ᐅ Perimeter insulation beneath the foundation slab and additional XPS insulation under the screed?

Created on: 27 Sep 2016 20:44
G
GottesJunky
Hello,

Our house construction is getting closer, but today I noticed something that I don’t quite understand. Maybe someone can clarify it for me.

Under the concrete slab (according to the structural engineer 180mm (7 inches), but probably going to be 220mm (9 inches)) there is supposed to be an 80mm (3 inches) perimeter insulation (125m² (1,345 ft²)) installed. The floor build-up according to the architect looks like this:
...
5mm (0.2 inches) carrier board
120mm (5 inches) wood fiberboard insulation, thermal conductivity class 035
20mm (0.8 inches) wood chipboard insulation, thermal conductivity class 035
10mm (0.4 inches) waterproof membrane

Now my question is:
Isn’t this a bit redundant? Wouldn’t just the 120mm (5 inches) XPS insulation board above the slab be sufficient?

It will be a standard house built according to the 2014 energy saving ordinance.

Best regards,
Rico
N
Nordlys
17 Feb 2018 15:33
First of all, Steven is right. We are talking about relatively small savings. However, without insulation beneath the foundation, it will not get damp because a bituminous membrane is applied on the concrete as a barrier. On top of that comes the screed insulation, and finally the screed.
V
Verfolger79
29 Jul 2018 13:58
Hello everyone,

I’m currently building a KFW40 house as well. Does anyone happen to have photos of installing an 8cm (3 inch) insulation layer above the basement floor slab?

I forgot to take pictures for the energy assessor. It would be great if someone could help me out. Thanks!
L
Lobster
29 Jul 2018 14:13
I only have photos of our insulation before pouring the concrete slab.

Foundation floor made of insulation panels with wooden battens, excavation pit and soil pile in the background.


Foundation with light green insulation panels, wooden strips and pipes on a construction site.
V
Verfolger79
29 Jul 2018 14:17
Thank you, but I would need photos of the insulation above the floor slab if the interior is already plastered.
L
Lobster
29 Jul 2018 14:20
We are not at that stage yet; we still have to be patient for a few more weeks.