ᐅ Is it effective to use 80mm aluminum-faced EPS insulation over a torch-applied waterproofing membrane?

Hello.

In the basement, EPS insulation (80mm (3 inches)) is currently planned above the waterproofing membrane.

Is it sensible or recommended to use an aluminum-foil-faced variant (PUR) here, or is it unnecessary? The cost would be twice as much.

In principle, the waterproofing membrane should seal properly, but can moisture still get through?

Thank you.

When moisture occurs, the PUR board does not help either. The aluminum-coated layer is intended to reflect the heat from the underfloor heating upwards.

Yes, it is unnecessary. The airtightness is ensured by the bitumen layer/sheet waterproofing. Insulation in front of it protects this sealing. In front of that comes a drainage membrane, which in turn protects the insulation.
Are you sure it is EPS? For perimeter insulation, XPS is usually used because of its compressive strength and durability. I would also consider making it a bit thicker, especially if the basement is intended for more than just storage use.

@Alex85 I think he is talking about insulation under the screed, right? But you mean the perimeter insulation from the outside.

Correct. I mean insulation on the ground slab. There is already XPS insulation under the slab.

Ah, okay, I misread that.