ᐅ Build a Duplex or Two Single-Family Homes on One Lot?

11ant schrieb:
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You could both do without the distance between your individual houses and build them as close together as semi-detached houses are usually placed.... ?

I am quite certain that, among other reasons, fire safety regulations do not allow waiving the regulated setback distance. Explaining or justifying this here would go beyond the scope. Any building authority could provide an official statement on this.

Personally, I do not see any advantage in squeezing two single-family homes into that space. The building envelope offers no flexibility to expand or design the house more freely. With a 6 x 10 meter (20 x 33 feet) footprint, there is hardly any room... well, the space is negligible 😉

Furthermore, single-family home lots must meet a minimum size requirement. This depends on the municipality, the development plan (planning permission/building permit), and infrastructure. It is not uncommon in purely residential areas to require 500 or 650 square meters (5,380 or 7,000 square feet). In very rural areas, lot sizes are even larger with lower floor area ratios...

Rob1107 schrieb:
It’s still worth checking whether there might be space for two detached houses.

The evaluation is straightforward:
a) 18 m (59 feet) width divided by two, without any gap between, results in 2 x 9 m (30 feet) width.
b) 18 m (59 feet) width minus a 6 m (20 feet) gap in between gives 2 x 6 m (20 feet) width, allowing each house one additional exterior wall and one extra windowed side.
c) 18 m (59 feet) width minus a 3 m (10 feet) gap in between gives 2 x 7.5 m (25 feet) width, and each house has an extra exterior wall for heat dissipation, although this wall is less effective as a windowed side.
Conclusion: semi-detached house.

Rob1107 schrieb:
whether the building setback distance could be reduced.

Only between your two houses (for a semi-detached house down to zero). I don’t see any possibility to reduce distances to neighboring properties. So it’s always 18 m (59 feet) from the left corner of the left house to the right corner of the right house.

Rob1107 schrieb:
Two detached houses are, in our opinion, more attractive than one semi-detached house.

With that opinion, you are mistaken for this plot (or only one house fits). However, I find a 9 m (30 feet) house width per side practical.

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Nordlys schrieb:
Clear statement. This is a detached house plot. Or just a single-family house. Anything else is nonsense.

... says the East Holstein native who uses walking sticks for a stroll around the plot
two detached houses!
... says the Northern German terraced house owner in Westphalia, familiar with many building plots under 200m² (2150 ft²).
The plot is estimated to be 800m² (8600 ft²), so if divided, 400m² (4300 ft²) remains for each party. The minimum setback distance in Baden-Württemberg is 2.50m (8 ft 2 in). If the street-side building boundary is not a building line, there is no obligation to build parallel to the street. For the northern plot (top of the plan facing north?), a rectangular building footprint is obviously not possible due to the building boundaries. However, an architect can design two decent detached houses here, provided there are no further unknown zoning plan restrictions (see @ypg). In that case, no reduction of the minimum setback would be necessary. Such a reduction is possible under certain conditions (e.g., party walls without openings, see §6 LBO_BW), but not advisable (see @11ant).

Oh God... South German laying hen farming..., Karsten

Nordlys schrieb:
Oh God... southern German egg-laying hen farming...., Karsten

3 comments, all unhelpful... thumbs up, Karsten....
The plot is located right by Lake Constance. Land prices here are simply astronomical. You can get 110sqm (1,184 sq ft) of living space in a detached house built in 1970 for just €750,000. Swiss buyers are bidding thousands more… so much for the “egg-laying hen farming” topic... there simply are no plots available for ordinary people.
Whether you want to interpret this as “egg-laying hen farming” is up to you. It seems you are fortunately in a better position with more options. Unfortunately, that is not the case here, so we want to leave no stone unturned to find the best solution for both parties with the means (plots) available to us.
The question was simply whether it would be possible to fit two detached houses on the plot while complying with building regulations (building permit/planning permission). Personal opinions are welcome, but preferably in a constructive way. We are still not very experienced in this field, so we rely on advice and opinions from friends, family, and forums.

Nordlys schrieb:
Oh God... southern German laying hen farming..., Karsten

I grew up exactly where you live. My parents built several times in new developments, and the typical plots there were always under 400cm (157 inches).

Your other descriptions of the local conditions also remind me more of stories from my grandparents than of the reality I have experienced – just charming folklore, really.