Greenhouse Structures and Design
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. Greenhouse styles can vary from small stand-alone structures to large gutter-connected greenhouses. There are many designs and structures to select from, thus it is important to become familiar with the advantages and disadvantages of each.
These are single houses that have roofs with an even pitch and an even width (See Figure 1.1). They have pitched roofs like a house with straight sides and two gable ends. This type of structure is what one usually envisions when the word greenhouse is mentioned.
Typically uneven-span greenhouses are constructed on hilly terrain. The roofs are of unequal width; make the structure adaptable to the side slopes of hill (See Figure 1.2). This type of greenhouses is seldom used since it is not adaptable for automation.
Quonset-shaped greenhouses are constructed with bent pipe frames made of either metal or PVC (See Figure 1.3). The flexible trusses are often anchored into sturdy metal pipe foundations. They are covered with flexible plastic film, either a single or a double layer. A small fan usually provides air support for the double layer.
High Tunnel Greenhouses
High tunnels are similar in shape to quonset-type structures, but they aren’t heated and they aren’t considered permanent (See Figure 1.4). One of their unique features is that roll-up sides are used for ventilation and temperature control on sunny days.
A-frames have sloping sides all the way to the foundation, which makes them the best style for passive snow removal and limiting snow buildup (See Figure 1.5). Like hoop houses, they are relatively inexpensive and simple to build. Frames are often made from two-by-four lumber and are generally covered with a single layer of polyethylene film.
Gothic Arch Greenhouses
Gothic arch greenhouses have an arched roof line and walls that form a continuous shape (See Figure 1.6). Snow slides off them better than from a hoop house but not as well as from an A-frame. They have more headspace than an A-frame but not as much as a hoop house of similar height.
Gable-style greenhouses have sloping, flat roofs connected to vertical sidewalls (See Figure 1.7). The roof angle determines how well snow slides off as well as the total height of the structure. The well-defined roof line is adaptable to efficient roof-ventilation systems.
Ridge-and furrow-greenhouse structure consists of a number of even span greenhouses connected along the length of the house (See Figure 1.8). All shared walls are eliminated giving you more growing space. These houses are sometimes called gutter connected because gutters are installed where the houses are joined to help move water.
Barrel Vault Greenhouses
The barrel vault greenhouse consists of several Quonset type greenhouses connected through gutters (See Figure 1.9). An advantage is that they can be built with a ridge vent which provides air circulation throughout. A disadvantage would be that they are difficult to maintain.
The Netherlands developed a ridge-and-furrow structure called the “Venlo greenhouse” (See Figure 1.10). The galvanized steel superstructure supports a gable roof. It has a self-supporting glazing bar system. The bars are placed opposite each other, so less material is needed and more light is available. This type of greenhouse has the highest percentage of light transmission of any greenhouse presently on the market as well as the lowest roof surface area exposed, thus reducing the heating demand.
Sawtooth greenhouses consist of a series of lean-to greenhouses connected together (See Figure 1.12). Where sawtooth greenhouses were once considered an inexpensive construction design and covered with sheet plastic, they are now common to coastal regions and covered with more permanent glazing materials.
Click on the following topics for more information on greenhouse structures and design.