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?
K
Knallkörper22 Jun 2018 10:35Regarding the ground conditions, you probably have temporarily accumulating seepage water...
K
Knallkörper22 Jun 2018 12:57Snowy36 schrieb:
However, the manufacturer of the panels specifies the coating on their website.If this is stated in the official product datasheets, then the installer must comply. Period! This makes any discussion about the load case "draining seepage water" unnecessary – which you would need to prove anyway. If you have a waterproof concrete basin (white tank), I would consider it unproblematic, but you didn’t mention anything about that.
Snowy36 schrieb:
(...)
For the insulation of the concrete basement...n
(...)
Nowadays, more and more people are building in this region (and other construction areas), and we have noticed that in most houses, a black coating is applied before installing the insulation boards...It is possible that the other houses simply have a different basement wall construction, namely masonry instead of a concrete ("white tank") basement.
WU concrete (waterproof concrete) is impermeable to liquid water but not to water vapor. According to the "shot glass formula" (an S-glass amount of water per day per square meter), a small amount of water may diffuse through WU concrete. This is then "ventilated away."
An additional bitumen coating can prevent this. However, this is a belt-and-braces approach. It is not necessary but does no harm—especially in the case of unplanned cracks and defects—provided it is part of a planned white-tank concept.
From personal experience:
In our case, the basement will be below ground level. One option is the solution compliant with DIN standards (bituminous thick coating), the other is the practical approach. We had the choice to have it or not (also on a slope). The option with it would have cost us an additional 3,000€ net. We decided against it because the structural builder, architect, and construction supervisor believe that the slabs do not require this extra measure due to the soil pressure and the waterproof concrete basement.
In our case, the basement will be below ground level. One option is the solution compliant with DIN standards (bituminous thick coating), the other is the practical approach. We had the choice to have it or not (also on a slope). The option with it would have cost us an additional 3,000€ net. We decided against it because the structural builder, architect, and construction supervisor believe that the slabs do not require this extra measure due to the soil pressure and the waterproof concrete basement.
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