ᐅ Insulating the foundation slab – ceiling height is insufficient

Hello everyone,

We are considering buying my mother-in-law’s half-timbered house, as it is currently vacant.
The house is technically at the 1944 standard, so basically everything needs to be redone.

Here is our problem or question:
On the ground floor, several rooms have a concrete ceiling with a basement underneath. On top of that are beams, sometimes insulated with glass wool or mineral wool, then chipboard and PVC flooring. The total height is about 15cm (6 inches).
There is another room below without a basement. It has a concrete floor with PVC flooring on top.

Since the ceiling height is limited (doorway height 1.99m (6 ft 6 in), ceiling height about 2.2m (7 ft 3 in)), adding insulation will be difficult.

Therefore, our question is: How critical is it if a single room in the house is left without insulation underneath?
Attached are the floor plan of the ground floor (the room outlined in red) and a photo of the room.

Maybe someone has an idea without having to replace the entire slab?

I would first check whether it is actually a concrete slab or just a screed on the ground. In timber-framed houses, a concrete slab is usually not poured. If it is only a cast floor surface, remove it. Depending on the foundation arrangement, the new floor can also be set deeper to gain ceiling height.

Thank you! I’m also considering whether it might be a good idea to remove the debris. No idea if the house would collapse then.

My father-in-law just called again; he remembered something else:
There might be a filled-in cellar under the room, but no one knows for sure. In any case, he says the floor is made of "rammed concrete."

Take a look at dry systems for underfloor heating with insulation.

For example, Cosmo Top 15 provides some insulation and additionally a warm floor with minimal installation height.

Rammed concrete for a floor??? I think he simply means an unreinforced floor slab. If it is a genuine timber-framed house, then the slab does not serve a structural purpose.

There are vacuum insulation panels starting at 10 mm (0.4 inches) thickness, which correspond to 50 mm (2 inches) of conventional insulation. However, these must fit precisely, as they cannot be cut.

So, remove the old covering, check if you can go deeper (in the screed), possibly use leveling compound to smooth the surface, install the vacuum insulation panels, and then apply a thin covering (such as linoleum) on top.