Using Attached Sunspaces in Passive Solar Design

Increase home heating and cooling performance and boost savings quickly by adding attached sunspaces to existing structures.

| April 14, 2014

All glass sunspace

Fig. 4-6: Attached sunspaces are an easy way to retrofit a home for passive solar, although they often don’t perform well. This all-glass attached sunspace must be covered during the late spring, summer, and fall to prevent overheating. All-glass attached sunspaces also tend to lose lots of heat at night and therefore must be isolated from living spaces by doors.

Photo by Dan Chiras

Homeowners scramble to cut utility bills and find alternatives to fossil fuels as the prices of oil and natural gas continue to rise. The Homeowner’s Guide to Renewable Energy (New Society Publishers, 2011), by Dan Chiras, offers excellent ways to improve energy efficiency by making the switch from fossil fuels to clean, affordable, renewable energy. The following excerpt from “Free Heat” discusses the use of attached sunspaces in passive solar design.

You can purchase this book from the MOTHER EARTH NEWS store: The Homeowner’s Guide to Renewable Energy.

Types of Attached Sunspaces

The final option for passive solar design is the isolated gain system, more commonly referred to as the attached sunspace or solar greenhouse (Figure 4-4c). Attached sunspaces are passive solar heat collectors built onto the side of buildings. They are heated by the sun; the heat they generate is then transferred to adjoining rooms. Hence the term, isolated gain. (Heat is gained in an isolated space.)

Attached sunspaces are relatively easy to build onto many homes, provided there’s adequate solar exposure. All-glass attached sunspaces are available in kits, and there is no shortage of installers who can put one in for you. Unfortunately, this design is fraught with problems.

All-glass designs — that is, attached sunspaces with glass walls and glass roofs — tend to overheat in the summer and fall, causing severe discomfort in the home. They may even overheat in the winter. But isn’t this structure designed to collect heat and transfer it to the house in the winter?

Absolutely, but don’t expect to be able to use the space for much else. Overheating renders the sunspace much too hot to enjoy during daylight hours in the winter. Moreover, all but the hardiest of plants (cacti and succulents) find the intense heat oppressive. Most plants need to be kept below 85°F (29°C) for optimal growth; photosynthesis grinds to a halt at 100°F (37°C).

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