Sustainability Learning Lab at Bellevue University

Greenhouse, also called glasshouse, is a building designed for the protection of tender or out-of-season plants against excessive cold or heat. In the 17th century, greenhouses were ordinary brick or timber shelters with a normal proportion of window space and some means of heating. As glass became cheaper and as more sophisticated forms of heating became available, the greenhouse evolved into a roofed and walled structure built of glass with a minimal wooden or metal skeleton. By the middle of the 19th century, the greenhouse had developed from a mere refuge from a hostile climate into a controlled environment, adapted to the needs of particular plants.
The modern greenhouse is usually a glass- or plastic-enclosed framed structure that is used for the production of fruits, vegetables, flowers, and any other plants that require special conditions of temperature. The basic structural forms are the span-type greenhouse, which has a double-sloped, or A-shaped, roof, and the lean-to greenhouse, which has only one roof slope and leans against the side of a building. Two or more span-type greenhouses are sometimes joined side by side so that they have fewer external walls, and heating costs are consequently less. A greenhouse has a large expanse of glazing on its sides and roof so that the plants are exposed to natural light for much of the day. Glass has been the traditional glazing material, but plastic films, such as polyethylene or polyvinyl, and fibreglass are also common..The framing of the structure is made of aluminum, galvanized steel, or such woods as redwood, cedar, or cypress. A greenhouse is heated partly by the rays of the Sun and partly by artificial means, such as circulating steam, hot water, or hot air. Because a greenhouse can become too hot as well as too cold, some type of ventilating system is also needed; this usually consists of roof openings, which can be operated mechanically or automatically, and end-wall openings, through which electric fans draw air and circulate it throughout the interior.

Source: The Editors of Encyclopaedia Britannica

______________________________________________________________________________________________________________

Click on image for a larger view and and more information

Source:Agritecture website