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

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

Sanded or unsanded is just an optical thing. However, there are OSB boards in different types (1, 2, 3, and 4). OSB 3 and 4 can be used as vapor barriers, OSB 4 is additionally suitable for wet rooms.

Regards

Hi, if you have bought a new building, you have also received a heat demand calculation. It lists all the components and how they need to be insulated. And which WLGs. If you really have no idea at all, it will not be easy to make the vapor barrier 100% airtight. Seals, connections to the wall/floor, etc. The construction from below is gypsum board (in the bathroom green, Fermacell does not have green boards, there you can screw on the same board everywhere, but with a 5mm gap) then sheathing (preferably 23x72mm raw, dry) vapor barrier (please not the cheapest plastic foil (blue, blue-white...) there are better products, Isover, Würth db2...) and then your insulation in the cavities. Best solution 20cm compression felt WLG035, raw dry battens crosswise on the collar beams and then another 60mm mats 0.35 in there, then tongue and groove raw, dry. Then you have 26cm insulation and your wallet will thank you quickly.

...Then you have 26cm of insulation and your wallet will thank you quickly.

not entirely, because from an economic perspective, there is a component-specific, optimal insulation. If the OGD, for example, only accounts for 5% of the total transmission heat losses, "excessive" insulation measures hardly pay off economically. Another aspect comes into play, the heat generator! If it is, for example, a heat pump, the economic leverage effect of an insulation measure looks completely different than if, for example, a heat generator operates based on combustion principles.

best regards