ᐅ Semi-detached house within a building plot measuring 8.5 m by 15 m (width x depth)
Created on: 20 May 2025 19:02
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GregorBerger
Dear housebuilding forum,
After several years of searching, we have finally purchased a plot of land (with an existing building to be demolished) in our desired location. This also marks the end of my many years of purely passive participation in this forum. Since we were primarily looking for renovation projects rather than new builds, we naturally have some initial questions.
The plot, approximately 500 m² (5,400 sq ft), lies within the scope of a development plan that was last updated 20 years ago.
Basic data about the plot and development plan:
The development plan places no restrictions on, among other things:
The plan is to build a semi-detached house with another family. Both families have two children each and require two home offices, resulting in a need for six rooms per semi-detached unit. If we make progress here, I will create another thread in the floor plan forum and fill out the questionnaire.
Since the building envelope width of 8.5 meters (28 ft) is too narrow for semi-detached units side by side, they would have to be arranged one behind the other. Garden access and terraces would then be located on the narrow sides (one facing the street and one facing the main garden at the rear). This type of semi-detached house is quite rare. I have looked around in real life but have not found any examples. Only the Büdenbender semi-detached house Gemello SD 135 roughly corresponds to this layout (though not to the measurements).
I have had some informal discussions with an architect I know (who now only works on office buildings) and the building authority, without encountering any fundamental contradictions so far.
I have already applied the @11ant basement rule, according to which a basement seems obligatory because there is more than 2 meters (7 ft) of height difference within the building envelope. However, I do not understand how this relates to the “base (plinth)” restriction of max. 60 cm (24 in) in the development plan. My layperson assumption would be that one floor (the ground floor? the lowest residential floor? the lowest full floor?) may start a maximum of 60 cm (24 in) above street level.
My first questions for you:
Thank you in advance,
Gregor
After several years of searching, we have finally purchased a plot of land (with an existing building to be demolished) in our desired location. This also marks the end of my many years of purely passive participation in this forum. Since we were primarily looking for renovation projects rather than new builds, we naturally have some initial questions.
The plot, approximately 500 m² (5,400 sq ft), lies within the scope of a development plan that was last updated 20 years ago.
Basic data about the plot and development plan:
- Building is permitted from 3 meters (10 ft) to 18 meters (59 ft) depth (so 15 m (49 ft) for the house)
- After deducting setback areas, a width of 8.5 meters (28 ft) is possible
- Slight slope across the building envelope with a rise of approximately 2.2 meters (7 ft)
- 3 full floors permitted
- Site occupancy index (ground coverage ratio) 0.4
- Floor area ratio 1.2 (cannot be fully utilized due to the aforementioned building envelope)
- Roof pitch 35–45°
- Knee wall (dormer wall) height 60 cm (24 in)
- Base (plinth) max. 60 cm (24 in) above the midpoint along the width of the access area, which is itself 30 cm (12 in) lower than the start of the building envelope
- General residential zone
- Open building style (detached buildings, no shared walls)
- Covered terraces allowed up to 1.5 meters (5 ft) outside the building boundary, provided the site occupancy index is not exceeded
- Roof indentations and structures permitted up to half the eaves length and at least 1 meter (3 ft) from the gable wall
- Fencing with native hedges. Along the street, an additional fence up to 1.2 meters (4 ft) high is permitted.
The development plan places no restrictions on, among other things:
- Building type
- Number of residential units per building
- Height limits
- Basements
- Parking spaces
The plan is to build a semi-detached house with another family. Both families have two children each and require two home offices, resulting in a need for six rooms per semi-detached unit. If we make progress here, I will create another thread in the floor plan forum and fill out the questionnaire.
Since the building envelope width of 8.5 meters (28 ft) is too narrow for semi-detached units side by side, they would have to be arranged one behind the other. Garden access and terraces would then be located on the narrow sides (one facing the street and one facing the main garden at the rear). This type of semi-detached house is quite rare. I have looked around in real life but have not found any examples. Only the Büdenbender semi-detached house Gemello SD 135 roughly corresponds to this layout (though not to the measurements).
I have had some informal discussions with an architect I know (who now only works on office buildings) and the building authority, without encountering any fundamental contradictions so far.
I have already applied the @11ant basement rule, according to which a basement seems obligatory because there is more than 2 meters (7 ft) of height difference within the building envelope. However, I do not understand how this relates to the “base (plinth)” restriction of max. 60 cm (24 in) in the development plan. My layperson assumption would be that one floor (the ground floor? the lowest residential floor? the lowest full floor?) may start a maximum of 60 cm (24 in) above street level.
My first questions for you:
- Are you familiar with similar houses, possibly with names for Googling or similar?
- Would you approach this topic differently?
- What does the rule about the base (plinth) mean?
Thank you in advance,
Gregor
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hanghaus202322 May 2025 11:45A simple thank you is sufficient. The best way to show appreciation is by answering questions and providing more information. So, thank you from me as well.
11ant schrieb:
For me, thanks can be sent via PayPal. That works well too. Amazon gift cards are also a good option.
GregorBerger schrieb:
Well, there are quite a few houses with less than 50 sqm (540 sq ft) of living space on the ground floor and 6 rooms. The difference is, they’re not square-shaped—and they usually have more than just 2 stories like the typical “city villa.” I didn’t say otherwise. But you do have this kind of clear limitation.
GregorBerger schrieb:
Half a million. Wow!
GregorBerger schrieb:
None of those are what we want. That would probably have been created by the floor plan form. But we’re not there yet... You’d be the first, after a lot of thinking, who wouldn’t say, “actually, I want it differently.” Usually, the wife gets blamed then.
