ᐅ Moisture in aerated concrete exterior walls: Should interior plaster/floor screed be applied first, followed by the external thermal insulation composite system (ETICS)?

Hello everyone,

We were unable to waterproof the flat roof of the penthouse, and it has been raining for several days now. This has caused water to enter the house in some areas, and due to the lack of roof overhang, the exterior walls (clay sandstone) are also getting wet.

The plan is to waterproof the roof once it has been dry for a few days, and by mid to late this month, both the interior plaster and the screed will be installed. After that, the moisture inside the house should dissipate, and before it gets too cold, the external thermal insulation composite system (ETICS) will be applied on the outside. The idea is to allow the moisture to escape through the walls.

Now, I’m wondering if this approach makes sense. It’s currently raining frequently, so the walls are getting wet from the outside. As far as I know, not much moisture should be transported through the stone. Wouldn’t it be more sensible to first waterproof the roof, then apply the ETICS, and only after that install the interior plaster? That way, the exterior walls wouldn’t get wet anymore, which would also protect the interior plaster from issues like frost.

What are your thoughts? What are the pros and cons of each option, and which would you lean towards?

Cheers,
M. Gerd