Foam glass gravel yes/no?

Hello,

I didn't find anything in the search. My architect had planned foam glass gravel under the floor slab (without a basement) on strip foundations. However, he says that for cost reasons you can do without it and instead insulate under the screed, since the clay soil underneath should not freeze in winter.

That would save me about €5,000. From his point of view, that would be okay, but I should say whether it is okay from my perspective. I've been googling for two days now and haven't found anything useful.

What do you think?

I cannot say anything about foam glass gravel, but contrary to the initial calculation, we also decided against the under-slab insulation and are now insulating under the screed with PUR - it is significantly more expensive than regular insulation, but cheaper than the under-slab insulation with the same effect in terms of thermal protection.

We do not have foam glass gravel and instead have insulation boards under the floor slab. (Müsste Styrodur sein, weiß es aber nicht auswendig) This is also cheaper than the foam glass.

We insulate with 12cm WLG035 auf the floor slab.

Hello,

What do you think?

I mean - attention: purely my personal opinion - that it is pointless to insulate the soil; it is already crazy enough that this approach can hardly be avoided for a KfW 55 energy-efficient house (it has a calculable effect on the value). At some point, I will ask our surveyor to "re-measure" a handed-over single-family house with under-slab insulation; I am curious how the weight of the house will affect the insulation beneath the slab.

For an Energy Saving Ordinance or KfW 70 standard, you can safely do without it and have the insulation installed inside the house, on the slab. You seem to have hired a smart architect

Rhenish greetings

Thank you construction expert, another point I can cross off my "hopefully we did this correctly" list