ᐅ Single-family house converted for two families: experiences with floor-by-floor separation?
Created on: 8 Apr 2026 07:45
M
mmyellow
Hello everyone,
We are currently at the beginning of a construction project in Ludwigsburg (Sonnenberg South-West development area) and would like to gather early feedback on the choice of plot and the overall concept.
The plots are allocated through an application process (up to 3 preferences possible, selection not guaranteed). We currently have 4 possible plots shortlisted and need to prioritize them.
Development Plan / Restrictions
Plot size: approx. 440 – 525 m² (4730 – 5650 sq ft)
Slope: no (relatively flat)
Site coverage ratio: 0.4
Number of floors: 2 full stories
Building type: detached construction, single-family or semi-detached houses allowed
Roof style: flat roof (max. 3° pitch, specified)
Maximum height: approx. 9 m (30 ft) to parapet
Special conditions:
• Green roof required
• Photovoltaic system planned / can be integrated effectively
• No underground garage allowed
Homeowners’ Requirements
The plan is not for a conventional single-family house but:
A single-family house to be used by two families, separated by floors
(confirmed provisionally by phone and building regulations, final feedback pending)
Concept:
• Ground floor: approx. 140–160 m² (1500–1700 sq ft) + garden
• Upper floor: approx. 150–160 m² (1600–1700 sq ft)
• Goal: long-term use, not an investment
• rather modern, clear architecture (flat roof is mandatory anyway)
Households:
• two families (each early 40s, each with one child)
Additional requirements:
• preferably quiet location within the development area (no through traffic)
• good orientation (garden ideally facing south)
• practical access / parking solution (2 garages + 2 carports planned)
House Design / Current Status
Who is designing it:
Currently do-it-yourself / concept phase
What is still open:
• Construction method (prefabricated vs. solid, wood vs. concrete)
• Floor plans
• Basement (partial vs. full)
Our Questions to You
Which plots would you generally prefer in such a development area (quietness, location, orientation)?
From your experience, are there any “typical mistakes” in plot selection that only become apparent later?
How critical do you consider the concept of “two families in one single-family house separated by floors” from a practical point of view (sound insulation, everyday life, usage)?
What would you pay special attention to regarding the placement of garage/carport and access?
We are aware that we are still early in the planning and open to honest feedback.
The concept is still under discussion, especially regarding a suitable second family. If anyone is in a similar situation or wants more information, just search for “Sonnenberg South-West”; we are happy to exchange ideas.
Thank you very much!
Best regards
Richard
We are currently at the beginning of a construction project in Ludwigsburg (Sonnenberg South-West development area) and would like to gather early feedback on the choice of plot and the overall concept.
The plots are allocated through an application process (up to 3 preferences possible, selection not guaranteed). We currently have 4 possible plots shortlisted and need to prioritize them.
Development Plan / Restrictions
Plot size: approx. 440 – 525 m² (4730 – 5650 sq ft)
Slope: no (relatively flat)
Site coverage ratio: 0.4
Number of floors: 2 full stories
Building type: detached construction, single-family or semi-detached houses allowed
Roof style: flat roof (max. 3° pitch, specified)
Maximum height: approx. 9 m (30 ft) to parapet
Special conditions:
• Green roof required
• Photovoltaic system planned / can be integrated effectively
• No underground garage allowed
Homeowners’ Requirements
The plan is not for a conventional single-family house but:
A single-family house to be used by two families, separated by floors
(confirmed provisionally by phone and building regulations, final feedback pending)
Concept:
• Ground floor: approx. 140–160 m² (1500–1700 sq ft) + garden
• Upper floor: approx. 150–160 m² (1600–1700 sq ft)
• Goal: long-term use, not an investment
• rather modern, clear architecture (flat roof is mandatory anyway)
Households:
• two families (each early 40s, each with one child)
Additional requirements:
• preferably quiet location within the development area (no through traffic)
• good orientation (garden ideally facing south)
• practical access / parking solution (2 garages + 2 carports planned)
House Design / Current Status
Who is designing it:
Currently do-it-yourself / concept phase
What is still open:
• Construction method (prefabricated vs. solid, wood vs. concrete)
• Floor plans
• Basement (partial vs. full)
Our Questions to You
Which plots would you generally prefer in such a development area (quietness, location, orientation)?
