J
julian11310 Apr 2023 23:34Hello everyone,
We have the following issue with our new build.
We are currently constructing a new semi-detached house attached to an existing semi-detached house. Since the existing semi-detached house is quite old and only has a very shallow basement, we had to install a shotcrete wall in the earth area in front of the neighboring semi-detached house’s original basement.
We now want to build our basement against this shotcrete wall, which will be larger in all directions than the basement of the old semi-detached house.
Our problem is that the shotcrete wall is far from even, and the original plan to place our new prefabricated basement—including XPS exterior wall insulation—flat against the shotcrete wall isn’t working. Therefore, we are currently considering whether it might be possible to compensate for the unevenness with a different type of insulation that can fill the gaps well between our new prefabricated house wall and the shotcrete wall, and which is not as rigid as the XPS boards. According to the building energy regulations, we need insulation with a thermal conductivity of 0.045 W/(m·K) (WLS 045).
Are there options for more flexible insulation materials to use between the shotcrete wall and the basement wall, such as loose-fill insulation, bonded insulation, or something similar, to fill the gaps properly?
Or could we, if necessary, replace the planned exterior wall insulation with interior wall insulation inside the basement?
Oh, and the basement is being constructed as a waterproofed basement (WU basement). During excavation, groundwater did not appear and is currently apparently about 50cm (20 inches) lower, but according to the soil report, the groundwater level is about 25cm (10 inches) above the underside of the floor slab—so roughly at the level of the top of the floor slab (which is 25cm (10 inches) thick).
We have the following issue with our new build.
We are currently constructing a new semi-detached house attached to an existing semi-detached house. Since the existing semi-detached house is quite old and only has a very shallow basement, we had to install a shotcrete wall in the earth area in front of the neighboring semi-detached house’s original basement.
We now want to build our basement against this shotcrete wall, which will be larger in all directions than the basement of the old semi-detached house.
Our problem is that the shotcrete wall is far from even, and the original plan to place our new prefabricated basement—including XPS exterior wall insulation—flat against the shotcrete wall isn’t working. Therefore, we are currently considering whether it might be possible to compensate for the unevenness with a different type of insulation that can fill the gaps well between our new prefabricated house wall and the shotcrete wall, and which is not as rigid as the XPS boards. According to the building energy regulations, we need insulation with a thermal conductivity of 0.045 W/(m·K) (WLS 045).
Are there options for more flexible insulation materials to use between the shotcrete wall and the basement wall, such as loose-fill insulation, bonded insulation, or something similar, to fill the gaps properly?
Or could we, if necessary, replace the planned exterior wall insulation with interior wall insulation inside the basement?
Oh, and the basement is being constructed as a waterproofed basement (WU basement). During excavation, groundwater did not appear and is currently apparently about 50cm (20 inches) lower, but according to the soil report, the groundwater level is about 25cm (10 inches) above the underside of the floor slab—so roughly at the level of the top of the floor slab (which is 25cm (10 inches) thick).
The entire project of adding a basement to an existing semi-detached house, along with the different dimensions involved, is inherently prone to errors – but others here know more about that.
For insulation in the ground, I would avoid using loose fill. These materials are also not approved for that purpose. As an alternative to XPS boards, if they do not fit flush, there is the option of PUR/PIR foam insulation applied by injection after the prefabricated wall is in place. The material is injected as a liquid, then expands and fills every cavity. It is basically like construction foam. However, it is significantly less pressure-resistant than XPS. But if that is sufficient, it would be a cavity-filling, non-decomposing alternative that can also be used underground. The thermal conductivity value (WLS) for pure PUR is 0.028, so this should be adequate.
For insulation in the ground, I would avoid using loose fill. These materials are also not approved for that purpose. As an alternative to XPS boards, if they do not fit flush, there is the option of PUR/PIR foam insulation applied by injection after the prefabricated wall is in place. The material is injected as a liquid, then expands and fills every cavity. It is basically like construction foam. However, it is significantly less pressure-resistant than XPS. But if that is sufficient, it would be a cavity-filling, non-decomposing alternative that can also be used underground. The thermal conductivity value (WLS) for pure PUR is 0.028, so this should be adequate.
J
julian11311 Apr 2023 16:50@dertill Thank you for the explanations. That already helps a lot. Can you apply something like this yourself, or should it be done by a professional company? Do you possibly have the exact product name of this type of insulation?
Our energy consultant also recommended a Bituperl loose-fill insulation, but it also has a thermal conductivity value (WLS) of 0.060.
Our energy consultant also recommended a Bituperl loose-fill insulation, but it also has a thermal conductivity value (WLS) of 0.060.
J
julian11311 Apr 2023 16:58@Tolentino We have a lean concrete leveling layer. It was just poured last week and is flush with the shotcrete wall. There is no contact with the soil underneath, but theoretically there could be contact at the sides if nothing is built there beforehand.
Oh right, the prefabricated elements actually form an enclosed space by themselves.
Personally, I didn’t know that loose fill materials can’t be used for soil backfill. But thinking about it, it makes sense because roots can easily grow through the loose fill and damage the insulation itself, as well as cause secondary damage like water infiltration, ultimately destroying the insulation.
So, the loose fill would probably need to be fully enclosed all around, and then the question remains whether the foam-in-place option suggested by [USER=44867]@dertill might actually be simpler and even more cost-effective.
It’s strange that your energy consultant didn’t know that either.
Personally, I didn’t know that loose fill materials can’t be used for soil backfill. But thinking about it, it makes sense because roots can easily grow through the loose fill and damage the insulation itself, as well as cause secondary damage like water infiltration, ultimately destroying the insulation.
So, the loose fill would probably need to be fully enclosed all around, and then the question remains whether the foam-in-place option suggested by [USER=44867]@dertill might actually be simpler and even more cost-effective.
It’s strange that your energy consultant didn’t know that either.
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