Insulate the roof: flakes, panels or wool

We are building with architects and single contracts. So far, it is going very well. The "absent-minded professor" is also bearable :)

It was actually a typo. Rafters will be 24 cm thick. Insulation between rafters is therefore also 24 cm. In terms of the roof structure, all three of the above-mentioned types of between-rafter insulation should be possible for us.

In my internet research, unfortunately, I could not find a good overview of the advantages and disadvantages of the different types of insulation and products. If anyone has a link for me, feel free to send it via PM.

What I have found out so far:

[*]The best price-performance ratio in terms of thermal protection is mineral wool.
[*]Only slightly worse thermal protection but significantly better summer insulation is offered by cellulose flakes, which are only marginally more expensive. However, I could not find any statements about shape stability and the risk of compression over the years. That would be my biggest concern with a gable roof.
[*]The most premium seem to be wood fiber boards, which besides acceptable thermal protection also provide good summer insulation and good sound insulation values. Among the three insulation types available, the boards are, however, the most expensive.

(The values naturally vary from product to product within the same insulation type in individual cases, of course. Here I am referring to rough and general approximate values.)

Is that correct so far?

Thank you very much for the advice.

We have blown in wood fiber insulation. According to our carpenter, there are regulations regarding the pressure/density with which the cavities are filled. Settling is supposed to be prevented by properly clean workmanship. When we observed the blowing process in practice, we had the impression that this is true. However, of course, we are only laypeople...

This is supposedly more difficult with stone wool, as perfect workmanship is more difficult and complex.

Expensive does not equal noble... :D

The cards are completely reshuffled when cables, lines (preferably already controlled residential ventilation here) run through the cavities. Then it gets pretty nasty with the "most noble" stuff. And mineral wool is no better there either.

Regarding the myth of sagging: I can show you pictures of component openings where cavities were insulated with mineral wool that has also sagged. :mad:

For blowing in: the whole thing is blown in under pressure so that it is evenly compacted. But this requires in the planning phase that the structural conditions are created and the cavities do not become too large. For example, I cannot fully fill a 7m long slope in one piece. So it depends on the planning and the person carrying it out. Although, if the drywall installer works like a wild boar by hand, then you can forget about it.
Conclusion: Mineral wool has the better thermal conductivity value, that's true. But for fairness, you have to consider it 40 to 40. And then mineral wool can never be cheaper than cellulose.

We did both - stone wool as 200 to 240 mm insulation between the rafters and then another 60 mm of wood fiber boards on top.

Wood fiber in this context is good for the ecological conscience and the wallet of the craftsmen. I would choose cellulose, but whether the heat protection is noticeably different with such a low thickness (except in your head), nobody can really prove that. You can search for a video on YouTube by Isover, where this topic is addressed.

And Isover wants an explanation for that :D?

The boards have a calculated summer thermal protection and you also save yourself a vulnerable USB, plus you have a rainproof emergency roof and a functioning vapor diffusion. Yes, more expensive, but combines many advantages - we were also able to save an intermediate batten insulation because we only have 20 mm rafters.