ᐅ Moisture barrier beneath the base of the wall in earth-retaining formwork

Hello
Originally, I had planned to apply perimeter insulation made of XPS on a bitumen waterproofing membrane below the plinth. I also intended to insulate the plinth itself with XPS (ribbed plaster carrier board).
On the "smooth" surface, a drainage membrane was to be installed for water runoff.

Now, I noticed today that the foundations are constructed using earth formwork, which leads to significant thickness variations. Below the plinth, there is now a very uneven surface that I probably cannot cover with extruded polystyrene (XPS).

How can I properly apply the planned waterproofing and insulation in this case? Or is a specific treatment below the plinth not necessary?

Hi,

I’ve heard of an insulation that can be injected, it’s made of small beads similar to those used in raised access floors. Unfortunately, I can’t remember what it’s called.

Daniel

Hello, I assume you want to build the house on a slab foundation without a basement. If everything is done properly, you don’t need to install any moisture barriers or insulation on the strip footings. At every new layer (slab, insulation, screed), barriers are installed anyway. If it hasn’t been done already, I would recommend covering the slab with bitumen waterproofing membranes. That will definitely be cheaper than excavating around the entire foundation on both sides and then insulating and insulating it. The benefit would be practically zero, while the costs would be very high.

Best regards,
Thommi

That makes me a bit more relieved. The base is only 30cm (12 inches) high and will later be exposed by about 20cm (8 inches) in some areas. The insulation board then only goes 10cm (4 inches) into the ground. I had in mind that it should go 50cm (20 inches) deep.

I need to check whether a moisture barrier has been installed as well. Tomorrow, the concrete for the slab will be poured.

Thanks, Thommi