Budget planning for second house construction - experiences

We would like to build rurally again in BaWü (Biberach district).

Our 2008 timber frame house built to the good insulation standards of the time, with good equipment and move-in ready condition including a great garden, is to be sold.

That means we "unfortunately" have a few requirements for a new potential home.

Specific requirements:
Separate children's area with an additional bathroom
Smart home solution (e.g. Loxone) in minimal configuration
Flat roof (flat roof or shallow pitched roof)
Passive house construction (whether solid stone or solid wood depends on the price)
Photovoltaic system on the roof again (pays for itself)
Of course, we are calculating naturally and the bank has already advised us what would be financially feasible and sensible without any problems.

Since we built in 2008, we are certainly not used to today's construction prices :-(

If it is a hillside plot, then as small as possible, with the children's area in the slope with access to the garden.
If a flat plot, then everything should be on one level.

Our rough calculation:
€80,000-100,000 purchase of building plot (already developed):
€5,500-6,500 property transfer tax 5% + notary fees:
€15,000-20,000 architect (planning, applications, preferably knowledge notification procedure)
€25,000-35,000 earthworks, excavation, sewerage:
€4,000 electricity, telephone, water:
€35,000-45,000 landscaping:
Ancillary costs thus about €78,000 - 93,000
House (without basement) + attic + separate children's area
Passive house construction, triple glazing, blinds/shutters, mini smart home solution (only blinds/shutters, a few lights) Loxone with KNX switches.
Wooden floor, underfloor heating, brine heat pump with trench collector/ground collector
1x children's bathroom, 1x parents' bathroom, 1x guest WC
Possibly flat roof with invisible slight roof pitch, or very shallow pitched roof
Turnkey
+ double garage and partial basement
(only Loxone programming, KNX parametrization done by ourselves)
€2,500 per sqm, envisaged 160 - 180 sqm -> (€400,000-450,000)

Total thus somewhere around €550,000 - good €600,000 (Crazy!?)
+ photovoltaic system up to 7kWp (€8,400 net)

Do you have any points missing from our calculation, or not fitting at all, or are the prices still below current prices?

We want to have as realistic a budget plan as possible in advance. Of course, the purchase plot also has an influence on this.

Since we have no building obligation, we want to plan everything concretely. If it is not achievable within the budget, then so be it. Then we will stay in our house.

Many thanks in advance f

Stupid question, why necessarily a passive house?
The KfW loans are no longer worth it, as far as I know.

An acquaintance of ours built around 2005, 36.5 Poroton with WWWP. Heating costs about 40 euros per month.
If you build with a wooden frame, of course you can do that, but with solid construction it’s definitely not worth it.

Since you built in 2008, you are also not used to the sale prices.

I want to strongly question Passive House and photovoltaic system, neither of which easily pay off today. The plot of land seems to me to be priced tightly for your area. 2500 euros/sqm should be enough for a good standard, but I would rather assume 200 sqm for your requirements.

Do you already have the building plot (secured)? I find the price set very low. For 400-450K, you can build a house with "normal" features quite well. With your extra wishes [Kinderbad], [Passivhaus], [Smarthome], it will be quite tight, I think.

Yes, that won't work like that.....even if you should get a plot of land from the municipality because you are a local, in BW they already call up 180 euros per sqm....

For the house, I would rather calculate 550, if you don't want to do a lot of the work yourself, and I think that even then the brine heat pump with trench collector/ground collector isn't financially covered yet....

However, it should be noted: you will get a lot of money for your existing house! Just go to a real estate agent and inquire, or look at comparable properties in the listings.....you will be amazed. Don't ask the bank, they always estimate it too low.

Therefore, it could still work out after all, even if the construction is more expensive than you assumed

Since I come from the same district, I can confirm that the plot price is quite realistic (unless you specifically want to build in Biberach itself)... There are still villages and smaller towns here where you pay less than €100 per m², but without living completely in the countryside without infrastructure.

Given your requirements, I would also expect a bit more m². It also strongly depends on the details. The prices mentioned are realistic. The biggest risk that it won’t be enough is yourselves.
Passive house standard: build and insulate sensibly. Do not orient yourself according to any KFW regulations. It’s not worth it and is sometimes insane in detail.
Brine heat pump: calculate it yourself, we wanted a deep drill and no matter how I calculated it, it was really insanely expensive in the end.
Architect fees: I would see them rather in the double range, especially if you also have construction supervision, etc... Just google the HOAI calculator here...
And fundamentally, it’s always a question of the standard. You can live with €20/m² tiles, but also install €300/m² mosaic...