Give every room in which people spend time daylight from at least two sides; plan the building in narrow wings so that this is possible.
Rules · Site · Light · Roofs · Geometry
Size the overhang to the sun
On an equator-facing window, make the overhang deep enough to shade the whole window from the high noon sun of summer, and no deeper, so that the low winter sun passes beneath it into the room.
noon sun altitude = 90° − latitude ± 23.44° · overhang D = window height ⁄ tan(summer altitude)
At noon on the summer solstice the sun stands 23.44° higher than at the equinox, and at the winter solstice 23.44° lower; at latitude 51° (London) that is about 62° and 16°. An overhang sized to cut off the 62° sun at the sill leaves the 16° sun almost unobstructed, so the same glass that heats the house in winter is shaded in summer. The figure computes both angles and the overhang from the latitude; turn the latitude up toward the pole and the overhang shrinks, down toward the tropics and it grows.
The rule works best on windows facing the equator; east and west windows meet the sun low in the morning and evening and need vertical fins or planting instead.
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Cite this page Chris Paton, “Size the overhang to the sun”, The Textbook of Architecture, https://textbookofarchitecture.com/rule/solar-overhang. Text, drawings and models licensed under CC BY-NC 4.0.