Hello 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).
Why does your XPS insulation need to fit flush against the shotcrete wall? I assume you want to install your prefabricated element already insulated at that spot, right? What is the reason against filling any possible gap between the XPS and the shotcrete wall above with concrete?
If you definitely want to fill the cavities differently, it would make sense to keep the XPS insulation and additionally fill the space, for example, with foam glass gravel – this is also a common type of perimeter insulation (usually compacted beneath floor slabs).
If you definitely want to fill the cavities differently, it would make sense to keep the XPS insulation and additionally fill the space, for example, with foam glass gravel – this is also a common type of perimeter insulation (usually compacted beneath floor slabs).
julian113 schrieb:
@dertill Thank you very much for the explanations. That already helps a lot. Is it possible to fill something like this yourself, or should it be done by a professional company? Do you happen to have a specific product name for this kind of insulation?
Our energy consultant also recommended a bituminous pearl loose-fill insulation, but it only has a thermal conductivity value (WLS) of 060.Foaming it yourself is not possible, only with suitable equipment and materials. I don’t have a specific product name for that; usually, it’s used for blown-in insulation, but even there it’s rather rare because it’s more expensive compared to granules and flakes.
Regarding the use of loose-fill insulation in the ground: in principle, it’s possible, but I would always pay attention to the approval or certification of the specific insulation material, especially for these kinds of applications—otherwise, you might run into problems later if something goes wrong. I’m also not entirely sure how the construction is intended or what the exact situation is.
From the neighbor’s basement interior to your basement interior: old concrete basement wall -> shotcrete wall with vertical offset downward -> uneven areas to be filled -> XPS insulation from the prefabricated basement -> waterproof concrete basement wall, all starting from the shotcrete wall with a new concrete floor. Correct?
In that case, the insulation value of the material used to fill the gaps doesn’t really matter because those areas were not originally planned for insulation; rather, the XPS should be attached directly. Or does the XPS insulation need to be thinner as a result? How large are the uneven areas, or is there a continuous gap remaining? Alternatively, would it make sense to smooth over with cement plaster first before placing the basement wall?
J
julian11312 Apr 2023 09:08@dertill Exactly, the construction is precisely correct as described. However, the shotcrete wall not only has a downward offset but also extends longer on the sides than the neighboring basement.
The problem is that the original XPS insulation, which was supposed to be factory-installed on the precast wall, does not fit into the cavity. A 16cm (6.3 inches) XPS insulation was originally planned. However, because the shotcrete wall has a significant wave (about 10-12cm (4-5 inches)), only about 6-8cm (2.4-3.1 inches) fits fully over the surface. The initial plan was to straighten (grind) the shotcrete wall, but due to the fragile and old condition of the neighboring house, we cannot do that. Therefore, we now face the situation that at the thinnest point there is only around 6-8cm (2.4-3.1 inches) of space between the shotcrete wall and the precast wall, so the factory-installed 16cm (6.3 inches) XPS insulation does not fit.
On the other three walls, the situation is uncritical; if necessary, to compensate for potentially thinner insulation on the party wall (to meet the building energy regulations), according to the energy consultant, we can add more insulation, and in the worst case, we could switch to internal wall insulation on the party wall. However, we originally wanted to use this only as a last-resort option and thought that the cavity might still be usable for insulation.
The problem is that the original XPS insulation, which was supposed to be factory-installed on the precast wall, does not fit into the cavity. A 16cm (6.3 inches) XPS insulation was originally planned. However, because the shotcrete wall has a significant wave (about 10-12cm (4-5 inches)), only about 6-8cm (2.4-3.1 inches) fits fully over the surface. The initial plan was to straighten (grind) the shotcrete wall, but due to the fragile and old condition of the neighboring house, we cannot do that. Therefore, we now face the situation that at the thinnest point there is only around 6-8cm (2.4-3.1 inches) of space between the shotcrete wall and the precast wall, so the factory-installed 16cm (6.3 inches) XPS insulation does not fit.
On the other three walls, the situation is uncritical; if necessary, to compensate for potentially thinner insulation on the party wall (to meet the building energy regulations), according to the energy consultant, we can add more insulation, and in the worst case, we could switch to internal wall insulation on the party wall. However, we originally wanted to use this only as a last-resort option and thought that the cavity might still be usable for insulation.
So you can’t simply place your house or basement wall 8cm (3 inches) further away? Are you restricted all around by the building boundary or other developments? Otherwise, this would be much easier, even if you might have to submit a revised plan to the building authority (building permit/planning permission). You would then need to upgrade the party wall insulation accordingly, but that certainly wouldn’t be a disadvantage.
Otherwise, if this is still even possible now, you could construct the basement walls with cavity insulation – then you wouldn’t have to use XPS, but could also use Neopor or PUR insulation, which would allow you to reduce the insulation thickness by about 40 to 50%.
Otherwise, if this is still even possible now, you could construct the basement walls with cavity insulation – then you wouldn’t have to use XPS, but could also use Neopor or PUR insulation, which would allow you to reduce the insulation thickness by about 40 to 50%.
Addendum: If cavity insulation is no longer possible and moving the house is also not an option, it might be conceivable to use something like Jackodur Plus (WLG027) as perimeter insulation – as long as it is not load-bearing, the product is also approved as perimeter insulation and could be applied significantly thinner.
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