House price okay? KFW 55, 190 sqm, without basement

We are planning to build a 190 sqm single-family house according to Kfw55 standard in northern Lower Saxony. The shape of the house is relatively simple: gable roof with a protruding living room and a roof over the recessed area. One-story construction, 131 m² base slab, 1.6 m knee wall. Engobed clay bricks will be used, 24 cm mineral wool insulation for the roof and top intermediate ceiling, knee wall for inside walls top and bottom, knee wall for exterior walls, 16 cm mineral wool insulation, fully brick-faced (65 cents / brick). Tiles will be laid throughout the house (tile price €25 / sqm), roller shutters with belt drive everywhere, painting work up to €6K, decentralized controlled residential ventilation with heat recovery. Interior doors are budgeted at €240 including fittings. 43 m² window area. Gypsum plaster (but we probably want to change that). Adequate electrical installation. Basically, we just hope it will be robust. The offer does not include sand slab, water supply or drainage lines, earthworks, heating or sanitary fixtures. The offer is €233K. Another offer is now available for sanitary and heating. This includes: sanitary for one WC, one shower bathroom and one bathtub and shower bathroom (8 m²), underfloor heating with 15 cm laying distance (we had read that 10 cm would be better or even better to consider the whole thing more differentiated), heat probe drilling, 2 water connections for the garden (we had not requested this, but why not), 300 L tank (I still have to check if that makes sense, since the device actually already has a tank inside), supply and drainage lines in the house. The sanitary fixtures are also rather "robust" - the most expensive will probably be the bathtub (Kaldewei Mega Duo 180 x 90). The whole thing is supposed to cost €48K. We would like to build with the general contractor since he is local and has been recommended to us twice already - but we would still like to estimate whether the offer is okay, we are a bit unsure about the heating company.

About 1500 euros/m² with the included services I find acceptable.

Good evening,

Just under 1500 euros/m² with the included services I find acceptable.

That is exactly what I don’t quite get; for a KfW 55 efficiency house with the described services including plumbing/heating, it is in my opinion too little; also for Lower Saxony... but I may be mistaken.

Rhenish greetings from on the road

As said, all additional costs, sand slab, sewage and water supply lines, construction electricity and water are still missing, the RDK is also unclear (according to static "only" 1400 kg/m³), it is unclear how many decentralized ventilation units. Sanitary will probably be even more expensive - we are rather skeptical of 15 cm installation spacing and plastic drinking water pipes. But we are glad that it seems to be a fair offer.

Offers from Viebrockhaus or Elma were actually even cheaper back then.

It's also fairly inexpensive, but conceivable in northern Lower Saxony (between Emden and CUX).

I'm currently surprised by the separation of the ventilation system and heating. I only know decentralized ventilation with heat recovery from IWS, where the exhaust air of the boiler is fed and processed in the heating circuit. But then it would have to be a system...

Brickwork up to 65 cents is certainly a fair price category, usually you only see half of that. In general, this actually shouldn't be included at this price yet. With a 1.6m knee wall, that already results in a few square meters of brick surface overall.
How does the processing look? Rolling layers in the windows, or aluminum window sills? Vertical or horizontal lintels simply built through? Corners or bullnose bricks? Flush pointing or separate jointing?

But even if something extra is added here and there, this is a reasonable price. Serious evaluation is only possible with a scope of services description.

Window sills as a screed layer and joints subsequently grouted gray. We still want to ask whether there is a Grenadiers layer, as well as about the corner masonry. The ventilation consists simply of holes in the wall with an inverter PC fan and ceramic housing for heat recovery – we saw this with another client and actually thought it was quite okay. The performance specification is still somewhat vague in some places – for example, it says "160 mm core insulation" but not what material. We strongly assume it is mineral wool, as the builder has always mentioned that so far.