Floor construction new build single-family house kfW55

If you build a KFW55 house, you need a specialist consultant - you can't calculate it yourself.

That is clear to me. I am just doing rough calculations here so that I understand it a little.

I am building a prefabricated house and they also do all the calculations for the KFW, etc.

Since there was a change on 01.04., I was told that the perimeter insulation is no longer necessarily required to reach the KfW55 standard. As a compensation, there is then the 025 insulation under the screed.
This was implemented and a new energy saving regulation calculation was created, and it states 0.268 W/m²K for the floor. I do not know how high the value would have been before with the perimeter insulation (160mm).
The question is "only": Is a U-value for a floor slab against the ground of 0.268 W/m²K too high for a house that is supposed to be heated with an exhaust air heat pump?
If that should be the case, I would have to try to increase the insulation. According to the manufacturer, a buildup of the 025 insulation is not possible because of the anchoring of wall elements and such.
Thanks for the help

You are aware that the change means a TIGHTENING of the requirements. It does not mean that you need to insulate less!!!

I would NOT heat a KFW 55 house, where you also save on insulation, with an exhaust air heat pump. The risk that I would have to heat expensively with electricity in winter would be too high for me...

P.S. You are buying a KfW 55 house. Why are you now trying so hard to tell the professionals how to achieve KfW 55? There are many ways to get there.

nordanney, at the moment the tightening means that an electric heating has a greater positive influence on the calculation than before, so it is easier to meet the kfW requirements when using electric heating.

I am not trying anything here at all. I was surprised that after the change, which did NOT come from me but from them, the U-value of the floor is so high compared to all others, and my question is, as written in the first post, whether this value is too high for the exhaust air heat pump.
The suggestion to omit it came from the house seller, because according to him 8cm of the 16cm perimeter insulation no longer have any influence. Why shouldn’t I agree if it also becomes cheaper for me? Nevertheless, I am allowed to wonder why suddenly the value is so high and why I shouldn’t have stayed with the previous one.

The question remains how big a difference between 0.268 and 0.204 really is. Not only a cost question, but also an energy loss question. That is 0.64W/m²K at 100m² and 20° difference, so 1280 watts, at 20 cents per kWh a difference of 2242€ per year. Can that really be? If I calculate correctly, why am I being given such a suggestion that pays off within one year?

What would be a good U-value for a floor slab?

I assume that they know what they are doing, I was just surprised and so of course I try to inform myself.
So far, however, I have not received any useful answer, only posts saying that I insulate less, but according to the specialist advisor’s suggestion, so something is not right here.

In short: U-value 0.268 W/m²K too high?

0.06 more - You miscalculated slightly. Also in relation to the costs

oh You're right BUT ^^ 0.064W/m²K * 0.2€ * 24h * 365d * 0.001 * 20K * 100m² = 224.56€ so only the comma was shifted Then it looks different again, but there is still no information about whether it actually presents that way.
Sebastian, for example, what U-value do you have against the floor?