Floor Area Ratio - Significance for Construction Projects

Good day,

I intend to purchase a plot of land in an existing development area (in Hessen). In the development plan, which dates from 2005, the eaves height is specified as 4m from the ground edge of the ground floor, and the ridge height as 5m from the upper edge of the top full floor. The number of floors is limited to 1.

We can probably forget about the originally planned town villa anyway due to the eaves height, but does maximum number of floors 1 mean that I am also not allowed to build a basement or an attic with corresponding slopes?

Best regards

In the development plan, which dates from 2005, the eaves height is specified as 4m from the ground edge of the ground floor, and the ridge height as 5m from the top edge of the uppermost full storey.
The number of storeys is limited to 1.

The latter is a very unusual definition, but at least understandable for laypersons, at least by the standards of development plan texts. Apparently, as usual, only the number of full storeys is limited.

but does maximum number of storeys 1 mean that I am also not allowed to convert a basement or attic with corresponding slopes?

No. Apparently, they want to allow an attic with about one meter knee wall and overall quite decent usability. For the basement, of course, you have to be careful not to turn it into a full storey.

The originally intended city villa can probably be forgotten anyway due to the eaves height,

Yep!

that I am also not allowed to finish a basement or attic with corresponding slopes?

... a look into the state building code is a must before planning to build a house?! It's stated there what concerns the attic and basement.