Removable roof insulation

Dear insulation experts

I am new here and facing my first major project:

Together with some friends, we want to buy and make habitable 3 old barns (so-called Rustici) in southern Switzerland. Both the shell and the roofs of these Rustici consist exclusively of gneiss slabs. These roofs are extremely durable and stable, but individual displaced stones can cause them to become leaky. There are only a few specialized roofers left who are familiar with such roofs, but they can make them watertight again by carefully repositioning the stones. However, they need to be able to inspect the roof from the inside.
This brings me to our challenge: We want to insulate the roof from the inside, but preferably with a construction that can be removed relatively easily (in case something becomes leaky).

I am very grateful for your ideas. I have thought of the following:

- Clamp insulation mats between the rafters and thus directly under the gneiss slabs, then screw OSB boards onto the rafters (also as vapor barriers)

- Even more elegant would be to apply insulation material directly onto the OSB boards, then the whole construction could be removed at once. Which insulation material would be suitable for that?

What do you think of the idea? As mentioned, I am no expert and therefore very grateful for tips!

Best regards

Since Rusticis seem to be a big topic with you in Switzerland, I would look for an experienced planner/office and roofer there. There are certainly tested/approved concepts available there. Everything else can only go wrong, especially a solution whose basis is already that it does not work.

Hello Lumpi We need an experienced roofer anyway - whether it is to maintain the roof (i.e. watertight) or to completely reroof it. We also have an architect. However, he would only design a project that involves completely stripping the roof and a fixed under-roof structure. He said you can also tinker, but for legal reasons he does not design this. We could also imagine completely reroofing the roof, but from our point of view that does not solve the problem: We might have peace for 20 years, but after that we might still be at the point where the roof is no longer watertight, and we have a fixed under-roof. I am not expecting any patent solutions now from the community, but especially ideas on how to approach the described option. Of course, we would then discuss these further with roofers and architects. What do you mean by "solutions that do not work"? Or what can go wrong? - Under-roof does not insulate as expected - Insulation forms mold because of condensation?

I mean that the basis of your planning is that the roof will eventually leak and everything will have to be torn out again. That's not how I would design a house. Your architect sees it the same way: "for legal reasons..." simply means that he thinks it won't work and doesn't want to be liable for the already expected damages.

The roof eventually becomes leaky because it consists of "movable tiles" and because it easily exceeds the lifespan of modern roofs. The basis of my planning is precisely not that I have to throw everything out when it becomes leaky, but that the sub-roof can be removed, the issue fixed, and the sub-roof put back in place! If we were to completely rebuild it, we would still have to use natural stone again (as required) and eventually face the same problem. I see your point, but I want to plan with foresight as much as possible.

What happens if a brick shifts slightly, the roof becomes leaky, and you don't notice it? Then the entire insulation is ruined and rots. Only a professional can give you good advice on that.