Solar Shading Overhang Calculator
The overhang depth that shades a window at the summer solstice while letting the winter sun in — the geometry of passive solar design, from latitude and window height alone.
The sun's noon altitude on the solstice is 90° minus your latitude plus or minus 23.
How the solar shading overhang calculator works
The sun's noon altitude on the solstice is 90° minus your latitude plus or minus 23.4°. An overhang shades the full window when its depth is the window height divided by the tangent of the summer altitude, and it lets winter sun reach the sill when the depth is less than the same thing at the winter altitude.
At latitude 35° that is a depth about 0.43 times the window height — the classic passive-solar proportion for an equator-facing wall.
Formula: depth = window height / tan(summer noon altitude); altitude = 90° − latitude + 23.4°
Worked examples
| Inputs | Overhang depth for full summer shade (m) | Note |
|---|---|---|
| Latitude 35, a 2.1 m window | 0.491 | about 1.0 m |
| Tropical | 0.356 | a shallower overhang shades a high sun |
| High latitude | 1.474 | needs a deep overhang |
FAQFrequently asked questions
How deep should an overhang be?
For full summer shade on an equator-facing window, about 0.4 to 0.5 times the window height at mid-latitudes. The exact figure is the tangent of the summer sun angle.
Why does it let winter sun in?
Because the winter sun is 47° lower than the summer sun. An overhang sized for summer shade lets most of the low winter sun under it — that is the whole trick of passive solar.
Does this work on east and west windows?
No — the sun is low on those faces morning and afternoon regardless of season. They need vertical fins or external blinds, not overhangs.
Which hemisphere?
Either — the geometry is symmetric. Enter latitude as a positive number and apply it to the equator-facing wall: north in the south, south in the north.
What about the solstice being the wrong target?
Many designers size for a date in the shoulder season instead, accepting some early-summer sun to gain more in autumn. Adjust the latitude by a few degrees to approximate that.
Where these figures come from
- Sabine (1922) — Collected Papers on Acoustics — the reverberation-time equation
- CIBSE Guide A — Environmental design — daylight, comfort and ventilation criteria
- Neufert — Architects' Data — the standard reference for space and dimension
- International Code Council — International Building Code — occupant load and egress factors
- Australian Building Codes Board — National Construction Code — the body that writes Australia's building code
Last checked: September 2026. Formulas are the standard building-science and code relationships; default thresholds are common international values and should be replaced with the ones in your code.