New construction project - do you have any advice?

About our construction project:

- We want a single-family house with a granny flat (a two-family house is also possible).
The "main apartment" should have 4-5 rooms on about 120 m² and the
granny flat 3 rooms, spread over about 80 m².
- The plot is not yet available - we first wanted to see if the project is
feasible.
- A new building is planned in the Stuttgart area, radius about 40 km.
- Budget: All together about €350,000 up to a maximum of €500,000.
- Expectations are quite solid, we don’t need any "frills" - 4 walls, a roof, garage and storage options (whether in the basement or a separate room does not matter).
The price-performance ratio should simply be right.
- Cost breakdown: Building plot about €120,000 - incidental costs €40,000 - garden €10,000 - garage €7,000 - kitchens €20,000. The remaining budget is then intended for our house.

Now to our questions:

1. Is the project feasible at all with the budget? What amount should we otherwise expect in this
range?

In the Stuttgart area, it will be difficult to get a building plot at your price. I know the area very well and estimate land prices at about €300/sqm.
Are the €120,000 already including all additional costs? That is 5% tax, 3.57% broker, 2% notary and land registry?
The garden is also optimistic, but it can be finished later… I also include driveway and terrace in that.
Garage €7,000 if it is a 3x6 standard garage.
That leaves you €300,000 for building the house. Without a basement, I’d say that’s doable. With a basement, which can easily cost €40,000 or more, it gets tight.

[/I]400 sqm plot "could" already be rather tight - rather less suitable for a two-family house, but for a single-family house with a granny flat, yes. If in the latter variant the granny flat is supposed to be 80 sqm, there is not much space left for kitchen and living room on the ground floor of the main apartment; so better decide on a two-family house or make the granny flat smaller.

Additional construction costs of about €35,000 are realistic (if the plot does not entail additional foundation costs) - however, these costs do not include painter work or floor coverings; also, the outdoor facilities and access paths come on top. Allocating €10,000 for outdoor facilities is fine, that covers some small trees and turf; in my opinion enough for the beginning. For a terrace, you should calculate €60.00, for the access path about €55.00 per square meter.

A solidly constructed two-family house of the desired size is feasible for about €300,000 including basement - however, as a pure energy saving ordinance house. For KfW 70 you have to spend another good €25,000 (insulation, more technology). Consider extras such as electric shutters etc. - so rather base your calculation on €300,000 for a house on a slab.

A prefabricated garage 3 x 6 is also available for about €7,000, even with an electric sectional door. You will probably have to provide 4 parking spaces.

2. Classic topic: wood or stone? Generally, we are open and unbiased towards both building materials.
We are also aware that both building materials have advantages and disadvantages.
In the meantime, however, we have been overwhelmed with many, partly contradictory opinions/views.
a) Is it, for example, true that "wood houses" are 3 times more durable than "stone houses" and also
offer better fire protection?
Wood usually burns much better than stone :) Regarding fire protection, I would rate both equally because fire-retardant materials have to be used anyway. But ultimately, when it burns, every house suffers.
Well, for durability, one cannot say; there are 30-year-old stone quarry shacks and well-preserved 100-year-old houses. It’s all a question of care and maintenance.
Our house provider has been building houses in timber frame construction for 60 years, and some of them still stand today. The question is rather: do you want to live in a house with today's standard in 50 years? Do you know how technology will change? I think building houses for generations is no longer so profitable today… the children tear it down anyway and build something new :)
All advertising blabber – qualitatively high-quality timber houses are not less durable than their massive counterparts. And – if a stone house burns, only the walls remain – whether these can be found again in a new building, I strongly doubt.

b) Is it true that sound insulation is significantly worse in "wood houses" than in "stone houses"?
Depends on the workmanship and quality.
No.

c) One provider also said that a "wood house" is just as stable and "holds up just as much" as a "stone house". Is this correct?
These Californian plank shacks certainly not, but a solid wood house definitely… the Swedes and Norwegians almost exclusively build like this, it can’t be that bad.
Yes.

d) What do you know about the resale value of the two building methods? We have read several times
that when selling a "wood house" you have to expect a loss of value of up to 40%.
There are real clairvoyants among the sellers. If you plan to sell, build with stone, because the prejudices against wood will not be removed from people’s minds so quickly. In my opinion, the resale value is only affected by the location of the plot. Especially in the Stuttgart area, where space is really scarce.
It depends decisively on the provider you choose. Generally, it is true that banks apply a lower lending limit for prefabricated houses. On resale, it is then like everything else: the market regulates supply.

e) Is it true that the two building materials cost similarly at a comparable quality standard?
Our talks have shown… yup. If you build cheaply, don’t be surprised later.
A qualitatively high-quality prefabricated or timber house is generally more expensive than a massively constructed single-family house. It has to be, as the effort from production to erection is quite different.

3. Are cheaper construction companies automatically of lower quality than expensive ones? Do you know
reliable and high-quality construction companies that also stay within our budget?
You always have to consider how and why they can offer cheaper prices. Either they pay their people badly, or they always use the cheapest building materials. Or the bill is inflated later by "additional services" and excessive surcharges. Or it’s the insolvency model :)
Cheap is always relative. If you have a provider who underbids other comparable providers by more than €5,000 to €8,000, you should be careful. Because cheap is always actually quite expensive in the end.

5. Is our rough cost breakdown (above) somewhat realistic?
Roughly yes. We are building a prefabricated house without a basement of about 140 sqm for €215,000 + incidental costs. A colleague of mine built a two-family house for just over €330,000 with a habitable basement

Yes.

6. What do you think about automatic ventilation? Is it recommended for both building methods
(wood/stone) or have you had bad experiences with it?
I would not build without it… especially in massively insulated houses, everything is completely sealed. If ventilated incorrectly, mold is guaranteed regardless of building method.
Financially and heating-wise, the systems are not worthwhile, but they certainly add to living comfort. Costs about €7,000 - 10,000

I always recommend installing ventilation, if you choose a prefabricated house even more so. All houses are built so tightly that mold finds optimal conditions. Even if the system may not pay off, it spares you from mold and provides you with a mostly pleasant indoor climate.

my answers in blue