ᐅ What is the best way to construct the floor assembly?

Created on: 4 Jul 2018 14:28
S
Snowy36
S
Snowy36
4 Jul 2018 14:28
Hello everyone,

Do you all have a vapor barrier under the raw subfloor, something like the Katja Sprint sealing membrane from Knauf?

In our case, in the basement, there will be an Alujet foil placed directly on the XPS insulation (so without the membrane). On the ground floor and upper floor, Styrofoam will be used instead of XPS on the raw subfloor, but again, without those black membranes.

However, our neighbors had those black membranes glued to their raw subfloor (though they don’t have a basement).

Can anyone tell me what the difference is? Should I insist on having those membranes installed? What do you think about installing/gluing them yourself?
KingSong4 Jul 2018 15:01
We are building without a basement and have exactly this "Katja Sprint" vapor barrier on the raw subfloor. We were told that this vapor barrier is intended to prevent rising residual moisture from the concrete slab.
S
Snowy36
4 Jul 2018 15:11
But then this would actually be mandatory, right?

I wish someone would just do what is standard on my house once... (-:
KingSong4 Jul 2018 15:16
No idea if this is standard, but what is really standard in house construction?
K
Knallkörper
4 Jul 2018 15:16
The bottom foundation slab / floor slab must be sealed to prevent moisture from the ground penetrating the floor structure. Conversely, intermediate ceilings do not need to be sealed. I am not sure if the Alujet foil is suitable for this purpose. There are many different types of Alujet. I also don’t know whether it is allowed to install it directly on the raw concrete or if it is permissible to lay it on top of the XPS insulation boards. Personally, I would prefer to place it beneath the XPS boards.
S
Snowy36
4 Jul 2018 15:35
Ok, so I now understand that this only needs to be done on the slab foundation, not on the ground floor and upper floor in my case....(-:

This time, I just want to prevent it from being done the way someone thinks they always do it, like with the roof, and then ending up with issues afterwards...

If I approach this with common sense, I wouldn’t want any water on the XPS boards if it can be avoided, so the waterproofing (whether Katja or Alujet) should go in front of them.