Hello everyone,
We are managing our build with individual contracts and have hired a very reputable local shell construction company for the structural work. We did not commission a soil survey before starting construction because the municipality had already drilled on our plot and found that the ground consists of clay and silt.
We are building a KFW 55 house with a basement. Two of the basement rooms have daylight due to a slight slope and are intended to be living spaces with underfloor heating, etc.
For insulating the concrete basement, XPS boards from the company Austrotherm were used. The whole process was supervised by a construction manager.
Now, in our region (in other development areas), more and more people are building, and we noticed that, in most houses, a black coating is applied before the insulation boards are installed, and only then are the boards attached. This was not done in our case; the boards were fixed with mechanical fasteners without this layer.
Both the construction manager and the shell contractor independently say that since we do not have any groundwater pressure, this coating is not necessary.
Am I worrying for nothing, or should I have all the boards removed (would they be reusable or would I have to use new ones?) at my own expense and apply the coating afterward?
The basement has not been backfilled yet.
The contract specifies point fastening, but it does not clearly state whether a bitumen layer or something similar should be applied in between. However, the manufacturer of the boards specifies the coating on their website.
How was this handled in your projects?
We are managing our build with individual contracts and have hired a very reputable local shell construction company for the structural work. We did not commission a soil survey before starting construction because the municipality had already drilled on our plot and found that the ground consists of clay and silt.
We are building a KFW 55 house with a basement. Two of the basement rooms have daylight due to a slight slope and are intended to be living spaces with underfloor heating, etc.
For insulating the concrete basement, XPS boards from the company Austrotherm were used. The whole process was supervised by a construction manager.
Now, in our region (in other development areas), more and more people are building, and we noticed that, in most houses, a black coating is applied before the insulation boards are installed, and only then are the boards attached. This was not done in our case; the boards were fixed with mechanical fasteners without this layer.
Both the construction manager and the shell contractor independently say that since we do not have any groundwater pressure, this coating is not necessary.
Am I worrying for nothing, or should I have all the boards removed (would they be reusable or would I have to use new ones?) at my own expense and apply the coating afterward?
The basement has not been backfilled yet.
The contract specifies point fastening, but it does not clearly state whether a bitumen layer or something similar should be applied in between. However, the manufacturer of the boards specifies the coating on their website.
How was this handled in your projects?
Knallkörper schrieb:
If this is stated in the "official" product datasheets, then the contractor must comply. Period! That eliminates the discussion about the load case "seeping drained water"—which you would have to prove if in doubt. If you have a waterproof concrete shell ("white tank"), I would consider that uncritical, but you didn’t mention that.Yes, I think we have a white tank... cast-in-place concrete (waterproof) and then the slabs on top...
Yes, and I would initially agree with you: please follow the manufacturer’s instructions...
However, I’ve also noticed that for other things this often only applies in theory, for example with the dimpled membrane... everyone seems to do it differently anyway.
Zaba12 schrieb:
From my own experience: decided because the structural builder, architect, and construction supervisor believe that the panels do not require this additional element due to the pressing force of the soil and the waterproof concrete basement.Oh, thanks Zaba, that eases my concerns a bit that I must have been completely crazy to trust the construction supervisor and structural builder... but today an expert will come again just to be sure.
Otus11 schrieb:
WU concrete is impermeable to liquid water but not to water vapor. According to the "shot glass formula" (an S-glass of water per day per square meter), a small amount of water vapor is allowed to diffuse through WU concrete. This moisture is then "vented away."
We have a controlled residential ventilation system – even in the basement – so this requirement is already met.K
Knallkörper22 Jun 2018 13:32Snowy36 schrieb:
Yes, I think we have a waterproof concrete basement box....Sorry – that sounds somewhat naive. You should know that. Who is responsible for the planning?
Zaba12 schrieb:
From my own experience:
Only that in our case the basement will be below ground level. One thing is the solution according to the DIN standard (bituminous thick coating), the other is the practical approach. We had the choice with or without (also on a slope). The option with it would have cost us 3,000 euros net more. We decided against it because the structural engineer, architect, and construction supervisor believe that the slabs, due to the soil’s pressing force and the waterproof concrete basement, do not require this additional measure.With clayey-silty soil, I would have my doubts. We built ourselves on similar conditions; the soil really channels a lot of water after rainfall, and it lasts for several days. The neighbor’s basement then has water up to 1.80 m (6 feet) high against it. The insulation needs to be firmly fixed to prevent it from “floating.” More than half of the houses with basements in such conditions have or had issues with water ingress (some had to be dug out again). At least under those soil conditions, I would have invested the 3,000 euros instead of knowingly accepting a construction that does not comply with recognized building standards and could potentially cause a real defect. If the basement is constantly slightly damp, you will face a considerable reduction in market value when selling.
Knallkörper schrieb:
Sorry – that sounds somewhat naive. This is something you should know. Who commissioned the planning?
I would have concerns with clayey-silty soil. We have built on similar conditions ourselves; the soil actually retains a lot of water for several days after rainfall. At the neighbor’s, the water rises up to 1.80 m (6 feet) against the basement wall. The insulation needs to be firmly secured so it doesn’t "float." More than half of the basements built on such soil have had—or still have—issues with water ingress (some were even excavated again). At least with this type of soil, I would have invested the 3,000 euros instead of knowingly accepting a construction that does not comply with recognized technical standards and that could cause a real defect. If the basement remains slightly damp over time, you will face a significant reduction in value when selling the property... We have a slope within the building plot. How would water stand there? Doesn’t the land slope away from the house downhill? The soil report has just arrived, so I can discuss this again with the shell contractor and the architect.
Knallkörper schrieb:
Sorry – that sounds somewhat naive. You are supposed to know something like that. Who commissioned the planning?
I would first need to check the exact clause in the shell builder’s offer to see what exactly is stated... it’s unlikely that “watertight concrete structure” would be explicitly mentioned there...
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