Orientation: The Most Important Passive Solar Decision

Building orientation is the most impactful single decision in passive solar design. Passive solar pioneer Doug Balcomb famously observed that “orientation is 80 percent of passive solar design.” Once a building is oriented correctly, all other passive solar strategies — glazing sizing, thermal mass, shading — work together to amplify its performance. A building oriented incorrectly cannot be adequately corrected by any amount of thermal mass or glazing optimization.

In the northern hemisphere, the primary solar glazing surface of a passive solar building should face true south. In practice, up to 20 degrees east or west of true south is acceptable without significant performance loss. Orienting the building’s long axis east-west maximizes the south-facing wall area and minimizes the east and west exposures, which receive low-angle morning and afternoon sun that is difficult to shade in summer.

Pangea generally recommends orienting buildings approximately 13.5 degrees east of magnetic south. This allows the building to capture the morning sun, which is valuable in cold climates because the building has been losing heat all night and benefits from early solar gain. The east bias also means the building’s primary south glazing reaches peak solar gain earlier in the day, before the afternoon temperature peak — useful for thermal management in hot climates.

Note that magnetic south and true south differ by an amount called magnetic declination, which varies by location and changes over time. For precise solar design, always work from true south, not magnetic south.