Is the total budget for the construction project realistic?

Yes, and we have tendered most trades individually. That would also have been significantly more expensive.

I find the total costs quite realistically estimated. The ancillary construction costs vary extremely, especially since the construction cost subsidies (which you have to pay) to the water and wastewater disposal providers can reach very high amounts. Perhaps these are already included in the development costs? If you are still looking for saving potential: Does it have to be a basement (flat plot)? Then better a few more square meters of area – although the plot size (without knowing the details) probably does not allow much more. Compared to many other "cost breakdowns" you are really at a good level there.

Thanks for the assessment. Do you mean realistic in the sense that the probability is high that we will even come in a bit under, or that it will just barely work out?

Yes, the basement. Of course, it can be discussed whether to just leave it out. But we would rather not do without it. Mainly because, as you already said, due to the building window, it will be difficult to compensate with more living space or other approaches like basement replacement areas in garages.

I would also consider it a reasonable, perhaps even somewhat generous estimate. It is important to be clear before signing with the general contractor / whatever about what you want and to price it correctly from the start. With constant 'upgrades' during the construction phase, you can really exceed any budget. You definitely have some leeway in the planning for a few extras / comfort features. You could break down the 125k incidental costs, that looks like a lot to me at first, although landscaping etc. naturally costs a lot if you have everything done. KFW 40+ should also be possible, but I don't see the point. In my opinion, the additional costs are better invested elsewhere. On the insanely expensive plot, I would definitely not do without the basement.

I would also consider it a reasonable, perhaps even somewhat generous estimate. The important thing is to be clear about what you want before signing with the general contractor / whatever and to price it correctly from the start. With constant 'upgrades' during the construction phase, you can easily exceed any budget. You definitely have some leeway in the planning for a few extras / comfort features. You could still break down the 125k incidental costs, that seems like a lot to me at first glance, although outdoor facilities etc. of course do cost a lot if you have everything done. KFW 40+ should also be possible, but I don't see the point. In my opinion, the additional costs are better invested elsewhere. On the ridiculously expensive plot, I would definitely not do without the basement.

Thanks also for your assessment.

So I don't actually have the exact breakdown on hand. Thanks to what I consider fair advice from a system builder, I thought we planned well and especially preferred to go by the motto a bit more rather than maybe really necessary. It definitely included:

- Utility connections
- Kitchen --> here we simply planned €20,000 for safety
- Single garage --> €18,000
- Permits and applications
- Outdoor facilities green and gray
- Fencing
- Preparatory earthworks for basement and other earthworks on the property
- Surveying of the property
- Provision for upscaling --> that was, I believe, €9,000-10,000
- What we hadn't considered so far were flooring and painting. I estimate around €15,000 - 20,000 if you don't opt for strip parquet flooring.

Now about the KfW 40 Plus standard. We just inspected a show house with ventilation system and cooling via underfloor heating. That already convinced us in terms of indoor climate. Especially as we so far also find the possibility of the KfW loan and repayment subsidy quite appealing.

The KfW loan is (if you do not get ridiculously bad conditions on the open market) unattractive both in terms of interest rates and conditions. Only the repayment grant can make it interesting IF you already meet the requirements anyway. Accepting additional costs for it is hardly ever sensible.

Ventilation system and underfloor cooling do not necessarily have anything to do with the efficiency class – we are getting ventilation (no cooling, but that does not matter here) and have only uncertified KfW55.

The KfW loan is (if you cannot otherwise get extremely bad conditions on the open market) neither attractive in terms of interest rates nor conditions. Only the repayment grant can make it interesting, IF you already meet the requirements anyway. Accepting additional costs for it is rarely sensible.

Ventilation systems and underfloor cooling do not necessarily have anything to do with the efficiency class - we are getting ventilation (not cooling, but that is irrelevant) and only have uncertified KfW55.

Have you calculated what the actual price difference would be between KfW 40+ and 55? Do you also have a photovoltaic system or a heat pump heating system?