Is the financing volume for our construction project realistic?

as it all reads, no big DIYer is planning here.

Yes, I thought so while reading too ;)

I see ongoing costs for garden maintenance,

Ride-on mower..

I have no problem mowing the lawn on weekends. We might also plant a few trees, but I wanted to look into that more closely,

Orchard meadow would probably be ideal. Also provides food for the rented horse :)

The grandparents want to donate a wooden play tower with slide and swing, that will then reduce the lawn area a bit.

That doesn’t reduce lawn area, since the play equipment stands on lawn. It just makes mowing a bit more complicated.

Regarding the question: certainly building the house and the financing is doable, but what shouldn’t be forgotten are the bills that most homeowners skip because they do it themselves. As also pointed out: it reads as if all work is outsourced. That adds up monthly, especially after building the house, no one just pays a hundred-euro bill anymore. The additional costs will probably have to include a gardener service?! And just like that, such a large salary quickly melts away.

By the way, I just came up with an idea for the shed: alpacas or sheep as lawn mowers :)

It always makes me very skeptical when someone whose profession is "managing director" asks third parties for an assessment of (his) (admittedly largest) private investment.

How do you make decisions in your professional life?

For me, this request is an indicator that the project is giving you a headache and you consider it too big a deal. If a few people write here "with your income, you can build a nice little house," your feeling will only improve temporarily. The doubts will catch up with you again at some point.

Why does it have to be such a huge plot and a pool? If you have 3 children and you work a minimum 50-hour week... who then takes care of the garden on weekends? It ends up being a gardener who wants his 300-400€ per month...

With your income/expense situation, of course, you can build. But maybe just a bit smaller for peace of mind. My tip would be: less land (possibly split into two or three plots) and leave out the luxury pool for now (you can still treat yourself to that after a few years). That way your project is already 200k cheaper...

I understand. Our 15,000 euros are meant solely for a different bathtub, a larger washbasin, more sockets, network cabling and such things within the house.

A small example from our single-family house planning. We have decided on the following upgrades in the last four weeks alone, deviating from the original budget:
- a smart home (entry-level) system based on radio (approx. +3k)
- wood-aluminum instead of plastic windows (approx. +4.5k)
- Dornbracht fittings in all bathrooms (+15k).

And that even though we had already budgeted for a higher-end standard of execution in advance.

I’ll just say it outright now (even though I believe in a credible financing, amount doesn’t matter for my concerns right now): I find the calculations partly quite confusing and overly optimistic.
Firstly, regarding the existing salary:

The reflex is of course also with us “full-time with three small children - no chance,” however, for some months it at least worked well with two small children.

What incomes do you have (gross/net)? approx. 9,100 euros net per month including child benefit and approx. 10,000 - 25,000 euros net variable components per year.

[*]Total income: currently approx. 7,500 euros
[*]Total expenses: currently approx. 4,500 euros
[*]Balance +3,000 euros

[*]Total income: approx. 9,100 euros
[*]Expenses with three children then total: approx. 2,500 euros living costs and 500 euros ancillary costs
[*]Balance +6,100 euros
[*]From this the loan installment would then have to be deducted, we would like to aim for around 3,000 euros installment per month. That would then be a balance of about +3,100 euros per month.

Sometimes it’s about 9,100 €, sometimes “only” 7,500 €.
Let’s not kid ourselves: even despite daycare and school, you still need a part-time caregiver who doesn’t switch between home office and three children and ultimately doesn’t do justice to any of that - the kids get too little attention, work suffers, and you no longer have a hairstyle... so time for yourself. My personal opinion is that with two children you should reflect inwardly about which role you really want to embrace for yourself. And possibly take a step back professionally (kudos to women who have the choice), which basically isn’t relevant here.

Then the ancillary costs, which are quite high or higher in a house, including risk insurance and building insurance.

The ancillary costs are quite high, but these include costs that will later fall away (full winter service, gardener for the front yard and hedge trimming).

I don’t know anyone who gives up winter service and hedge trimming, but these jobs are rather part of a single-family house than in a rental situation. So they do not disappear,

if you subtract the current cold rent and another 50 euros for gardener and winter service from the costs,

here again...

[*]Outdoor facilities/terrace, paths, garden design, fences etc... estimate 170,000 euros including garage, carport element, terrace, fences, etc.
[*]Total costs approx. 1,050,000 euros

Most builders swallow this and do a lot of these things themselves: garden: own work, paths: own work... if I had arranged our garden through a service provider, I’d probably be 30,000 euros poorer, for some shrubs on a garden area of 300 sqm plus front garden beds.

Then recurring items:

Furniture, lamps, decoration: we will mainly plan a new dining table with chairs, otherwise we hardly need any furniture. We would do this from the current salary and not finance it.

I do this from my current salary though

When the interest rates for the house construction become due and rent still has to be paid, then even a high salary of - let’s calculate realistically 7,500 € - becomes tight.
The same applies to special payments:

For this we also want to contribute 5,000 - 10,000 euros p.a. from our special payments.

[*]I do not calculate costs like insurance or vacation, I rather offset these with the annual special payments

Just think about the placeholders “full-time wife,” recurring items, special payments and own work or the question: who takes care of your daily house + garden work?
The garden is more than watering and mowing... housework has to go on, too... service providers?

And when I consider that we have already spent upgrade costs of about 40,000 € in our small single-family house just for sanitary, flooring and modest design things, I wonder how your 15,000 € buffer is to be assessed.

