Control where a layer applies

With rooms in the model, set the model default to a preset that has exterior insulation.

Orbit below the room and look up at its floor. The yellow material layer filling the floor below is the insulation — right now it wraps the floor too.

In Detail Defaults, press Override (the pencil icon) on the preset. Under the Slab section detail, find “Core·Inside-Outside” and press Override on it too — without that you can only pick another built-in preset.

Find the field named “Outside Is” and change it from Any to Above. The floor insulation disappears — down there the outside is below, not above, so the layer no longer applies. The other conditions work the same way; try them.