ᐅ Semi-detached house within a building plot measuring 8.5 m by 15 m (width x depth)

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:

• 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