Perimeter insulation - possibilities

Why does your XPS insulation have to lie flush against the sprayed concrete wall? I assume you want to set up your prefabricated element there already insulated, right? What speaks against filling the possible gap between the XPS and the sprayed concrete wall on top with concrete?

If you absolutely want to fill the cavities otherwise, it would also make sense to keep the XPS insulation and additionally fill, for example, foam glass gravel – which is also a common perimeter insulation (usually compacted under floor slabs).

Thank you very much for the explanations. That already helps. Can you fill something like this yourself, or should it be done by a professional company? Do you perhaps have an exact product name for such insulation?

Our energy consultant also recommended a Bituperl loose-fill insulation, but that is only WLS 060 as well.

Self-foaming is not possible, only with suitable equipment and material. I don’t have a product name for that; usually, it is used for blown-in insulation, but even there rather rarely because it is more expensive compared to granulates and flakes.

Regarding the use of loose-fill insulation in the ground: in principle, it is possible, but I would always pay attention to the approval of the respective insulation material, especially at such spots, otherwise, you might be in trouble later if something happens. I am also not quite sure how the construction is intended or how the situation presents itself. From the neighbor’s basement interior to your basement interior: old concrete basement wall -> shotcrete wall with depth offset downwards -> unevenness to be filled -> XPS from the prefabricated basement -> waterproof basement wall, the whole thing starting from the shotcrete wall with a new concrete floor. Correct? Then the insulation value of the material used to fill in is "irrelevant" because those spots were actually not planned, but the XPS should lie directly against it. Or does the XPS insulation need to be thinner as a result? And how large are the unevenness, or does a continuous gap remain? Alternatively, once apply cement plaster over it and smooth it before installing the basement wall?

Exactly, the construction is exactly right. However, the shotcrete wall not only has an offset downward but is also longer on the sides than the neighboring basement.

The problem is that the original XPS insulation, which should already be mounted factory-installed on the precast wall, does not fit into the cavity. Actually, 16cm XPS insulation was planned. But since the shotcrete wall really has a strong wave in it (about 10-12cm), only about 6-8cm fit fully across. The plan was actually to straighten (mill) the shotcrete wall now, but due to the fragile and old situation of the neighboring house, we cannot do that. Thus, we are unfortunately now facing the situation that at the thinnest point, there is only about 6-8cm space between the shotcrete wall and the precast wall, so that the factory-installed 16cm XPS insulation does not fit.

On the other three walls, the situation is uncritical, as we can possibly compensate for the potentially thinner insulation on the party wall (to meet the Building Energy Act requirements) according to the energy consultant by adding more insulation, and in the worst case, we could also resort to interior wall insulation on the party wall. However, we actually only wanted to do that as an emergency option and thought that the cavity could still be used for insulation.

That means you can’t just place your house or basement wall 8 cm further away? Are you limited all around by building windows or other developments? Otherwise, this would be significantly easier, even if you might have to submit a [Tektur] to the building authority. You would then have to upgrade the party wall insulation accordingly, but that certainly wouldn’t be a disadvantage.

Otherwise, one could (if this is still even conceivable now) execute the basement walls with cavity insulation – then you don’t have to use XPS, but can also use Neopor or PUR insulation, thereby saving certainly 40 to 50% in insulation thickness.

Addendum: If core 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 executed significantly thinner.