From your experience, are there any “typical mistakes” in plot selection that only become apparent later?
How critical do you consider the concept of “two families in one single-family house separated by floors” from a practical point of view (sound insulation, everyday life, usage)?
What would you pay special attention to regarding the placement of garage/carport and access?
We are aware that we are still early in the planning and open to honest feedback.
The concept is still under discussion, especially regarding a suitable second family. If anyone is in a similar situation or wants more information, just search for “Sonnenberg South-West”; we are happy to exchange ideas.
Thank you very much!
Best regards
Richard
Quick update: I have now received feedback from the city. This basically answers the two open points from my last post.
For me, this means the +50% allowance according to §19 BauNVO for ancillary structures applies. There is therefore a bit more leeway than I initially thought. This issue is no longer a dealbreaker but remains tight regarding parking spaces and building mass for 4 parking spaces.
Two equivalent residential units in the sense of a classic two-family house are therefore not envisaged.
Regarding partner search:
I have meanwhile discussed this with two specific families. We have jointly concluded that it does not make sense as it stands. The main reason is the city’s clear focus on single-family and semi-detached houses and the lack of support for a classic two-family house.
Even if it could be legally represented as a granny flat, the issues of ownership, division, and long-term stability remain too sensitive for us.
I will still submit a bid.
If I am awarded the contract, I would currently lean toward a classic single-family house (possibly with a granny flat) and rethink the concept.
I would then post here again and ask for your feedback.
This thread can be closed...
...a floor area ratio of 0.4 is set.
This means: Main structures include terrace areas and garages attached to the building (main floor area ratio 0.4). Ancillary structures are permitted up to 50% (+0.2 of the main floor area ratio), so the total floor area ratio can be up to 0.6.
For me, this means the +50% allowance according to §19 BauNVO for ancillary structures applies. There is therefore a bit more leeway than I initially thought. This issue is no longer a dealbreaker but remains tight regarding parking spaces and building mass for 4 parking spaces.
The building structure of the entire development area should also be maintained in the new construction phase, i.e. single-family houses and/or semi-detached houses are permitted.
In a single-family house, an additional granny flat (secondary unit) with a separate entrance is allowed.
If two independent families each occupy one unit, assessment is based on the legally required parking space ratio. Contrary to § 37 (1) of the state building code, at least 2 parking spaces per dwelling must be provided for detached single-family houses and semi-detached houses.
For each single-family house or semi-detached house with a granny flat, 3 parking spaces must be provided. “Trapped” parking spaces can be credited.
Two equivalent residential units in the sense of a classic two-family house are therefore not envisaged.
Regarding partner search:
I have meanwhile discussed this with two specific families. We have jointly concluded that it does not make sense as it stands. The main reason is the city’s clear focus on single-family and semi-detached houses and the lack of support for a classic two-family house.
Even if it could be legally represented as a granny flat, the issues of ownership, division, and long-term stability remain too sensitive for us.
I will still submit a bid.
If I am awarded the contract, I would currently lean toward a classic single-family house (possibly with a granny flat) and rethink the concept.
I would then post here again and ask for your feedback.
This thread can be closed...
N
nordanney29 Apr 2026 07:45mmyellow schrieb:
We have come to the conclusion together that it doesn’t make sense like this Nice to see you’ve now reached the conclusion we’ve been advising you about for six pages.
mmyellow schrieb:
If I get the contract, I would currently lean more towards a traditional single-family home (possibly with a granny flat) and rethink the concept. Fingers crossed that it works out for you.
mmyellow schrieb:
Two equivalent residential units in the sense of a traditional two-family house are therefore not planned in this way. From the quoted thoughts of the local development plan author, I do not read any discrimination against the classic duplex apartment building compared to the vertical two-family house. Only your concept of a stacked property, with a second party underpinning the main living unit with a flat-roof bungalow and placing a dimpled membrane like a Lego house on top, seems to me to cross the line between a wild idea and a hallucination and hardly has any chance of finding a like-minded supporter ;-)
That kind of nonsense isn’t really suitable for marine heating, just so you know, okay?
