A real two-family house with similarly large living space

Hello everyone,

firstly our objective and the facts, at the end then our questions. we look forward to your comments :-)

Thank you very much

Objective:
Two-family house for families with maximum utility (reasonable); best possible use of living space on the property or utilization of the development plan; equality of the two residential parties regarding light (south orientation for living rooms, light wells for the basement) and comfort; energetically fulfilling KfW40


Development plan/restrictions
Size of the property: 810 m² (18x45 m, rectangular, narrow side to the traffic area and to the south or north; no trees, bushes, etc.)
Neighboring buildings: detached houses
Slope: none, nicely flat
Floor area ratio: 0.2, extension „may be exceeded up to a floor area ratio of 0.5“
Floor space index: 0.4
Building envelope: 12x40 m; building line and boundary: at least 5.0 m distance between public traffic area and main building or garages and 3.0 m to each neighboring property; max. 120 m² footprint
Edge construction: no information
Number of parking spaces: no information
Number of floors: 2 full floors
Roof shape: none specified, in the street there are hipped roofs, gable roofs, clipped gable roofs, and mansard roofs
Architectural style: none, the houses in the street have various styles, from Italian-style houses to brick bungalows
Orientation: not specified
Maximum heights/limits: plinth height max. 0.80 m; eaves height max. 4.30 m; ridge height max. 8.80 m to the nearest manhole cover (which is approximately standard curb depth, about 20 cm?)
Other specifications: tree planting on the property, initially not relevant for the building


Builders’ requirements
Architectural style, roof shape, building type: none, preferably mansard roof for better use of the attic
Basement, floors: fully developed and usable basement + 2 full floors + attic
Number of people, age: 2 families with 1-3 children
Space requirements on ground floor and upper floor: each apartment 120-140 m²
Overnight guests per year: 1 guest room each would certainly be nice
Open or closed architecture: open design (3 m boundary to neighbor’s property must be maintained on both sides), if that is what is meant
Conservative or modern construction: goal is KfW40, solid construction no prefab house
Open kitchen, kitchen island: currently undecided
Number of dining seats: 6-8 persons
Fireplace: no, not planned
Balcony, roof terrace: terrace for one apartment and balcony for the other apartment
Garage, carport: double garage + 2 open parking spaces (possibly carport?) with e-charging options
Other: no concrete ideas, initially what would be possible within the framework conditions


House design
Who made the plan: self-made with Roomsketcher
What do you like especially? Why?: from the kitchen to the living room there should be large sliding doors to create a kind of eat-in kitchen but not necessarily (to avoid cooking smells); the bathroom should each be about 10 m² to be comfortably large; the lower apartment should be barrier-free
What do you not like? Why?: the staircase on the 1st upper floor to the attic theoretically intrudes into the guest room, somehow suboptimal
Price estimate according to architect/planner: I estimate around 520,000 €
Preferred heating technology: ground source heat pump


If you have to dispense with something, which details/extensions
-you can do without: mansard roof, if otherwise you can also achieve the 2 x approx. 120 m²
-you cannot do without: 2 apartments, each with at least 4 rooms


Why did the design turn out as it is now?
Target specification: We looked at floor plans of prefabricated houses and oriented ourselves by them and our current apartment


What is the most important/basic question about the floor plan summarized in 130 characters?
Is the assumption of the floor area ratio / requirements of the development plan correct?


Our questions:

[*]Floor area ratio: property size 810 m² with floor area ratio 0.2 (=162 m²); restriction: footprint for detached house maximum 120 m²
What can I count in the difference of 42 m² (balcony, bay window, light shafts, light wells, terrace…)?
[*]Extended floor area ratio: for garages, etc. „the floor area ratio may be exceeded up to 0.5“. What is meant mathematically by this? Half the property area (405 m²), half the property area minus the floor area ratio (405-162 = 243 m²), half the floor area ratio (81 m²) or half the footprint of the detached house (60 m²)?
[*]What do light wells (planted slopes, no basement shafts attached to the house) for basement daylight count towards, floor area ratio or extended floor area ratio?
[*]What do balconies or overhanging bay windows count towards?
[*]Which wall thicknesses for exterior walls (KfW 40 with brick cladding) and interior walls should we expect?

Pictures attached:

I have forgotten the other framework conditions: Wall thicknesses currently planned with 465 mm on the outside and 240 mm on the inside. Room heights 2.5 m on the ground floor and 1st floor and slightly lower in the attic.

And forget to include the street and north arrow in the site plan ....

Presumably, everything fails because of the staircase .. Outside 404 cm - wall thickness 93 cm = 311 cm for the staircase, which remains the main traffic route (also for moving furniture, kitchen countertops, etc.) for a two-family house.

Why no DH? I do not want to move into either of the two apartments. [Lichthof] is not daylight, [Terrasse] no garden access. Why should the [EG] be wheelchair accessible?

Is there a development plan?

Mark the property on the aerial image.

A plan of the property? Preferably from the Geoportal. At least you can see where north is.

In case it is a 34er, photos of the neighboring development are important.

I see 4 floors of 90 sqm each? I would initially advise to get information about construction costs. 520k is completely unrealistic.