Is front-facing insulation of the floor slab necessary?

Hello everyone,

We are about to start construction of our non-basement single-family house. The exterior wall will be made of insulating bricks (Liaplan Ultra 8) with a wall thickness of 36.5 cm (U-value: 0.20) without additional exterior insulation.

The construction of the floor slab is planned as follows:
25 cm concrete
0.5 cm bare bitumen roofing membrane
12 cm extra polystyrene XPS (0.035 W/mK)
6 cm cement screed
1.5 cm tiles

A front-side insulation of the floor slab (edge insulation) is not planned. According to the builder, this is not necessary because of the insulation auf the floor slab.
Is this statement fundamentally correct, or does a thermal bridge arise here at the floor slab/exterior wall and thus higher heating costs?

Thank you very much in advance for your help!!

Best regards
Frank123

Hello,

....A front-side insulation of the base slab (edge insulation) is not planned. According to the builder, this is not necessary because of the insulation on the base slab.

Apart from the fact that it is not a builder, but a general contractor (GU/GÜ), a look at the Energy Saving Ordinance/KfW certificate is helpful here. It is highly likely that a flat WB surcharge of 0.05 was used. This means: This detail must exactly comply with DIN 4108-2, be equivalent or better. In case of deviations, proof of equivalence is required!
Note: The accompanying external construction supervisor should pay special attention to the execution of the thermal bridges!

Best regards

Thank you for the quick response.

If I have used the wrong terminology here, I apologize – I am just a layman.

...a look into the Energieeinsparverordnung/KfW certificate is helpful here. In all likelihood, a flat WB surcharge of 0.05 was applied.

Your assumption is correct! Does this now mean that the intended insulation – if carried out properly – is acceptable, or should the planning be changed here?

...If I have used the wrong terminology here, I apologize – after all, I am just a layman.

That doesn't matter, as it applies in 99.9% of cases. There are especially significant legal differences between BT and GU/GÜ, which one should actually be clear about beforehand in the case of a construction/purchase intention.

...Your assumption is correct! Does this now mean that the intended insulation – if properly executed – is justifiable, or should the planning be changed here?

I cannot answer that question reliably, as I do not have the detailed knowledge for this.
If the WB is actually executed as per the detailed verification, there should be no reason for a complaint regarding the demand requirement (heating operation).
To what extent this actual demand, how high it is, can be realistically met should be answered by the system planner.

Best regards.