Sheet or not? plastic or not?

[reineboy]

I will soon insulate a sloping roof (outer roof) and use raw cladding on the inside. What do you think, should I put some board (like OSB) behind, or do I just put a wind barrier behind?

The house was built in the 1920s, so there is natural ventilation. What do you think, should I have plastic in the walls or should we let it breathe a little?

Grateful for answers.

 

[frhe]

Only wind barrier.

Plastic or not depends on what you are insulating with. If, for example, fiberglass, you must use plastic. If cellulose, you can opt out and maybe choose a vapor-resistant wind fabric instead.

 

[gnilrub]

In what way does the type of insulation affect whether to use plastic or not? It sounds very strange to me. Putting OSB behind seems unnecessary. I insulated an old barn from the 1940s a while ago. We put paneling on the slanted roof and didn't have any board underneath. However, we did put plastic between the insulation and the paneling. There's a lot of talk nowadays about whether to use plastic on old houses, but I went with my gut feeling and felt that the plastic couldn't do any harm if you have a ventilated air gap on the outside.

 

[frhe]

In materials like fiberglass, moisture in the air will condense within the material, and therefore, the possibility of moisture entering it must be prevented. In, for instance, cellulose, a certain (quite large) amount of moisture can be absorbed by the material, which prevents condensation, allowing for the selection of a less dense material (provided that there are periods when the insulation is allowed to dry out).

You can also use plastic with cellulose, but for instance, in my case, it was completely impossible to achieve a completely covered wrapping, and to avoid moisture concentrating in the unwrapped areas, I chose to install a wind barrier instead (which is also quite vapor-tight).