Passive Solar Design
This pattern is shaped by
Problem
When a building's orientation, glazing, and mass are designed without reference to the sun's path, the occupants pay twice: once in winter, when solar heat that could warm the rooms for free is lost to poorly placed windows and uninsulated walls, and again in summer, when west-facing glass traps unwanted heat that mechanical systems must remove. The building fights the sun instead of working with it.
Evidence and Discussion
The physics are ancient and exact. At Edmonton's latitude (53.5°N), the winter sun rises at azimuth 127° and sets at 233°, reaching a maximum altitude of only 13° at the December solstice. By June, it rises at 37° azimuth, peaks at 60° altitude, and doesn't set until nearly 10 p.m. A vertical south-facing window receives 5.5 times more solar radiation in December than in June — nature's own thermostat, if the building is designed to use it. The Passive House Institute's monitoring of over 4,000 certified buildings across climate zones confirms that properly oriented structures with calculated solar apertures reduce heating energy by 75-90% compared to code-minimum construction.
The key variables are solar heat gain coefficient (SHGC), glazing area, thermal mass, and shading. Edward Mazria's *The Passive Solar Energy Book* (1979) established the foundational ratios still used today: south-facing glazing should equal 7-12% of floor area in cold climates, backed by thermal mass capable of absorbing and releasing the day's solar gain over 12-16 hours. The Saskatchewan Conservation House, built in Regina in 1977, demonstrated these principles at 50°N latitude — triple-glazed south windows, a concrete floor slab, and super-insulation achieved 85% heating energy reduction in a climate with 5,700 heating degree days. Forty-seven years later, the building still performs as designed.
Modern passive solar buildings have refined these ratios with better glass and tighter envelopes. The Mill Creek NetZero Home, built in Edmonton in 2007, orients its main glazing 15° east of true south to capture morning gain when heating loads peak after cold nights. Monitoring by the Alberta Research Council showed the 220 m² house required only 15 GJ/year for space heating — one-sixth the Edmonton average for homes of similar size. The glazing-to-floor ratio was 9.2% on the south face, with a concrete slab floor providing 22 kJ/°C·m² of thermal capacitance. Summer overheating was controlled by a 600mm roof overhang that blocks direct sun when the altitude exceeds 55° (May through August).
Alexander identified these forces in Pattern 105 (South Facing Outdoors) and Pattern 106 (Positive Outdoor Space), but wrote before the oil crises prompted systematic research. The evidence now spans thousands of buildings across cold climates: Vorarlberg, Austria's social housing program has built over 300 passive solar multi-family buildings since 1995, averaging 15 kWh/m²·year heating demand. Norway's Powerhouse Brattørkaia, completed in 2019 at latitude 63°N — ten degrees north of Edmonton — generates more energy than it uses annually, with 55% of its heating provided by passive solar gain through calculated south glazing.
Therefore
Orient the building's long axis within 15° of east-west. Place 7-12% of heated floor area as south-facing glazing (SHGC ≥ 0.5 in cold climates), with thermal mass — a minimum of 100 kg per square meter of south glass — positioned where direct sun strikes it. Size roof overhangs or exterior shading to block direct sun when solar altitude exceeds 50° (Edmonton: May 1 to August 15). Test the design with hourly energy simulation: a properly configured passive solar building at 53°N should achieve at least 40% of its heating load from direct solar gain on a clear January day.