Editor’s Note: Dr. Kacira is an associate professor in the Agricultural and Biosystems Engineering Department and Controlled Environment Agriculture Center at the University of Arizona.
Many elements must be taken into consideration when choosing the type of greenhouse to construct. Numerous factors for greenhouse design and technology selection must be looked at before building. Some things to consider include: market size and infrastructure in the region; climate of the site; plant requirements; water quality and accessibility; cost of land; zoning restrictions; availability of materials, equipment, and services; accessible labor source; and capital availability for investment, economics, and marketing.
The anticipated production quantity and quality also play a role when selecting a design. A reasonable balance needs to be established based on market demand, grower skills, expected economic return, and level of greenhouse technology selected for crop production.
Greenhouse styles can vary from small stand-alone structures to large gutter-connected greenhouses. Greenhouse designs can be simply classified as attached (i.e. lean-to), free standing (i.e. even-span, uneven span, Quonset, arch), and ridge-furrow or gutter connected (i.e. sawtooth, venlo). There are many designs and structures to select from, thus it is important to become familiar with the advantages and disadvantages of each. Here is a brief rundown of some of the styles available to growers.
Free Standing Styles
Free standing greenhouses are either an A-frame type or feature an arch/curvilinear roof shape. Arch roof structures provide good light transmission and are less costly to construct than peak-roof structures. Arch-roof greenhouses (also known as gothic) are also adaptable to both rigid and flexible glazing materials.
Arch-type structures can be modified into several designs. For instance, Quonset greenhouses when designed low to the ground can be used as cold frames for nursery purposes or as high tunnel greenhouses for vegetable production. The glazing is usually plastic. Quonset sidewall height is low, which can restrict storage space and headroom. This type of greenhouse can be placed on columns, enabling plants to grow taller to meet crop requirements.
The gothic-type greenhouse is similar to that of the Quonset but it has a “gothic” shape, featuring an arch and a pointed ridge. This shape allows more headroom at the sidewall than does the Quonset, and it can prevent snow build-up on the roof in colder climates.
Ridge And Furrow Styles
The ridge and furrow type greenhouse consists of a number of even span greenhouses connected along the length of the greenhouse. All shared walls are removed providing more growing space. These greenhouses are sometimes called gutter-connected. The ridge and furrow configuration is applicable to most of the commercial style greenhouses used for floriculture and vegetable production.
Gutter-connected greenhouses are less expensive to build, conserve ground area, and require less heating cost per ground area compared to stand-alone structures. In addition, gutter-connected greenhouses have less roof and wall area relative to floor area, so they are more energy-efficient. There are some disadvantages, however, including reduced light due to shadow from eaves and other structural elements, and snow accumulation over the eaves.
Another modified version of a ridge and furrow greenhouse is the Venlo style. The gable ends of Venlo structures are very narrow. The slim gable end allows for thinner bar use, and wider, single panes of glass glazing to be used on the roof. The Venlo style construction allows improved light transmission, enabling a high percentage of winter light to reach the crop. These structures originate from Dutch horticulture and are used widely in the Netherlands; however, they are also adopted by growers in Northern climates where reduced winter sunlight tends to be a limiting factor for crop growth.
Retractable Roof Or Open Roof
Designed as flat roof or A-frame type, retractable roof greenhouses can be used for basic protection of crops or as a complete crop production system with stationary or retractable insect screening, curtains for shading, heat retention, and perimeter walls with roll-up curtains with insect screening. They can allow the grower to open the structure completely or partially, providing higher rates of ventilation as well as more light for the crop. Generally used for ridge-furrow style structures, retractable-roof greenhouses have minimal climate control.
Offering the best of both worlds, open-roof greenhouses provide a natural environment for crops when the outside climate is suitable, and provide an artificial and protected environment when the outside is too cold or hot for crop production. Greenhouse air temperature can be maintained within one or two degrees of outside temperature with minimal or no energy required.
Often used by growers of perennials, baskets, and other potted plants, the plants can be hardened off during spring by opening the roof when the outside weather is suitable. This can save labor for moving plants outside. High winds or rain can prevent opening the roofs for cooling or ventilation, so adding side vents could help.
For improved crop production and quality, a careful selection of greenhouse structure, glazing, and climate control system is required. All greenhouses should be designed properly to withstand all possible load factors for safety and proper functionality purposes. The National Greenhouse Manufacturers Association (NGMA) publishes standards that gives guidance for determining design loads for greenhouses.
For more information, go to www.ngma.com.