# Will the new block take the sun from your window?

Type the flat's address, pick the floor and the facade, then put an imaginary block in front of the window. See how many hours of direct sun you get on every day of the year, above all on 21 December.

A 30 m block casts a shadow 74 m long at noon on 21 December and 11.5 m long on 21 June. In winter a block across the street can cover the Sun; in summer, at solar noon, the shadow is much shorter — though nearby buildings can still shade the window, especially in the morning and evening.

Romanian law requires residential buildings to be placed so that living rooms in the building and in neighbouring homes get at least 1 hour 30 minutes of sun at the winter solstice. Here you see how much your window gets.

## How many hours of sun does the law require in a flat?

Ministry of Health Order 119/2014 says, in article 3 of the annexed Norms, that residential buildings must be placed so that living rooms in the building and in neighbouring homes get at least 1 hour 30 minutes of sun at the winter solstice, around 21 December.

If the distance between neighbouring buildings is smaller than or equal to the height of the tallest one, the project must include a sunlight study showing the threshold is met.

In the table in the tool, the winter solstice row carries a mark: “≥ 1 h 30” or “< 1 h 30”. Our calculation covers a single point on a facade. It is not an architect's study, so it does not decide whether a building complies. It does tell you whether it is worth asking.

If you have doubts, ask the city hall for the sunlight study in the building-permit file and compare it with what you see here.


## How many buildings in Bucharest have a height on the map?

OpenStreetMap does not know the height of every building. Of 138,158 buildings in Bucharest, 20% have a height or a number of floors. The ones that cast shade matter most: 80% of buildings tagged as apartment blocks and 55% of those over 400 m² have a height or a number of floors on the map.

For the others we use the median height of buildings of the same kind and size that do have a height or floor count (table below). In the 3D map, buildings with an estimated height are hatched. Under each window's result, the page says how many of the buildings forming its skyline have a recorded height or floor count and how many are estimated, and the ranges show how much the result moves if the estimates are wrong.

The rule: the height tag; if missing, 3 m for each level in building:levels; if both are missing, the median. Blocks are usually tagged, small houses and sheds rarely. Buildings with a recorded height tend to be the taller ones, so their median can exceed the true height of low buildings that have no tag.


## What the calculation does not know

These results are an estimate, not a measurement from inside your flat. What is missing:

- Trees. A locust or a linden in front of the window can shade more than a block, and it does not appear in the calculation.
- Balconies, loggias and window depth. A balcony above you or a side wall of a loggia shades the window and is not modelled. The calculation takes a single point on the facade, halfway up a storey.
- The exact position of the window. On a long facade the sun can reach the two ends differently. Click another spot on the wall and compare.
- Future buildings. The map contains the OpenStreetMap building footprints present in the 28 September 2026 extract. Whether a building appears depends on whether it was in that extract, not when construction started; you can add a missing one yourself with the new-block tool.
- Estimated heights. For buildings with no height or floor count on the map, the calculation assumes the median in the table and tells you how many there are.
- Roof shape. Every building is a box with a flat roof. A pitched roof casts less shade near the ridge.
- Terrain. Ground is assumed flat, which is close to true in Bucharest.
- Weather. The figures show how many hours of sun would be possible under a clear sky. Clouds are not included.
- Light in the room. Direct sun is one thing, daylight another. A room with no direct sun can still be bright.

## How the calculations work

The Sun. Its position for every minute of 2026 at the centre of Bucharest comes from the NOAA formulas (Meeus). We compared them with NASA JPL Horizons at 18 moments of the year, in the morning, at noon and in the evening: the largest difference is 0.005° in elevation and 0.012° in azimuth. At noon the Sun stands 22.1° high on 21 December, 45.5° on 20 March and 69.0° on 21 June, as 90° minus latitude plus declination predicts. Times are Bucharest clock times, with the move to summer time on 29 March and back on 25 October 2026. The Sun counts as visible when its upper edge, corrected for atmospheric refraction, clears the skyline of buildings.

The skyline. From the window point, the calculation casts rays in 2,880 directions (one every 0.125°) and finds, for each, the highest building edge on the ray within 1 km. The Sun is in shade when it is below that line. The window's own wall blocks every direction behind it.

The window. The point sits on the wall, 15 cm outside, 1.5 m above the floor of the chosen storey; one storey is 3 m. The shadows drawn on the map come from the graphics card and can differ by a few metres from the results, which come from the rays above.

Addresses. Search uses the street names and house numbers in OpenStreetMap, for a total of 151,074 addresses. 94% of address points fall on a building or within 30 m of one, and then we take the nearest building. If your address is missing or does not reach a building, click the wall.

Checks. A 30 m wall 65 m south of a window shades it at noon on 21 December, and at 95 m it lets the sun through; a north-facing wall gets no minute of sun on 21 December; a south-facing one under open sky gets 8 h 51 min.


## Sources

- OpenStreetMap contributors, Bucharest buildings (ODbL), extracted through the Overpass API on 28 September 2026 https://www.openstreetmap.org/copyright
- OpenStreetMap: the building:levels tag https://wiki.openstreetmap.org/wiki/Key:building:levels
- OpenStreetMap: the height tag https://wiki.openstreetmap.org/wiki/Key:height
- NOAA, solar position equations (Meeus) https://gml.noaa.gov/grad/solcalc/calcdetails.html
- NASA JPL Horizons, position of the Sun (the reference used for checking) https://ssd.jpl.nasa.gov/horizons/
- Romanian Ministry of Health Order no. 119/2014, article 3 (Official Gazette no. 127/2014) https://dspbihor.gov.ro/legislatie/OMS119%20din%202014.pdf