Floor area ratio calculation when 2 parcels need to be combined

In the present case with the OP, I also fear that the area of the access plot may not be taken into account for the floor area ratio potential. But it would probably be silly anyway, because if it is not paved to allow infiltration, here a fully sealed area would probably even deduct something...

Such an independent access parcel of land of course cannot borrow any floor area ratio from the served properties and must also observe the corresponding quota itself. So one must be content with paving only the driving lanes there ...

Thank you very much for your previous assessments. How the floor area ratio can be adhered to on the respective plots is currently being considered. It is clear that it will be tight. To better assess this, it would be helpful to know how this works with 2 parcels. My concern is less that one cannot use the driveway parcel when dealing with the house parcel, but more the concern of how the floor area ratio can even be maintained on the driveway parcel. Because if a parcel is basically used 100% for access (in combination with the path to the front doors) and then has to comply with a floor area ratio, how can that work? And if the driveway then, for example, also has to draw on the floor area ratio of the house, it will really be tight. The location is by the way Hamburg and §34 Baugesetzbuch applies. Whether it can be argued here with driving lanes or permeable material, I still have to find out.

Who is the seller? Is there a preliminary building inquiry?

If I remember correctly, there is no official floor area ratio in §34 areas anyway. You only have to orient yourself by the measure of the usual development. So look out for pure access plots in the online cadastre. And in reality, see how it has been implemented there.

There is no written building inquiry. The buildability was clarified by our general contractor (by phone) with the building authority, which has signaled its approval for the current plans.

In the immediate vicinity, I cannot identify a purely access property. There is a plot of land which serves as the footpath to the houses partly located far back on the property, and something that looks like an access road to houses further back, but is considered part of the street. The property 2 houses further looks like it is 80% concreted according to Google. But I lack the knowledge to assess its impact on the surrounding development.