Calculate optimal passive solar roof overhang and eave projection depth to block 100% of blistering summer sun while admitting 100% of warming winter rays.
Bioclimatic Solar Architecture: Passive Eaves Engineering
Windows are thermal conduits. In summer, direct sunlight radiating through standard double-pane glass injects roughly 200 to 250 BTUs per square foot per hour into a room, dramatically overloading air conditioning systems. In winter, that exact same solar aperture serves as a free, non-polluting furnace.
Solar Noon Altitude Equations
Summer Solstice Noon Angle = 90° - Latitude + 23.45°
Winter Solstice Noon Angle = 90° - Latitude - 23.45°
Overhang Depth = Total Drop Height / tan(Summer Sun Angle)
Because the earth's tilt angle oscillates by $\pm 23.45^\circ$, the seasonal sun height differential at solar noon is always a massive 46.9 degrees. Designing fixed overhangs tailored to this astronomical constant provides lifelong thermal comfort with zero mechanical moving parts.
Frequently Asked Questions
What is thermal lag and why does August feel hotter than June?
Solar radiation peaks on June 21 (Summer Solstice), but the Earth's oceans and landmass take several weeks to absorb and re-radiate this heat. Consequently, the hottest ambient air temperatures typically occur in late July and August. Sizing overhangs for late summer ensures shading when cooling loads peak.
Can overhangs shade East and West facing windows?
Horizontal overhangs only shade windows when the sun is high overhead (South-facing midday). On East and West facades, the morning and afternoon sun is low to the horizon and beams directly beneath roof eaves. Use vertical fins, exterior solar screens, or deciduous trees for East/West shading.