What vapor barrier option to choose for the roof?
We would like to build a wooden frame house in a vapor permeable construction. Now we have a proposal with different options for roof construction or vapor barrier performance. Can anyone here give an assessment of the advantages/disadvantages?
-roofing shingles.
-8 cm purlins / counter purlins
-7 cm soft fibreboards
— 20 cm rafters with wood-fiber insulation
-foil insulation
-grids / counter grids
-gypsum board
-wallpaper/plasterboard
This is a construction in an occupied attic. In the attic, OSB is used as a vapor barrier for the brake itself, stiffening and sheathing.
As an alternative for the residential attic, I have been offered a heavy paper/cardboard vapor barrier with fabric (Pro Clima) or OSB boards. What should I think of this?
Answers
Drywall also needs to be treated. It's not as labor intensive, but it is. And the foil is relatively error-resistant.
Then the OSB boards must be tongue and groove glued accordingly, and the joint with the wall must be secured with permanently elastic strips.
Both options have their advantages and disadvantages. I would choose OSB.
The vapor barrier must prevent moisture from getting from the living space into the insulation so that it does not get moldy
Is an OSB board a substitute for vapor barrier? I've never heard and have a hard time believing that OSB is inherently vapor-proof, but I'm willing to prove that it isn't.
There is a difference between a vapor barrier and a vapor barrier.
There is also summer (warm outside = warm insulation) and winter (cold outside = cold insulation).
If steam goes from the inside (quite warm) to the insulation (if warm), not much happens, the steam passes through the insulation to the outside and the insulation dries out.
If steam from inside (quite warm) reaches the insulation (when cold), the steam condenses and the insulation becomes damp/wet and can't dry out because of the cold. Mold can form.
A "climate membrane" seems like the perfect hero. When it's warm outside, it's "automatically" open to diffusion (more like a vapor barrier). When it's cold outside, the membrane makes you (barrier). Overall, there is less risk of mold (at least theoretically).
A vapor barrier is only necessary where steam is generated (people) and insulation protection is needed.
OSB as an attic floor has no effect because it is installed over the insulation.
I've lined a kitchen island with OSB myself, and I can tell you that there's quite a bit of work to be done before you glue it with painter's fleece.
Foil is much less prone to mistakes when doing it. If there is a hole in it, you will see it. At first glance, the tightness of the tongue-and-groove joint is not in doubt, but at second glance it is not, because tongue and groove are not always treated equally well or damaged in transit. Then you come to the conclusion that a leak in the joint can only be detected with a BD test or similar instrument. In addition, wall connections with so-called "permanently elastic joints" are guaranteed to be more prone to defects than plastered film and, above all, less durable.
So instead of foil, battens and drywall, we just screwed OSB to it and glued tongue and groove.
We put diffusion tape on the joints if necessary. It looks neat and does less work and less height.
I wouldn't trust OSB as a vapor barrier in a living space. Also, the surface needs to be treated until wallpaper can be put on it. I would also prefer foil over paper, paper would probably deteriorate immediately in the event of a little water damage, right?
