Detached greenhouses stand independently from one another. However, they may be connected to a work area or access another greenhouse through a corridor. The most common type of detached greenhouse for commercial production is the Quonset. These houses are constructed from arched rafters and usually have solid end walls for additional support. Quonset greenhouses are suitable for the production of most crops, but the growing area is somewhat restricted near the side walls. This reduces efficiency as well as productivity.
Ridge and furrow greenhouses are connected at the eave by a common gutter. Generally an internal wall below the gutter is not present allowing for increased efficiency. Ridge and furrow greenhouses may be gabled or curved arch. Gabled houses are usually suitable for heavy coverings (i.e. glass, fiberglass) while curved arch houses are covered with lighter materials (i.e. polyethylene, polycarbonates). Several connected ridge and furrow greenhouses are often referred to as a “range”.
Rafters are the primary vertical support of a greenhouse (Figure 2). They are generally placed on 2, 3, or 4 foot centers depending on strength requirements. Rafters may be of the truss type, or curved arch depending on the width of the greenhouse. Generally speaking, greenhouses over 50 feet wide require a reinforced truss construction.
Greenhouses may be constructed from several different materials. Among the most popular are aluminum, steel and wood. Of these three, aluminum is by far the most economical and longest lasting. Aluminum may be extrude in various shapes and thicknesses. This material can then be formed into rafters, side posts and other structural components.
Greenhouse coverings must be clear enough to provide optimum light transmission and at the same time be durable as well as economical. Several materials have been developed to meet these needs on a commercial basis.
Glass provides the best light transmission for greenhouse production. However, the structural components required to support glass are costly. Also the initial investment as well as the necessary maintenance has restricted the use of glass houses by Texas producers.
Fiberglass is another covering material that is frequently used on commercial greenhouses. Fiberglass is ridged, extremely durable, and does not require the extensive structural components of a glass house. Unfortunately, fiberglass is very susceptible to break down by ultra violet (UV) light. This causes the fibers to swell resulting in a significant decrease in light transmission. The life span of fiberglass can be as short as five years under certain conditions.