A solar greenhouse is different from a sunspace. One is designed to suit the needs of plants, the other those of people. A solar greenhouse is a pleasant place to visit, and it helps heat the house it's connected to, but these aren't its primary purposes.
Solar Greenhouse Design and Construction
The solar greenhouse design guidelines that follow are for the design of a solar greenhouse where light, not heat, is the limiting factor for plant growth. A greenhouse built to these parameters will require a small amount of back-up heat to maintain optimum growing conditions. Still, it will provide more energy to the house on an annual basis than it will require for occasional auxiliary heating.
(For a thorough discussion of design considerations for various types of greenhouses and sunspaces and a complete explanation of building methods, see The Homeowner's Complete Handbook for Add-On Solar Greenhouses and Sunspaces, by Andrew M. Shapiro, Rodale Press, 1985; $19.95.)