KFW 40 / 40 plus insulation of the floor slab

Hello everyone,
we are planning a new building without a basement and want to insulate the floor slab optimally. The house will probably be built with 42.5 cm aerated concrete. It is especially important to me that the insulation is well protected against thermal bridges.
Do you have any suggestions, experience, or expertise on this topic? Which materials and methods can you recommend to effectively insulate the floor slab?

I have read myself silly on the internet and have not become any wiser, as there is very little to find on the topic of KFW 40 and thermal bridges at the same time.

Recommendation from our contractors: insulation only above.

Thank you in advance for your help!

It is particularly important to me that the insulation is well protected against thermal bridges.

That applies to every new building. Whether it can be done slightly better and you save €1.25 heating costs per year with perfect optimization is another matter.

Recommendation from our contractors, insulation only above.

Then build it that way. Alternatively, your planner should come up with a proposal that perfectly fits your individual construction project.

Since we are building near railway tracks and a level crossing, we have repeatedly emphasized that we want to build with bricks for sound insulation and durability reasons, and not with aerated concrete. This question was completely ignored, and instead the answer was redirected to "You will get a KfW-40 house," with reference to aerated concrete 42.5.

We are planning a new build without a basement and want to insulate the floor slab optimally. The house will probably be built with 42.5 cm aerated concrete.

Do you now agree with the disregard of your request by a possible general contractor, or where does the change to his proposed wall structure come from?

The main problem is that this is our only option to build, as the plot is also being brokered through this licensee.

How economically sensible the desire to build without a basement is cannot be assessed without knowledge of the plot. I had understood it so that if the timely revocation is exercised, a plot would first have to be searched for again.

It is especially important to me that the insulation is well protected against thermal bridges. Do you have suggestions, experiences, or expertise on this topic? Which materials and methods can you recommend to insulate the floor slab effectively? I have read myself silly on the internet and have not become any wiser, since there is very little to find simultaneously on the topic of KFW 40 and thermal bridges. Recommendation from our contractors: insulation only above.

Which contractors exactly, and why do they advocate insulation only above? The exterior walls with insulation above the floor slab would hardly be under-insulated, I do not see how this would come any closer to a (why?) targeted EH40 standard than taking aerated concrete in caliber 365. Is a semi-detached house still planned with your own plot search?

We have a basement on a slope and KFW40 with 20cm XPS high compressive strength under the floor slab. Also with 42.5 cm bricks. Above the floor slab is no longer considered state-of-the-art according to many opinions.

We have a basement built into a slope with 20cm XPS high compressive strength under the floor slab according to KFW40 standards. Also with 42.5cm blocks. Above the floor slab, according to many opinions, this is no longer state of the art.

This has nothing to do with opinion or fashion. The walls stand on the floor slab; no insulation is placed between the floor slab and the wall. If there is no insulation under the floor slab, the temperatures of the room and the ground exchange through the floor slab as a conductor, and the floor slab also acts as a conductor of ground cold into the masonry. For the heat transfer through the masonry, this is equivalent to the effect of a wall with a lower thermal insulation value. Therefore my statement "masonry caliber 425 without insulation under the floor slab will no longer be adequate compared to masonry caliber 365 with insulation under the floor slab." A bicycle left next to the fence with only a lock instead of being chained is stolen quickly. Once the cold has penetrated the wall through the floor slab, insulation laid as a carpet in the room only benefits the room, but no longer the walls. Thermal insulation that is "a bit pregnant" is nonsense. And EH40 is supposed to be targeted here.