ᐅ Omitting the Vapor Retarder with Wood Fiber Insulation

Hi.

I took the construction example from the Steico manual. It uses a vapor retarder on the inside. See the picture. The plan is to use a combination of exterior and cavity insulation with wood fiber.

Steico, for example, recommends the following vapor retarders

I am reluctant to install a plastic sheet on the inside when using an ecological material like wood. We try to avoid plastics as much as possible.

Are there alternatives? I have read that with OSB4 boards, it is sometimes possible to skip the vapor retarder. Steico also mentioned in renovation reports that they only installed an airtight membrane between the exterior and cavity insulation.

Ideally, I would like to install an OSB board below the rafters and then a gypsum plasterboard. If you want to attach something to the sloped ceiling, the screws would hold in the OSB board at the latest. Unlike membranes, I don’t believe that tongue-and-groove OSB boards can be installed completely airtight. What happens if I screw through and later remove the screw? Then there would be a filled "hole" in the OSB board.

Thanks.
Best regards

OSB is also made using adhesives.
So, if you prioritize building in a health-conscious way, I would recommend checking out Baufritz.
They invest huge amounts in researching modern, bio-certified, sustainable building materials.
If it were possible without a barrier layer, they would do it 😉