Fact would be, I’d say, that you are well positioned with 7,500 € and equity of 140,000(?), but I don’t see such wishes as a pool or extravagances like dozens of service providers if you assume a plot of 300,000 € and a 200 sqm house.

These may be desires you treat yourself to at some point when you have survived the acquisition phases after 5 years.

Our 15,000 euros are purely intended within the house for a different bathtub, a larger washbasin, more sockets, network cabling, and such things.

I can confidentially tell you that in our case the 15,000 EUR is used exclusively for the sanitary items you mentioned (bathtub, toilets, washbasins, fittings) including installation. However, we are still missing around 10,000 EUR for bathroom furniture. For additional sockets and network cabling alone, I would estimate about 5 - 10 K, unless you belong to the faction "network once in every living room." And as I wrote above: For our buffer for the earthworks (10,000 EUR), we had to calculate double again. It's not like we didn't calculate a buffer from the start. ;)

I'll just say it outright now (even though I believe in credible financing, the amount is irrelevant for my concerns for now): I find the calculations partly quite confusing and overly optimistic. For one, regarding the existing salary: Sometimes it’s about €9,100, then again "only" €7,500. Let's be honest: even with daycare and school, you still need a part-time caregiver who doesn’t switch between home office and three kids and ultimately fails to fully meet either—kids get shortchanged, work is neglected, and there’s no more hairstyling... so time for yourself is gone. My personal opinion is that from two children onwards, one should reflect on which role to really embody for oneself and perhaps reduce working hours in the professional world (kudos to women who can make that choice), but that actually doesn’t matter here. Then the ancillary costs, which are also quite high or higher in a house, including risk insurance and building insurance. I don’t know anyone who delegates winter service and hedge trimming, but these tasks occur more in a single-family home than in a rental. So they don’t just disappear. Here again... Most builders swallow it and do many things themselves: Garden: do-it-yourself, paths: do-it-yourself... if I had had our garden installed by a service provider, I’d probably be €30,000 poorer for some shrubs on a garden area of 300 sqm plus front garden beds. Then ongoing expenses: When the interest on the house construction is due and the rent still needs to be paid, even a high salary—let’s realistically say €7,500—becomes tight. The same applies for special payments: Just think about placeholders like "wife full-time," ongoing expenses, special payments, and own contributions or the question: Who manages your daily house+garden work? Gardening is more than watering and mowing... housework has to get done too... service providers? And when I consider that we have already spent upgrade costs of about €40,000 on just sanitary installations, flooring, and modest design items in our small single-family home, I wonder how to assess your €15,000 buffer. The fact is, I would say you are well off with €7,500 and equity of €140,000 (?), but I don't see wishes like a pool or extravagances like numerous service providers if you assume a plot of €300,000 and a 200 sqm house. Those may be wishes one allows oneself eventually, after surviving the acquisition phases for five years.

I think these are great points. I didn't want to start a fundamental discussion. A managing director surely has a few hours to scrub as well. I’m now working from home and working more, with kids breathing down my neck, the small garden, and a bit of sport one also wants to do. But please not between 6 and 7 pm because that’s family dinner time. I think life around it is often underestimated. Of course, there is childcare, grandparents, and also service providers, but that’s not my thing. I prefer smaller but finer.

Those are good points, and this exact "mirror" is what matters to me, it is our first and hopefully only house. I also know the saying enemy, friend, etc... ;) So an honest thank you for all the assessments.

The salary is simply explained, together with child benefits we earn 9,100 euros, in the next twelve months the amount will drop to 7,500 euros due to one year of parental leave and then rise again to the previous amount. With three children we logically have no experience yet and are absolutely open to reducing hours so that the children have a good life. That is why it is important to us that financing is permanently no problem even with the mentioned 7,500 euros.

Regarding the aspect of doing it yourself and own contribution, we are completely open to it, but in the cost calculation we deliberately calculate as if the entire house with outdoor facilities is carried out by companies. The thought "a lot of work and child care" plays a role here, especially because I already think that some people make the financing look better by assuming 50% own contribution, which then might not work out. I see this as a kind of risk buffer, I plan with full external service and would then still have leeway to say, for example, that we do the garden fence, lawn and possibly painting work, terrace and other paving work ourselves. This is currently by no means laziness, but financial caution.

We have been living for several years in rented houses with gardens, there was also a garden almost the size of our new plot. Therefore we have realistic experience values for ongoing maintenance, which is easier than if you have always lived in apartments before and cannot estimate the garden topic well. So far we have always shoveled snow ourselves and taken care of the hedges, but there was no choice at our current home. Therefore I conservatively calculate 50 euros from the very high additional costs again because in the new house I will certainly not order a gardener and will shovel snow myself. We also do not plan with rose beds or similar, but mainly relatively lean with hedge and lawn. Regarding time expenditure, I have no worries, it is manageable on weekends and perfectly fine for us. Maybe in a few years I can afford a Farmbot... ;)

K1300S’s experience already worries me a bit, because besides the pure house price that is probably the point I can least grasp. In the first offer I do see surcharges of almost 1,000 euros each for three tiled showers, but the feeling for standard vs. upgrades is otherwise quite diffuse. Therefore I now mention in every initial conversation that I consider a preliminary sampling necessary to get a better impression. However, almost all companies are very reserved about this, those with sampling centers typically stall with vague references to Corona, the others with decentralized trading partners generally fumble a bit. I have to stay on it.