ᐅ Unclear exact building size within the building envelope

Hello everyone, a perhaps simple question, since I haven’t found any previous discussion on this topic:

We are currently in the process of buying a plot of land in an established residential area. We plan to build an extension attached to an existing semi-detached house. There is a development plan from 1991 that is still valid. However, I cannot find any dimensions in the plan indicating how large the house can be. It specifies a floor area ratio of 210 sqm (2,260 sq ft) and a site coverage ratio of 105 sqm (1,130 sq ft), but nothing else.

As a layperson, it’s unclear to me how to derive any specific measurements (like 9x10, 9x9, or 11x9 meters) from this information. One option might be to submit a preliminary building inquiry, but we would prefer not to do that at the moment. Are there any other ways to determine the size of the building envelope?

Good luck

DaioDollaz schrieb:

There is a floor area ratio of 210sqm (2,260 sq ft) and a plot ratio of 105sqm (1,130 sq ft) and nothing else.

That’s all you really need. The development plan itself may specify in writing how much distance must be kept from the street or how an extension to an existing semi-detached house should be built (aligned or set back). Building on the boundary line is regulated by the applicable state building code anyway. So if no exceptions apply, the general rules are valid. Nothing more is necessary and, in fact, it is a straightforward arrangement.

DaioDollaz schrieb:

As a layperson, it’s not clear to me how to arrive at any specific dimensions (9x10; 9x9; 11x9).

You basically have a choice.

However, I find it surprising that you didn’t include a plan with your question right away.

DaioDollaz schrieb:

We are currently in the process of buying a plot of land in an established residential area. We are attaching our build to an existing semi-detached house, and there is a development plan from 1991 that is still valid. However, I cannot find any dimensions in the plan that specify how large the house can be. There is a floor area ratio of 210m² (2260 sq ft) and a site coverage ratio of 105m² (1130 sq ft), and nothing else.

Please provide the name of the development plan (without a link). How old is the neighboring half, and why is it a standalone structure?
Take a look at my posts under the keywords "with basement owner" / "without basement owner" or underpinning. An important aspect is the matching profile along the shared party wall / "common wall." There is no shortage of semi-detached house threads here.

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Hello everyone, thank you! Attached is the site development plan with some adjustments—I only removed the name of the location and the scale (1:500).
The other half was built in 1998, and since the owner of the plot has passed away, we can also build there as we will be purchasing it soon (in 2 weeks).
The neighbor has a basement, but we are currently undecided whether it is financially feasible. It is definitely not necessary. Therefore, the points mentioned above from the threads are met (the house with a basement was built before the one without a basement), but of course, we would still have to extend the building, with all the related pros and cons. Roof pitch, ridge height, etc., are all predetermined; only the length of the house might still be an interesting issue, but so far I don’t see any problem with that since we haven’t started the planning yet. As mentioned, it is still unclear how large the building footprint is allowed or possible to be, but maybe you can get more information from the development plan.
The plot is parcel 2019 “westside.”

You can see the boundary line around the "house." Definition:

DaioDollaz schrieb:

This is parcel 2019 "westside" :-)

This allows you to build a semi-detached house identical to the neighbor’s. Not larger, but smaller would be possible.

However, I believe you mean parcel 2016. At least according to the aerial image/maps, otherwise I wouldn’t know where you intend to extend.

You can also check your plot on the Geoportal site (2012/19?). Without more information, though, it would also just be a duplicate of house number 1/4.

DaioDollaz schrieb:

There is a floor area ratio of 210 sqm (2260 sq ft) and a site coverage ratio of 105 sqm (1130 sq ft) and nothing else.

Where does it say that?
It only states a site coverage ratio of 0.4 and a floor area ratio of 0.8.
The plot size is therefore 262.5 sqm (2825 sq ft) by calculation. There is a specific building envelope. The house must fit within this. The blue line and the dotted, dashed line.
However, the 2019 West plot dimensions only allow less than 200 sqm (2150 sq ft) – 20 x 10 meters (66 x 33 feet) and a bit of the plot taken up by a roundabout.
Check again which plot it could be.