How to use this tool
- Set the place and direction. Enter your location and set the direction the balcony or window faces: the direction you look when you stand in it and look out.
- Describe the surroundings. Set the height of your floor, the buildings opposite (height and distance), the depth of any balcony or roof above, and whether the balcony has side walls.
- Read the result. The summary shows how many hours of direct sun the balcony gets on the selected day and when. The heatmap shows every hour of every month at a glance, and the bar chart gives the monthly totals.
- Check the 3D model. Drag the time slider to see exactly when the sun reaches the balcony and when the buildings opposite or the balcony above cast their shadow.
How the calculation works
For every few minutes of the day, the tool checks four things:
- Is the sun in front of the facade? The sun must be less than 90° to either side of the facing direction.
- Is it above the buildings opposite? Their roofline forms a raised horizon. The angle is arctan((their height − your floor height) ÷ distance).
- Is it below the overhang? A balcony or roof above blocks the sun when its height in the plane of the facade (the profile angle) is steeper than the angle from the bottom of the opening to the edge of the overhang.
- Is it within the side walls? For a recessed balcony, the side walls cut off sun that comes in too steeply from the side.
The result is for the foot of the opening: floor level at the window or balcony door, in the middle of its width. The outer edge of the balcony usually gets a little more sun, the back of the room less.
Worked example
A south-facing balcony 6 m above the ground in Ljubljana, with 15 m high buildings 20 m away and a 1.2 m deep balcony above. Around the equinoxes the sun reaches the balcony door all day. On the December solstice the low sun stays behind the buildings opposite, so it gets no direct sun at all. On the June solstice it also gets none, but for the opposite reason: the high summer sun is blocked by the balcony above. Set the balcony above to 0 and the summer sun returns; move up to the fifth floor and the winter sun returns. This is exactly how a well-designed south facade keeps rooms warm in winter and cool in summer.
Hot balconies
West- and south-west-facing balconies get strong afternoon sun in summer, when the air is already warm. If the tool shows more than three hours of direct sun between about 13:00 and 19:00 in summer, plan for an awning, external blinds or plants for shade. The guide which direction does my house face explains what each orientation means.
Last updated September 23, 2026