Adding an upper floor. Same stone as the ground floor? Insulation of the existing structure?

When I then spoke with a construction company and a structural engineer, both said I shouldn't use KS, but rather a 24cm pumice block like the existing structure. However, both also recommend full thermal insulation.

I would also recommend pumice and - typically for me :D - external insulation of the facade; it doesn't have to be ETICS. Apart from the fact that pumice is a natural building material, in my view it makes little sense to create a mixed masonry; especially since pumice and KS have opposing advantages. You have to apply insulation anyway, so soundproofing - given the later overall thickness of the wall structure - no longer plays a role. Rhine regards

Ok thanks, that is already a statement. So you clearly recommend pumice? Although KS is also a natural stone. I was told pumice would feel warmer on the walls. Unfortunately, I cannot check this on the house because the walls are covered with drywall. In your opinion, is a 10 cm insulation sufficient? I want to avoid the window recesses becoming too deep.

So you clearly recommend pumice?

Yes, I always tend to side more with the structural engineer than with the architect; it is certainly safer in the long run. Besides, pumice is – from my point of view – a good, albeit underrated building material, and I wouldn’t know any logical reason to deviate from it.

In your opinion, is 10 cm insulation enough? I want to avoid the window reveals becoming too deep.

Answering that would be reckless; it must be calculated for the specific building!

For example, we insulated under the roof with WLG 032 (out of necessity, since we did not want to double the rafters too much at the expense of the living space below) and, logically, the exterior envelope is getting appropriate 12 cm insulation.

Rhenish regards