GregorBerger schrieb:
Looks very interesting, but I don’t fully understand yet. Two-story with a basement on a slope + first floor (garden level) + second floor. Flat roof is not possible, so another attic on top? Where exactly is the dividing line between the two residential units? The dividing line is simply in the middle. Garden level: first unit on the ground floor south, garden level: second unit in the “first floor” north, which is basically the upper ground floor for the second unit. You can see that from the side entrance door.
The third story (which is the second for the second unit) I only created roughly without windows, and no roof yet. It all takes time.
Here, it’s definitely about the shares for both residential units.
kbt09 schrieb:
Two stories, so about 90–96 sqm (970–1030 sq ft) plus attic would be the result of @hanghaus2023’s study in post 33, and then there still needs to be... I have another suggestion based on mine: the southern unit would get the basement at ground floor level and extend rooms there, including a light well on the slope. The northern residential unit would get the attic, so the visible third story under the roof. That way, each would have 1½ stories of the two-family house. If you can afford that, then a third full story would also be an option.
GregorBerger schrieb:
The idea is also to have a separate floor for the home office, as far away as possible from the noise on the ground floor. In maisonettes, for example, the ground/basement level and the upper/attic level.
GregorBerger schrieb:
All of this would probably be outlined in the floor plan form. But we’re not there yet... Which floor plan form?
GregorBerger schrieb:
It’s not set in stone that the two semi-detached units have to be completely identical. They wouldn’t be able to in this case either. However, you haven’t yet provided any indication of what differences the room layouts would have.
I still don’t really understand how the concept works: You bought the plot of land, and the family friends are only stakeholders in a vague joint building project and will just receive a surprise half? – Yvonne already hinted that the gap between expectations and reality could turn into a breaking point. Do you really have the authority to accept extremes like “unfortunately, there was no room left for you” or “you get the uglier half, but it’s cheaper” for the friends?
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
GregorBerger schrieb:
The plot allows for a 127 m² (1,367 sq ft) footprint and 3 full floors (+ attic + possibly a basement on the slope). That results in something between 400 and 500 m² (4,305 to 5,382 sq ft) of floor area – which is more than enough for 2 families with a total of 4 home offices. A 127 m² (1,367 sq ft) footprint permitted for building (15 by 8.5 m (49 by 28 ft)) does not translate into 400 to 500 m² (4,305 to 5,382 sq ft) of living space, but rather a maximum of 48 m² (517 sq ft) of living space per floor per dwelling unit.
@hanghaus2023 ... how would you arrange the two garages and one parking space each given these side entrances shown in post 35? I don’t see how that can work. There seems to be no space at all within the 6 m (20 ft) from the street to the start of the building zone to accommodate them.
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GregorBerger3 Jun 2025 13:43Hello everyone,
I have received a lot of input here that I first needed to process. Meanwhile, the plans have further developed, and new questions have also come up. Now I will first respond to your points.
How is the plinth height defined for a sloped site? In other contexts, the height is usually the average height of the slope. But that makes little sense for the plinth, since at the upper end of the slope the plinth would disappear into the ground.
Very interesting idea! What is allowed for gable roofs with a pitch of 35-45°?
Different roof pitches on each side?
Offset shed roof?
Same pitch but ridge not centered?
Wait, I was referring to the total floor area of the entire building, and you are talking about living area per floor per dwelling unit. That’s an apples-to-oranges comparison—and not even contradictory to my statement. What point were you trying to make?
I have received a lot of input here that I first needed to process. Meanwhile, the plans have further developed, and new questions have also come up. Now I will first respond to your points.
hanghaus2023 schrieb:
I even sketched that first. But I’m not sure whether the plinth height speaks against it. In any case, it’s an approach.
How is the plinth height defined for a sloped site? In other contexts, the height is usually the average height of the slope. But that makes little sense for the plinth, since at the upper end of the slope the plinth would disappear into the ground.
11ant schrieb:
In the boldest case, perhaps even an asymmetric gable roof with the ridge over the rear half (and in a way a shed roof over the front), to be able to set the rear one story higher…
Very interesting idea! What is allowed for gable roofs with a pitch of 35-45°?
Different roof pitches on each side?
Offset shed roof?
Same pitch but ridge not centered?
GregorBerger schrieb:
That results in something between 400 and 500 m² (4,300 to 5,400 sq ft) of floor area—more than enough for two families with a total of four home offices.
kbt09 schrieb:
127 m² (1,367 sq ft) footprint allowed for construction (15 x 8.5) does not lead to 400 to 500 m² (4,300 to 5,400 sq ft) of living space, but rather a maximum of 48 m² (520 sq ft) living space per unit per floor.
Wait, I was referring to the total floor area of the entire building, and you are talking about living area per floor per dwelling unit. That’s an apples-to-oranges comparison—and not even contradictory to my statement. What point were you trying to make?
GregorBerger schrieb:
Wait, I was referring to the total floor area of the entire house, and you were talking about the living area per floor per housing unit. That’s comparing apples and oranges—and not even contradicting my statement. What point were you trying to make?127 sqm (1370 sq ft) building plot for 2 halves of a semi-detached house. Based on the design by @hanghaus2023, that means per semi-detached house, i.e., per housing unit: exterior dimensions of 7.5 × 8.5 m (25 × 28 ft).
After subtracting exterior and interior walls, each floor has about 48 sqm (517 sq ft) of living space. Three floors amount to approximately 144 sqm (1550 sq ft) per semi-detached house, so around 288 sqm (3100 sq ft) total for the two, thus under 300 sqm (3229 sq ft) of living area.
This was in response to
GregorBerger schrieb:
That results in something between 400 and 500 sqm (4305 and 5382 sq ft) of floor area—which is more than enough for 2 families with a total of 4 home offices.which implies a much larger living area that should be put into perspective by comparing it with typical house floor plans. Also, see post 34 for further reference.
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