ᐅ Strip foundation with additional perimeter insulation and waterproofing
Created on: 16 Apr 2023 13:04
K
Kati2022
Hello everyone,
Since our contractors have different opinions, I would like to ask for your views and experiences.
Problem:
We are building a house without a basement. Foundation – strip footings around 80cm (31.5 inches) deep. The footings are insulated with 12cm (5 inches) perimeter XPS both from the outside and inside. Under the slab, there is also 12cm (5 inches) of XPS insulation. Since the house is located at the highest point of the new development, our site manager believes we don’t need drainage. The site manager and the structural carpenter say that the exterior perimeter insulation does NOT need to be covered with an additional waterproofing layer. Installing a dimple membrane for plaster protection is optional. The plasterer is supposed to apply a waterproof slurry in the base area, and that should be enough. Hmm... Is that sufficient? Do the XPS boards protect the strip footings permanently? The window installer insists that he would definitely coat the footings with a bitumen layer and extend the dimple membrane all the way down to about 80cm (31.5 inches).
How have you waterproofed your strip footings (without basement)?
Since our contractors have different opinions, I would like to ask for your views and experiences.
Problem:
We are building a house without a basement. Foundation – strip footings around 80cm (31.5 inches) deep. The footings are insulated with 12cm (5 inches) perimeter XPS both from the outside and inside. Under the slab, there is also 12cm (5 inches) of XPS insulation. Since the house is located at the highest point of the new development, our site manager believes we don’t need drainage. The site manager and the structural carpenter say that the exterior perimeter insulation does NOT need to be covered with an additional waterproofing layer. Installing a dimple membrane for plaster protection is optional. The plasterer is supposed to apply a waterproof slurry in the base area, and that should be enough. Hmm... Is that sufficient? Do the XPS boards protect the strip footings permanently? The window installer insists that he would definitely coat the footings with a bitumen layer and extend the dimple membrane all the way down to about 80cm (31.5 inches).
How have you waterproofed your strip footings (without basement)?
Allthewayup schrieb:
A dimpled membrane does not serve as a plaster protection layer, but as a backfill protection in the soil and ends where the plaster begins. Maybe there was a misunderstanding. Yes, I expressed myself incorrectly here. Of course, it was about the "backfill protection."
Harakiri schrieb:
What might be necessary is waterproofing of the strip foundations (i.e. before installing the insulation boards), if required due to the relevant water exposure class (ground moisture, occasionally pressurized water, etc.) and if they are not inherently resistant (such as waterproof concrete construction). However, this mostly concerns potential rising moisture from the strip foundation to the floor slab, and you will most likely have appropriate waterproofing on the floor slab anyway. Waterproofing could not be done before installing the insulation boards because the XPS boards were attached directly during the pouring of the foundations (acting like a formwork, on both sides). The floor slab is, of course, protected by a sheet membrane. Inside the house, the Katjafolie membrane will still be installed.
Then you don’t need to think about it further – waterproofing on insulation boards does not provide permanent protection against water infiltration, so you can skip that. Make sure the perimeter insulation boards are installed without gaps, and if necessary, fill any small gaps with foam (as long as the gap isn’t too large), then apply a dimpled membrane and that’s it.
How far should your concrete slab extend at the edges? If you have floor-to-ceiling windows and doors, you may need to check that the waterproofing (definitely applied directly on the slab, the recessed slab profile, and the wall, before insulation) extends far enough down.
How far should your concrete slab extend at the edges? If you have floor-to-ceiling windows and doors, you may need to check that the waterproofing (definitely applied directly on the slab, the recessed slab profile, and the wall, before insulation) extends far enough down.
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Allthewayup16 Apr 2023 18:16At this point, I also want to clarify that I was referring to the part of the foundation slab that will be located underground and extends up to the ground level—meaning the exterior sides around the foundation slab, not underneath it. This area must be sealed directly on the concrete/brick from the outside. As others have already mentioned, sealing on top of the XPS insulation boards is just a placebo. The strip footing itself does not require any special waterproofing. On the inside of the foundation slab—meaning the raw concrete—the moisture barrier against rising damp will be applied, as some forum members have also pointed out.
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Allthewayup16 Apr 2023 18:20Kati2022 schrieb:
Yes, I didn’t express myself clearly here. Of course, it was about the "backfill protection."
It couldn’t be sealed before bonding the insulation boards because the XPS boards were installed directly during the foundation pouring (acting like a kind of formwork on both sides). The slab is, of course, protected by a vapor barrier film. Inside the house, the Katjafolie will still be installed. As you describe it, this matches the typical composition of a slab foundation: PE film, XPS insulation, reinforcement, and then the concrete is poured. The formwork is on the outside. Just to clarify: Were the strip footings poured together with the slab in one operation?
I just checked the structural plans. The concrete strength for the slab and foundations is C25/30. I assume this is standard, right?
Harakiri schrieb:Yes, we’re paying close attention to that. One spot (at the multi-branch entry) is somewhat poorly insulated. The team definitely needs to improve that.
Make sure the perimeter insulation boards are installed without gaps; if necessary, have them foamed in (as long as the gap isn’t too large), then apply the dimpled membrane and that’s it.
Harakiri schrieb:Floor-level windows are sealed with Enkopur, the liquid membrane.
You have to check in the area of floor-level windows and doors that the waterproofing (definitely applied directly on the slab, slab edge profile, and wall before insulation) extends far enough downward.
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