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
G
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
G
GregorBerger3 Jun 2025 23:11Thank you for your design!
It’s a top-10 metropolitan area, although not right in the densely populated million-plus city. There, standard land value rates are well into four figures—sometimes even starting with a 2.
You generally only reach three-digit prices in this region if you are completely dependent on a car or move into areas with questionable schools and neighbors.
How far would that extension go? At 15 meters (50 feet) depth, you are already about 2 meters (6.5 feet) below ground level. And the rear area is actually supposed to have garages still.
By the way, the neighbor has excavated the slope all around their house. I’m not quite sure of the motivation yet. That must have cost a fortune—at least if they also had to dispose of the excavated soil. Their garden is somewhat higher overall though. Is it allowed to reuse excavated soil on your own property like that? If yes, that might be an idea for us as well. Then we could get closer to your suggestion.
I don’t think so anymore. And the reason is something I hadn’t considered despite years of reading. With a third full story, the house moves from building class 1 or 2 to building class 4. This has massive implications for fire protection, sound insulation, parking spaces, accessibility, and more. Surprisingly, I can’t recall any discussion where anyone really grappled with this topic. And a quick forum search didn’t reveal much either.
ypg schrieb:
Wow!
It’s a top-10 metropolitan area, although not right in the densely populated million-plus city. There, standard land value rates are well into four figures—sometimes even starting with a 2.
You generally only reach three-digit prices in this region if you are completely dependent on a car or move into areas with questionable schools and neighbors.
ypg schrieb:
I have another suggestion based on mine: the southern dwelling gets the basement on the ground floor level, extending some rooms there including a light well into the slope.
How far would that extension go? At 15 meters (50 feet) depth, you are already about 2 meters (6.5 feet) below ground level. And the rear area is actually supposed to have garages still.
By the way, the neighbor has excavated the slope all around their house. I’m not quite sure of the motivation yet. That must have cost a fortune—at least if they also had to dispose of the excavated soil. Their garden is somewhat higher overall though. Is it allowed to reuse excavated soil on your own property like that? If yes, that might be an idea for us as well. Then we could get closer to your suggestion.
ypg schrieb:
If you can actually afford that, the third full story is still an option.
I don’t think so anymore. And the reason is something I hadn’t considered despite years of reading. With a third full story, the house moves from building class 1 or 2 to building class 4. This has massive implications for fire protection, sound insulation, parking spaces, accessibility, and more. Surprisingly, I can’t recall any discussion where anyone really grappled with this topic. And a quick forum search didn’t reveal much either.
G
GregorBerger3 Jun 2025 23:18GregorBerger schrieb:
With the third full story, the building classification changes from Class 1 or 2 to Class 4.Sorry, that was a bit simplified. The third full story would have its floor level only about 5 meters (16 feet) above the average natural ground level (assuming the slab is at street level). However, the third full story would only really increase the living area if there was also a finished attic above it. That attic would have its floor level just over 7 meters (23 feet) above ground – which would then make it a Class 4 building.
GregorBerger schrieb:
My current home office is 7m² (75 sq ft). And that’s invaluable compared to the workspace in the living room of my previous apartment a few years ago. Definitely more useful than having an extra 7 square meters in the living room. And yes: it fits everything I need for my work. Seven square meters as space for a desk and a chair – where you can hang your jacket – is more than enough, almost luxurious for a small room dedicated to doing your tax return. But that’s only about twenty cubic meters, which for a full-time workstation with a mechanical ventilation system with heat recovery can mean an increased idle air flow rate. So either permanently tilted windows or a non-smoking balcony.
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
G
GregorBerger19 Jun 2025 10:26Good morning forum members,
there are a few updates.
I had an initial consultation with an architect. Although she will most likely not be able to plan the new build, as she is not accepting any new planning commissions this year, I still sought the conversation because she is the leading expert in the area of single-family, two-family, and three-family houses here in town.
Some surprises emerged that show even extensive internet research and years of reading house building forums have their limits. I was particularly surprised by the following points (to my disadvantage):
Some of this is quite disheartening. Have any of you had your own experiences with these issues?
Best regards, Gregor
there are a few updates.
I had an initial consultation with an architect. Although she will most likely not be able to plan the new build, as she is not accepting any new planning commissions this year, I still sought the conversation because she is the leading expert in the area of single-family, two-family, and three-family houses here in town.
Some surprises emerged that show even extensive internet research and years of reading house building forums have their limits. I was particularly surprised by the following points (to my disadvantage):
- The municipality opposes the parking space regulations of NRW (there is no separate local ordinance) at points that are precisely worded and actually leave no room for interpretation, which will increase the parking space requirement on my property by one parking space in most scenarios.
- The (favourable for me) height data in TIM NRW have no legal relevance in terms of building regulations. In fact, no relevant height data is available to anyone, not even the municipal administration. Only the involvement of a publicly appointed surveyor results in an official site plan that also shows the terrain profile. I have already spoken to the surveyor: the rather steep incline from the street shown in TIM cannot be found on the property, as this property and those of both neighbours have been levelled down to street level across approximately 20 meters (65 feet) in depth and along the full width. When natural terrain is no longer recognizable, the surveyed existing terrain becomes decisive.
- The building authority generally does not offer oral consultations. You can only submit a preliminary building inquiry, which takes about 3 months to process. Since the zoning plan contains some vague wording, this carries a certain risk.
- Fire protection for GK1 and 2 (single-family and two-family houses) must include an escape plan without the use of an aerial ladder. This means that the second escape route fundamentally requires access from every floor to a window, balcony, or flat roof where the fire department can set up a portable ladder. This would not be possible with the current concept of two semi-detached houses arranged one behind the other. Does anyone know where I can find more information on this?
- A building permit here takes about 10-12 months to be approved. Of that, 3-4 months alone are spent on the water law approval, which is handled at the district level.
Some of this is quite disheartening. Have any of you had your own experiences with these issues?
Best regards, Gregor
GregorBerger schrieb:
If the natural terrain is no longer identifiable, then the existing terrain would simply be surveyed and taken as decisive.But that is not "to your disadvantage."GregorBerger schrieb:
Since the development plan contains some vague wording, there is a certain risk involved.And within that, there are rather opportunities to use uncertainties in favor of the applicant.GregorBerger schrieb:
That would not be possible with the current idea of terraced semi-detached houses.One more argument in favor of my proposal for the classic two-family house with apartments on separate floors.https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
GregorBerger schrieb:
I had an initial consultation with an architect. Although she probably won’t be able to plan the new build, as she is not taking on any new planning projects this year, I still reached out because she is the leading expert here in the area for single-family homes, two-family homes, and triplexes. That’s normal (it’s the same for me), that the schedule is already full by June. Are you at least able to get appointments with her for Module A still this year?
https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/
Similar topics