Floor plan design single-family house on a slope, granny flat, double garage

Basement apartment out. Open space downstairs.
Practice room in the garage or under the garage. Redesign.

At least remove the stairs, outside stairs so it looks a bit smaller.
Pantry on the ground floor out. There is the basement for that.
The mini office upstairs.
Be sure to draw all rooms with existing or desired furniture, including the practice room, to scale. That way you’ll quickly notice if the books or workbench fit. Size isn’t everything. When it comes to tables, make sure to allow at least 80 cm of space from the table edge.

That looks quite nice, authentic like a 1950s suburban house with an extension, raised by about a knee wall during modernization, and so on. Nice, but a shame about it: you will have to plan completely anew, preferably with an independent architect. Teachers' children and the pastor's livestock rarely or never succeed: in my opinion, the "design technique" of "retrofitting" a 10 sqm budget overrun per floor in a "finished" design is almost hopeless.

Phew, I have already deleted this dozens of times because I think it’s not working. I don’t want to harp on your numbers, own contributions, equity, or whatever. You’re not the only one who thinks they can save one-third of the house construction costs with an excavator and muscle power through various friends and relatives.

Browsing the internet gives me numbers, including the 350€/m3 (no annual source, but a report refers to a source from 2017, though I have also read 800€ for higher-end standards...), figures from the Federal Statistical Office, which you can’t really trust anyway because the survey is based on information from builders who want to reduce their land acquisition costs as much as possible) so nicely adjusted downwards, but also numbers from the alleged future 2021, where 2000€/m2 is estimated. And since one wants to cite a reliable source, I rummaged out my building application (unfortunately only from 2013) and photographed the relevant passage. It’s a normal house (cheap construction area in northern Lower Saxony), 135 sqm, gas heating Energy Saving Ordinance 70, plaster facade, average equipment. The construction service description is slightly better than Heinz von Heiden. Construction costs* come to 200,000€ without surcharges for floor coverings and expensive frills. *without land, garage, outdoor facilities, slope, and without additional construction costs!!!

[ATTACH alt="IMG_0122.jpeg" type="full"]58805[/ATTACH]
[ATTACH alt="Bildschirmfoto 2021-03-15 um 17.26.57.png" type="full"]58806[/ATTACH]Source: Federal Statistical Office, left construction year, middle cost/m3, right cost/m2

Facts:
2013 [B][U]429€/m3 1500€/m2 466m3 x 429€ = approx. 199,000€ or 135m2 x 1500€ = approx. 202,000€[/U][/B]
According to the Federal Statistical Office, my m2 value is quite good within the norm, but not the m3. I would have to add (somewhat more than) 1/2 on top of that. What would my house cost today? Simple rough calculation, rather conservatively estimated:

2020 (350 + 1/2) 525€/m3 1900€/m2........466m3 x 525€ = approx. 245,000€ or 135m2 x 1900€ = approx. 255,000€
2021 (360 + 1/2) 540€/m3 2000€/m2.......466m3 x 540€ = approx. 250,000€ or 135m2 x 2000€ = approx. 270,000€
These are the guideline values for my house.

Where do we find you/your house?

KFW 55 house
Residential building: 1,145.917 m³ x 350 €/m³ = 401,070.95 €
Garage: 511.66 m³ x 175 €/m³ = 89,541.55 €
Additional construction costs: 30,000 €

260 m2 living area

2021 540€/m3 2000€/m2......1145m3 x 540€ = approx. 618,000€ or 260m2 x 2000€ = approx. 520,000€
without garage, Energy Saving Ordinance 70, plaster facade, without slope reinforcements, without additional construction costs. Although I would also raise the price per sqm somewhat, to about 550,000€, because in a basement apartment technology and sanitary, the cost drivers, have to be provided twice.

And whoever tries to sell you the fairy tale of the big house with basement apartment for 400,000€ (own contributions etc. don’t matter at this point) belongs in jail. Your ears should already be ringing if you compare the garage at 90,000€ to a three-story finished residential building at 400,000€. The 350€/m3 figures are from 2010 or apply to a shell house!

Based on this simple calculation, only this can be said:

Basement apartment out. Open plan down.
Practice in or under the garage. Redesign.

Anything else would be negligent.

P.S. Personally, I am glad to finally have found a reason and to have done this calculation for my little house.

My question about the age of the architect probably hit the mark. Not only regarding the budget.

Perhaps a certain age - that is: life experience - is indeed required for such (construction) projects? Wasn't there recently a couple in their early/mid 20s with rosy (price) expectations and the belief that 180 sqm is the existential minimum living space?

Price estimate according to architect/planner only house: 410k€
Personal price limit for the house, including equipment: 320k€ / Deduction kfw 2 residential units each 25600€

You can already see the difference.

I’ll ask just to be sure: Is it allowed to run a business in your two-family house in that building area?

Also, in my opinion, KfW funding does not apply to business?

Where are the parking spaces for the 2nd residential unit? And/or those for the business?

I just hope you don’t get a loan from the bank. Otherwise, there will soon be one more shell on the market.

In my neighborhood, someone also runs a massage practice on the ground floor. They live upstairs in the attic. That can financially work for you too. Only on a slope, that only works if you omit the roof and the garage or at least convert it into a carport.