KFW 55 - Insulation under the floor slab

if the insulation is not sufficient and exceeds the value (average u-value or W/m²K) of 0.259, there is no funding.

Do you mean the U-value of the floor slab?

Here we also have 0.218 W/(m²K)

Hi,

how did you insulate your floor slab in the end?

Just came from my energy consultant and he tells me that because of the extremely high thermal bridge surcharges of a top-insulated floor slab, I will not achieve Kfw55. U-values are not a problem at all, but unfortunately the thermal bridge surcharges are much too high with insulation above the floor slab. Can that be? Or how do you achieve Kfw55 with insulation above the floor slab?

Well.. I am just above KfW 40 with insulation above the floor slab. It depends on the details and the rest of the house.

Well.. I am just above kfw 40 with insulation above the floor slab. It depends on the details and the rest of the house.

Could it be that you have different construction methods?

My data

Heated volume 1055m³
Usable area 330m³ fully basement
Living area 185m³

U-values:
Roof 0.15
Exterior wall 0.20 (42.5 T9)
Basement wall 0.24
Floor slab 0.25
Thermal bridge surcharge ???

Brine-water heat pump (trench collector) with controlled residential ventilation with heat recovery.

And as said, it seems that the insulation of the floor slab makes such a big difference with the thermal bridges.
The energy consultant says the thermal bridge surcharges make such a big impact especially on the floor slab that better exterior insulation does not help either.
Are thermal bridges really that relevant for kfw55?