Insulation under the floor slab - Is it sensible? Experiences

I leave everything as in the original with the 100 mm Styrodur, it will become even better than KFW 40 but I will never know exactly how much (because a new thermal insulation certificate would have to be created, which no one does for free) and I probably will never notice savings in heating costs because the comparison is missing....

If it doesn't hurt you financially, then leave the insulation as it is. However, the savings on heating will be so small that you will not notice a real difference compared to the variant without insulation. BUT: you have a house that will be more interesting to potential buyers than others in the future. KfW subsidies can also play a role. It's a numbers game (rather subjective).

I also consider insulation below the BP absolutely necessary given the valid EEV guidelines and the foreseeable development in [DL].

I myself intend to insulate below the BP with 30 cm XPS, without a slow-responding underfloor heating system. It will be a bungalow in timber frame construction according to passive house standards, with oak parquet flooring everywhere, heated mainly by solar radiation; if needed, by wood stove and/or mobile infrared convectors. Domestic hot water production will be done using modern instantaneous water heaters directly at the points of use.

Result: minimal investment costs, no heat losses in pipework, no heat losses in water storage; neither for heating water nor for domestic hot water. Those who can calculate here have a clear advantage.

Heating primarily by solar radiation; if needed, by wood stove and/or mobile infrared convectors.

So from October to March the stove is on?

Result: minimal investment costs, no heat loss in pipelines, no heat loss in water tanks; neither for heating water nor for hot water. Those who can calculate here are clearly at an advantage.

We have implemented it similarly. I cannot confirm minimal investment. A proper masonry heater also costs a lot.

So the stove is on from October to March?

Oh, from October to March the sun doesn't seem to shine where you live? Where do you live?

We implemented it similarly. I cannot confirm minimal investment. A proper masonry heater also costs a fair amount.

In my opinion, a masonry heater is not necessary in a passive house with a timber frame construction. On the contrary, the single-story house even tends to overheat quite quickly with it. Therefore, I also do not need any thermal mass in the wood stove. And besides: How many masonry heaters could I probably buy for the costs saved by not installing a heat pump?