Section 3: Other Glazing Materials
Other potential greenhouse glazing materials exist. Among these are polyvinyl chloride, weatherable polyester film and polyvinyl fluoride film. However, either because of their properties or their cost, they are not commonly used in commercial greenhouse situations.
Colored Glazing Materials
Certain glazings may have pigments added (polyethylene films) or may be filled with colored liquid (polycarbonate bi-wall panels) to adjust the spectral transmittance (light quality) allowed to pass through the glazing. The principle behind behind such glazings is that by altering the quality of light the plants experience, plant growth and development can be manipulated. For example, when grown under an environment rich in red versus far-red light, or under an environment high in blue light, plants should grow shorter and stockier and thus have less need for plant growth retarding chemicals. However, in commercial practice, these types of glazings have not been extensively used. More discussion of colored glazings and light quality effects on plants may be found under the “Lighting” learning unit.
Table 1. Some Common Greenhouse Glazing Materials and Their Typical Properties |
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Glazing |
Light transmittance (%) |
U factor |
R value |
Estimated life span (years) |
Estimated cost / ft2 |
Standard glass single 3 mm pane |
90 |
1.05 |
0.95 |
25+ |
$6.00 |
Double strength glass |
88 |
1.1 |
0.91 |
25+ |
$3.00 |
Insulated glass |
78 |
0.70 |
1.43 |
25+ |
$6.00 |
Single layer polyethylene |
85 |
1.2 |
0.83 |
1 to 4 |
$0.085 |
Double layer polyethylene |
77 |
0.70 |
1.43 |
1 to 4 |
$0.170 |
Fiberglass reinforced polyester (untreated) |
90 |
1.0 |
0.90 |
2 to 3 |
$1.25 |
Acrylic twin wall high impact (8 mm) |
84 |
0.56 |
1.78 |
20+ |
$4.07 |
Acrylic twin wall high impact (16 mm) |
86 |
0.49 |
2.04 |
20+ |
$5.67 |
Polycarbonate twin wall (8mm) |
80 |
0.56 |
1.64 |
20+ |
$1.66 |
Polycarbonate twin wall (10mm) |
80 |
0.53 |
1.79 |
20+ |
$2.50 |
Polycarbonate double layer (16mm) |
72 |
0.42 |
2.38 |
20+ |
$4.00 |
Polycarbonate corrugated panel |
91 |
1.2 |
0.83 |
20+ |
$1.30 |
Values are as examples only. Values are averages developed from various company sources. Cost values are for 2009 and are estimates and do not include volume discounts nor costs for mounting. Different brands of glazings may have somewhat different U and R values. |
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