ᐅ Insulating the Attic Floor

Hello everyone,

I would like to cover the attic floor (roof space) with OSB panels to make it fully walkable. Currently, only the wooden beams are visible. I plan to install glass wool insulation (friction-fit batts) between the rafters. Can I simply install the insulation like this, or do I need a vapor barrier as well? The roof is already insulated with wool and foil.

Thanks in advance for your help. I’m attaching a few pictures.

In my opinion, this can be done without a membrane. The building envelope and the transition between warm and cold areas is the insulation under the roof. Actually, the ceiling doesn’t necessarily need it. But it doesn’t do any harm either.

But the ceiling should be insulated. Well, not absolutely must, but it’s recommended. Otherwise, the attic will always be heated as well.
If you use wool insulation, please choose tongue-and-groove boards. They have more joints, allowing moisture to escape upwards.
Alternatively, make sure to leave plenty of gaps between OSB boards.
It is also important to install a basic form of forced ventilation if it’s not already in place. I assume the attic is not heated?

Yes, tongue and groove boarding. It also looks nicer.

Joedreck schrieb:

But the ceiling needs to be insulated. Well, what I mean is it should be. Otherwise, the attic will always be heated as well.
If you use mineral wool, please use tongue-and-groove boards. They have more joints, allowing moisture to escape upwards.
Alternatively, leave enough gaps between the OSB panels.
It is also important to install a basic form of forced ventilation if none is present. I assume the attic is not going to be heated?

That's correct; the attic will not be heated and will only be used for storage. What do you mean by forced ventilation? So, have I understood correctly that the vapor barrier foil is not necessary?

There is no insulation board under our tongue-and-groove boards either. The insulation wool is installed directly underneath. And all of this was done by a professional carpenter, a specialist. Not by me as an amateur. I only helped out and followed instructions. And in the end, I paid for it.