ᐅ How is the maximum allowable living area calculated?

Hello everyone,

I am currently planning a semi-detached house on a sloped site and have run into a major problem that is causing me a lot of frustration. Maybe someone here can help me understand it better.

Here are the key details:

• Plot size: 217 m² (2337 sq ft), floor area ratio: 0.45 → maximum buildable footprint of 97.65 m² (1051 sq ft).
• No floor space index specified.
• 1 full storey allowed, with a gable roof at 35° pitch (eaves height max. 4.50 m (14.8 ft), ridge height max. 9.00 m (29.5 ft)).
• Currently planned living area: 131 m² (1410 sq ft) (ground floor and attic).
• Balcony: 7.5 m² (81 sq ft); I wanted to make it a bit larger.

My architect strictly refuses to enlarge the balcony, saying that this would exceed the maximum allowable living area. However, he does not explain in detail how this limit on the maximum living area is calculated. There seems to be an absolute limit that, according to him, must not be exceeded. I understand that the ground floor footprint is clearly restricted by the floor area ratio (97.65 m² (1051 sq ft)). But how is the maximum possible living area in the attic calculated? The eaves height, ridge height, and roof pitch naturally limit the usable space—but what is the basis for determining this maximum area? I haven’t received any convincing explanations from my architect on this.

I am currently quite at a loss and would appreciate any help to better understand this or any advice on how to proceed. Thank you very much in advance!