Insulation / Vapor Barrier Top Floor Ceiling / Collar Beam, Open Ceiling

Hello everyone,

I hope someone can help me. We bought a newly built semi-detached house and now have to insulate the top floor ceiling (wooden beams 20 cm). Unfortunately, I am an absolute novice, so my question is how the structure should be??

From below, drywall panels and in the bathroom the green Fermacell panels, so far so good, but how is it from above? The attic is not to be insulated and only accessible to the chimney sweep. In my opinion, I would now clamp 20 cm of glass wool between the beams and then put a vapor barrier foil on top of the beams and then panels to walk on again... is this the correct procedure and is the insulation sufficient? Please help!!! Thanks in advance

Exactly the opposite. Otherwise, you will have all the moisture in the insulation.

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Beam | Insulation | Beam
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Vapor barrier
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Drywall
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and important: if you lay boards in the attic, be sure to use tongue and groove boards and not OSB panels. Also leave some space at the edge. Otherwise, the insulation will eventually start to mold.

OK, that means viewed from below: vapor barrier foil on the beams, then drywall panels on top.... and from the attic floor: just the wool between the beams down to the vapor barrier foil and then boards on top, finished? Sorry if I misunderstood something... is 20 cm of insulation enough? And what about the attic stairs? Do I have to consider anything there and do I just take one that is well insulated like the one from Wellhöfer??

Honestly? Get a professional. This is such a critical spot on a cold roof, especially when the staircase still has to be installed, a layperson should stay away from it. We have a Kfw55 attic staircase installed and are glad that someone else has to take the warranty to ensure that nothing goes wrong.

In this context, a question right away: The OSB boards act like an additional vapor barrier. Is there actually a difference between sanded and unsanded?