ᐅ Is it possible to construct a roof without using a membrane?

Hello,

Since I really dislike using membranes, I would prefer to avoid them in my new build. For insulation, I am considering wood fiber boards like Steicoflex, followed by a water-repellent layer such as Steico Universal Dry. Now, my questions:

Is it true that glued OSB boards on the interior side are sufficient as a vapor retarder?
Would it make sense to add another traditional layer of boards and roofing felt beneath the tiles, on top of the Universal Dry layer, with proper ventilation of course?
I am planning to build a roof with a moderate pitch, and here in the Pre-Alpine region, water and snow often get pushed deep under the roof tiles. I’m a bit skeptical of relying solely on the Universal Dry layer, as I don’t want to be worried about the insulation every time there is a heavy storm.

Have a nice evening.

The underlayment membrane is already waterproof. What is the downside of using plastic sheeting? OSB is acceptable but prone to defects.

But already a rafter structure with insulation between the rafters?

Or is it supposed to be a roof insulation above the rafters?

For the interior, we are now also using OSB boards in our self-build project, including insulation of the attic. Yes, they are vapor-tight when glued. You just must not cut in recessed spotlights or similar, otherwise it will no longer be airtight. Therefore, it is even better to use a vapor-permeable underlay membrane above the insulation. If the OSB boards let through some water vapor here and there, which then condenses on the underside of the underlay membrane, it could dry out again eventually.

Werner K schrieb:

Since I dislike foils, I would like to avoid using them in my new build.
For insulation, I am considering wood fiber boards like Steicoflex, with a water-repellent layer such as Steico Universal Dry on top.

Is this about the environmental aspect? Wood fiber boards contain a few percent of binders. At first glance, the mentioned manufacturer does not provide details but refers to compliance with DIN standards. So the maximum allowed amount of plastic could be included.

Breathable roofing membrane and insulation above the roof deck. This way, you can mostly avoid using plastic sheeting. A breathable membrane is installed over a large area and on a flat surface. I consider this to be quite low risk.

One might say that OSB boards (oriented strand boards) are prone to issues, but plastic sheeting is as well. The question is which one is more vulnerable, and in my view, the plastic sheeting is more prone to problems than the OSB board.

For principle reasons, I am also not a fan of plastic sheeting; a construction that requires only a minimal amount of it is ideal. This means good-quality tiles with sufficient coverage and insulation above the roof deck. If I were building...

Hello,
yes, the battens obviously depend on the situation, and yes, I am aware that there is a certain proportion of PU in the insulation material, which I can accept.