Q+A with Caleb Johnson of Caleb Johnson Architects and Builders about the benefits of solar shades
Nick and Molly LaVecchia’s home (Small Footprint, Big Impact, page 110) in Scarborough is a 1,000-square-foot passive solar home. Heated with a heat pump powered by the solar panels, the home generates as much energy as it uses. Designed and built by Caleb Johnson Architects and Builders, it relies on solar shades to optimize the performance of the passive solar siting.
Q. What are solar shades?
A. Solar shades allow the sun in during the winter heating season when it’s needed and block it during peak times of heat gain in the summer. The shades on this house are wood structures made of eastern white cedar that hang above the south-facing windows at a calculated height. In Maine’s latitude, a 10-foot-high window usually requires a 21⁄2-foot-deep shade. They are about 19 feet in length and cost about $2,000 in materials and labor. Constructed of wood fins set at an angle so the rain and snow can pass through, they provide a modern- aesthetic alternative to blinds or awnings.
Q. How do they work?
A. Solar shades are a critical piece of a passive solar home. Passive solar homes capture energy from the sun in the daytime and drive that energy into some form of thermal mass such as a concrete floor. In winter, solar shades allow the sun in to heat the thermal mass, which then releases that heat in the evening. In summer, the shades block the sun during the daytime. Opening the windows at night cools the thermal mass, which then cools the house during the day.
Q. Why are solar shades a better option than blinds or overhangs?
A. For homes in New England, the geometry of overhangs doesn’t always fit all needs: while a farmer’s porch, which is generally 10 to 12 feet deep, blocks the summer sun, it’s too deep to allow solar gain in winter. Blinds can obstruct the view out the window. Finally, it’s more effective for a shade system to be on the exterior of the building envelope so it doesn’t hold heat inside the house.