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
The land-use plan „Sonnenberg South-West, 2nd Development Phase“ specifies a floor area ratio of 0.4. This means: main structures include terrace areas and a garage attached to the building (main floor area ratio 0.4). Ancillary structures are allowed up to 50 % (+0.2 of the main floor area ratio), so the total floor area ratio can be up to 0.6. Matrose HeinBlöd checking in again on parking space surface scrubbing ?
Regardless of whether I get the plot or not:
This topic has completely captivated me by now and has already cost me several sleepless nights.
I’m currently trying to find the sweet spot between:
- 4 garages
or
- 2 garages + 2 carports
… and above all, the best arrangement for them.
That’s why I simplified plot 2 as follows:
- blue rectangle = building envelope approx. 13 × 21 m (43 × 69 ft)
- pink = 3 m (10 ft) setback on each side
- turquoise = 1 m (3 ft) setback from the street
- about 5 m (16 ft) to the street at the top
- about 7 m (23 ft) to the garden at the bottom
This leaves roughly a 13 × 15 m (43 × 49 ft) usable main building footprint.
Right now, I’m trying to understand the best logical layout for parking/garages.
My goal is to find the sweet spot that allows for the largest, yet sensibly usable rectangular footprint for the house.
Floor area ratio:
- Main structures 0.4 = 210 m² (2,260 sq ft)
- Ancillary structures additional 0.2 = 105 m² (1,130 sq ft)
- Total theoretically 0.6 = 315 m² (3,390 sq ft)
The big question now is:
What makes more sense?
- Counting “smaller” carports attached to the house?
- Or garages?
- Or keeping as much as possible freestanding?
Attaching everything completely to the main building seems rather difficult.
Then there’s the topic of the garden slab foundation.
I’m ignoring the walkways for simplicity for now.
I’ve already tried several variants, including some that probably violate regulations, just to better understand the limits.
Current boundary conditions:
- Boundary building max. 9 m (30 ft) on each side
- A total max. of 15 m (49 ft) along all boundaries combined
- Height max. 3 m (10 ft)
- Minimum 1 m (3 ft) setback from the street
Also, a garage doesn’t necessarily have to be 3 × 6 m (10 × 20 ft).
Maybe sizes like:
- 4 × 6 m (13 × 20 ft)
- 3 × 7.5 m (10 × 25 ft)
- 3 × 9 m (10 × 30 ft)
- or even 4 × 7.5 m (13 × 25 ft)
make more sense.
I also tried the option of a garage parallel to the street. However, nothing appealing came out of that because the space needed in front for maneuvering and parking takes up surprisingly much room.
And before we ignore the elephant in the room ?
Yes, I am aware that economically this is probably pure pipe dream and you could live more comfortably somewhere else for a lot less money.
But that’s not what this is about right now.
For me, this is currently:
- a thought experiment
- a feasibility analysis
- and honestly, it has even become a small hobby project ?
So no need to save me or point out that this probably doesn’t make financial sense. I know that.
I’m really interested in practical ideas.
Current questions:
4 garages?
Or 2 garages + 2 carports?
Garages side by side or staggered?
Directly attached to the house or deliberately freestanding?
Also, a garage doesn’t necessarily have to be 3 × 6 m (10 × 20 ft), but can also be 4 × 6 m (13 × 20 ft), or 3 × 7.5 m (10 × 25 ft), or both 4 × 7.5 m (13 × 25 ft).
And before someone pulls out the tall tales compass again ?
I’m neither an architect nor do I claim to be one. But these are exactly the kinds of topics I enjoy:
Understanding the constraints, researching myself, trying out different variants and attempting to optimize the puzzle reasonably.
I would really appreciate practical suggestions on how you would arrange a plot like this sensibly.
Feel free to just draw rectangles on my sketch:
blue = garage
orange = carport
gray = driveway ?
H
hanghaus202313 May 2026 12:43Somehow, the images are missing.
H
hanghaus202313 May 2026 12:53Is there a development plan? In Bavaria, you are allowed to build with the CP up to 3 m (10 feet) from the street, unless the development plan or a local regulation states otherwise.
A semi-detached house measuring 7.5 * 11 m (25 * 36 feet) should be livable. How tall is it allowed to be?
A semi-detached house measuring 7.5 * 11 m (25 * 36 feet) should be livable. How tall is it allowed to be?
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