What the neighbours may still build — and how much sun you would keep
A flat is bought for the sun it has today. Whether it still has it in ten years is decided by the building class of the houses around it: whoever stands lower than allowed may add storeys. Azima raises every neighbouring building to the upper limit of its building class and calculates the three reference days again — today against built out.
The city’s roof model records what is built, the zoning plan what may be built. In many Viennese lanes a whole storey lies between the two: a Biedermeier house with twelve metres of eaves in building class III may grow to sixteen, while the Gründerzeit block next to it already stands above that. For the flat opposite, that is the difference between winter sun and none.
Try it on one address →What is computed — and where it stops
The calculation is deliberately the upper bound: every neighbouring building rises vertically to the permitted height, with no roof, no setback and no question of whether anyone will ever build. That does not make it a forecast but a statement of how much light would remain in the worst permitted case. A figure near zero is not a verdict on the flat — it is a question worth asking before buying.
Frequently asked
Does that mean the neighbours will add storeys?
No. It only means they would be allowed to under the building class. Whether, when and how anything is built, no register says; a protection zone or a stricter height in the development plan can rule it out entirely.
Why today and built out side by side?
Because the difference is the question: a pair like "2.4 hours today, 0.5 built out" says more than either figure alone — and "today" is the same figure the light widget shows for this floor.
Does it apply to every floor?
The calculation runs at two heights: from the ground floor to the second floor, and from the third floor up — the same two steps as the other figures on the page. Higher up less is usually lost, because even built-out neighbours rarely reach above eye level.
What about trees?
Trees are drawn in the view but do not cast shade in the calculation — not in the built-out case either. A tree grows, gets pruned and loses its leaves in winter; a building does none of that.
Is it in the report?
Yes, as a sentence on the sheet "For the conversation": how many neighbouring buildings may still grow and how much sun would be lost on the hardest reference day. A measured drawback is not left out; it is explained.
All measurements · For agents & developers · The light check
Basis: the City of Vienna LoD2.1 roof model and zoning plan (data.wien.gv.at, CC BY 4.0), building classes under § 75 of the Vienna Building Code, solar positions computed astronomically. The upper bound of a risk — not a forecast, not legal advice.