I don't think I would say it like that... As a nurse, I also don't say, take this pill and you will be completely healthy again. But yes, of course, you are right... many craftsmen only see the "quick" money.

find someone who takes the topic as seriously as you do. Possibly through an architect and then give the craftsmen very concrete specifications. This also makes it easier to compare offers. An acquaintance is now renovating his old building and they are laying 14 or 16cm of mineral wool between the rafters. In addition, there is continuous insulation with wood fiber as heat protection. That was the architect's suggestion; the craftsmen had other ideas.

10cm of lightweight expensive material is simply not enough. The money is better invested in insulation thickness and mass. If you’re already reroofing, do it properly. Did you read the note about the U-value calculator and phase shift?

Heat protection: it also depends on the conditions what is necessary. We manage very well with "only" 20cm of mineral wool insulation between rafters, but thanks to a third gable facing south, we have only a little unprotected roof area behind the living spaces (max 26°) and the attic is insulated (up to about 30°) but uninhabited. Soundproofing is not good but doesn’t matter for us.

Hello ,
Thank you very much for your post!!!
Yes, you are right... I will contact an architect. You spend (very very very) much money on the roof, and it should be good afterwards.
The idea of using wood fibers as counter battens and wool as insulation between joists is also my consideration. As already mentioned (and by you too), the craftsmen absolutely do not offer that.
Yes, I have read about the phase shift... but I'm sorry, I don't understand the calculator. I have to look at it again in peace.
Nice that you are satisfied with your roof!!! Many thanks to everyone who is actively sharing "their two cents" here... Although the topic (at the beginning) was so boring, I find it more and more exciting.
Thanks to everyone!!!! Gladly more... further experience reports.

Yes, I have read about the phase shift... but I'm sorry, I don't understand the calculator.

With 10cm of light insulation like mineral wool or your 023 PUR, the heat theoretically passes through to the inside after 3-4 hours. With 20cm, it takes 5-6 hours. Ideally, it should be 10-12 hours because then the heat is released outward overnight instead of inward. This is not achievable with exclusively light insulation materials; heavier and somewhat less insulating materials are needed for that. With the calculator you can, among other things, determine this value to roughly assess proposals for roof constructions yourself. Now you know about the 10cm.

Yes, I have the PUR insulation and yes, it is only 5cm mineral wool. The total insulation is, I believe, 20cm if I am not mistaken. As I wrote, I am (very) satisfied with the heat protection. I also do not have insulation between the rafters because I have an exposed roof truss. According to my research, I can only say that PUR is not the right choice for intentional good sound insulation. There are better options for that. However, one must not forget that sound can also enter the apartment through other means, especially in old buildings where not everything is perfect or can be made perfect. To summarize what has been written in this thread: PUR = good and inexpensive, but there are better options, especially for sound and heat protection.