Shading — the prevention of unwanted solar gain on south, east, and west glazing during the summer — is as important as solar gain in winter. A south-facing building without adequate summer shading will overheat in most climates, regardless of thermal mass.

The most elegant shading solution is the roof overhang, sized to shade the south glazing during the summer months (when the sun is high) and admit sunlight during the winter months (when the sun is low). The geometry of this calculation is straightforward: knowing the sun’s altitude angle at the summer solstice and the winter solstice at your latitude, you can calculate the overhang depth required to shade the glazing in summer and expose it in winter. Book 4 of this series includes detailed worked examples and tables for common latitudes.

East and west glazing is more difficult to shade with fixed overhangs because the sun’s angles in the morning and afternoon are low and from the side rather than overhead. Vertical fins, recessed windows, landscaping, and operable shading devices (awnings, roller shades, exterior shutters) are the most effective solutions for east and west exposures. Minimizing east and west glazing in the first place is the most reliable strategy: a building whose long axis runs east-west and whose primary glazing faces south has inherently less problematic east and west exposure than a building oriented otherwise.

Review Questions

1. Describe the three pillars of passive solar design and explain how each contributes to the system. What happens to the performance of a passive solar building if one of the three pillars is inadequate?

2. What is the difference between a direct gain passive solar system and a Trombe wall? What are the advantages and disadvantages of each?

3. How does thermal mass work? What materials have high thermal mass, and what determines how effective a given piece of thermal mass is in a passive solar building?

4. Describe two mechanisms by which natural ventilation moves air through a building. What does the building design need to provide to enable each mechanism?

5. Why is a fixed roof overhang on the south face of a building effective for seasonal shading? What determines the correct depth of the overhang for a given location?