Horticulture Principles and Practices

12.2.3 FRAME DESIGN
There are two basic frame designs: A-frame (gabled) and arched-frame greenhouses
(curved arch). The gabled types are more expensive to construct.
A-Frame Greenhouses
In A-frame design, most of the weight of the greenhouse rests on the side posts, which
are often encased in concrete. These erect posts support the truss (consisting of rafter,
strut, and chords). The trusses on either side meet at the peak (ridge) of the roof. Series
of trusses are connected by long bars (purlins) that run the length of the greenhouse. The
end view presents an A-shaped structure called a gable (Figure 12–11). The bottom 2 to
3 feet (0.6 to 0.93 meters) of the greenhouse above the ground consists of a wall called
the curtain wall, which is made out of materials such as cement or concrete blocks. The
curtain wall is the structure to which heating pipes are usually attached. Sash bars are
attached to purlins as anchors for panes.
Arched-Frame Greenhouses
In arched-frame greenhouse designs, the trusses are pipes that are bent into an arch and
connected by purlins (Figure 12–12). This design is called a Quonset.
12.2.4 GLAZING (COVERING) MATERIAL
The most important role of glazing or covering material is transmittance of light. No
material can transmit 100 percent of all of the light that strikes its surface. It is hoped that
most of the light will be transmitted through the material, but some of it will be absorbed
or reflected back into the atmosphere. The materials used for glazing are described in the
Glazing
A transparent material
used to cover a
greenhouse frame.
Purlin
Ridge
Ventilator
Header
FIGURE 12–11 A-frame
greenhouse structure: (a) end
view and (b) general view.
Eave
Rafter
Strut
Chord
Side post
Curtain wall
(a)
Ground level
Footer
Ridge
Ventilation
Strut
Vent header
Rafter
Purlin
Eave
Curtain wall
(b)
12.2 Greenhouse Design and Construction 395