Planning of a single-family house (basement + ground floor + upper floor) on a 480m² plot

Many thanks again for all the helpful answers. The forum is really great and I have already been able to learn a lot from you :)

On the topic of ventilation system: I will take a closer look at that.

On the topic of heating & solar thermal & photovoltaics: I am still quite clueless here. The only thing I am almost certain about is that natural gas is out. Everything else I still don’t know... Air heat pump? Geothermal energy? With solar thermal? Photovoltaic system? With storage or without, or not at all? Everyone recommends something different...

On the topic of sauna: that’s true, having it on the upper floor with balcony access is really a great thing and you save the cost of an additional bathroom. Yes, I would somehow make it privacy shielded. Question to @Würfel, how many m² is your bathroom on the upper floor with sauna?

On the topic of fitness: I see it the same way as Würfel, for me it’s also about the heat development. I would still see it in the basement. Also a question to Würfel, how many m² is your fitness area in the basement?

oh yes and of course the most important topic financing and budget: with the one I mentioned, there is still a bit of leeway, but I want to stay under 900k. But that also includes own work (planned are floors and painting work and the entire garden as own work) and moreover you could cut a few things here and there that are not important - for example the carport can be left out for now and just a gravel parking area instead. But yes, I still have to do a proper budget planning. Unfortunately, we don’t have much equity that we can raise, but we earn well and that should make it doable.

: definitely, the plan will be posted here in the next few days :)

Oh, and one more thing, because it was mentioned here that I probably live in an old building now. No, I currently rent a KFW55 house built in 2020 with 46er (?) walls, so everything is sealed and without a ventilation system. I never get the feeling that the air is so bad that it can't be exchanged with a few minutes of airing out. But as I said – I still need to take a closer look at the topic of LÜftung.

@11ant: you wrote again about the stairs, I really have to reconsider that. We can also push the building envelope a bit more and make the house a little bigger, maybe that would be better for the straight stairs (or they just get omitted, it’s not a MUST).

I would N.E.V.E.R inflate a house for the purpose of presenting a staircase. No man can be that beautiful (sang Gitte) :)

Oh, and one more thing, because it was mentioned here that I probably live in an old building now. No, I currently rent a KFW55 house built in 2020 with 46er (?) walls, so everything is sealed and without a ventilation system. I never have the feeling that the air is so bad that it can't be replaced by ventilating for a few minutes. But as I said – I still need to look more closely at the topic of ventilation.

Check if window rebate ventilation is installed. I would at least use that for a new build being rented out.

Yes, in my condo there is, for example, Regelair installed and a fan in the bathroom regularly starts at a very low speed to create the necessary negative pressure. Unfortunately, it is not quite enough for the [Pumakäfig] in my case. I’ll have to take another look at the fans...

Don't want to just harp on the budget, but your 900 also wobbles there.

For example, my estimate is missing the architect (around 50k). Also, no buffer included yet. And since you are just starting to plan... add 5-10% price increase until you get that far.

And just so you know... integrating a sauna into a bathroom... if we are not talking about a hardware store infrared cabin here... you're immediately looking at an additional 10-15k upwards...

You already said the carport can come later, etc... and you can do some things yourself. But don't overestimate that. Material still costs... and especially for the outdoor facilities (is retaining necessary?).

Regarding the budget, take a look here as well