ᐅ Roof insulation between rafters – 200 or 220 mm

Created on: 27 Apr 2020 21:58
A
Appel2000
Good evening,

it's me again...
But I’m really impressed with the help here, no matter the topic.

One more question, this time about insulation between rafters:

- Rafters are 220mm (9 inches) thick
- Can / should / must I fill the entire rafter thickness?
- So, do I use 220mm (9 inches) insulation with a thermal conductivity of 0.035 W/(m·K)
- Or 200mm (8 inches) insulation with 0.032 W/(m·K) and leave 20mm (1 inch) of air space?

Thanks,
Regards and stay healthy!
A
Appel2000
4 May 2020 19:44
Of course, there is an underlayment membrane, the one at the roof/under the roof tiles. I hadn’t thought about that…

So, practically speaking: the roof is covered. We are doing the insulation between the rafters ourselves.

From the inside:
- drywall
- counter battens / laths
- vapor retarder
- insulation

That’s the end of our work; the rest is already “on the roof,” correct?