It's what is beneath what you see.människa said:
In Sweden, raw slats with surface felt are predominant (and ventilation beneath the raw slats). In the last 15-20 years, breathable membranes have become an alternative. Search for "diffusionsöppet undertak." Whether it works in your case, I won't say or promise.
glass/rock-wool breathes much more than cellulose. The strength of cellulose is that it can bind moisture so that it doesn't condense into water as easily.
But you are right, diffusion-open fabric over 200mm cellplast is of no use.
If you don't have special surface felt/membrane that is suited for construction without an air gap, then you should have an air gap. That is, if you have "regular" roofing felt, there should also be an air gap. Regardless of whether it's cellulose or another type of insulation. You could take a chance and it might work perfectly fine, but it feels unnecessary.
Thank you
After talking with the seller at our wood supplier, who is an old carpenter (old school, so I already knew what he would say
) it will be an air gap with a ventilated ridge. So now I'll let this go and move on
It was fun to follow your discussion
After talking with the seller at our wood supplier, who is an old carpenter (old school, so I already knew what he would say
) it will be an air gap with a ventilated ridge. So now I'll let this go and move on It was fun to follow your discussion