Polyethylene film is worth considering when initial cost matters and the farm can accommodate periodic recovering. For a greenhouse heated through winter, the useful comparison is inflated double film against a specified multiwall polycarbonate panel. Glass belongs in the discussion when a permanent glazed structure suits the crop, and the budget covers its structure, heating and maintenance.
The growing calendar helps narrow that choice. A house used for a seasonal crop has a different job from one that must maintain temperature through winter nights. A break between crops may provide time to replace a cover; continuous production can make the same work difficult to schedule. Those details affect whether a lower purchase price remains attractive once the greenhouse is operating.
| Production or site condition | Covering to consider | The cost or constraint to resolve |
|---|---|---|
| Seasonal growing with limited initial funds | Greenhouse-grade film | Recovering labor, roof access and the break between crops |
| Regular winter heating | Inflated double film or specified multiwall PC | Heat transfer, air leakage and the required indoor temperature |
| A large roof that would be difficult to recover | Multiwall PC with a documented warranty | Installed cost, replacement-panel availability and access |
| A permanent glasshouse | Glass with its supporting structure and climate systems | Heating demand, glazing maintenance and the crop's light requirement |
| Strong wind or snow exposure | A cover compatible with the site-specific structural design | Foundations, frame, connections and cover supports |
Contents
Double film narrows the insulation gap
The difference between single film and inflated double film is large enough to change a buying decision. Alabama Cooperative Extension lists the following indicative heat transmission coefficients. A lower U-value means less heat transfer for the same area and temperature difference; the SI equivalents here are rounded conversions.
| Cover construction | U-value, Btu/(h·ft²·°F) | Equivalent U-value, W/(m²·K) |
|---|---|---|
| Single polyethylene film | 1.20 | 6.81 |
| Inflated double polyethylene film | 0.70 | 3.97 |
| 8 mm twin-wall polycarbonate | 0.65 | 3.69 |
| Single glass | 1.13 | 6.42 |
Source: Alabama Cooperative Extension, greenhouse environmental control, Table 2.
The PC coefficient in this table is approximately 7% below the double-film value: (0.70 − 0.65) / 0.70. That does not mean a 7% reduction in annual fuel use. Air leakage, surface area, temperature settings and other heat losses still enter the calculation. A project estimate needs the proposed products and the whole greenhouse design.
The film specification matters too. Where an infrared-retaining film forms part of a double covering, UConn Extension places it on the inner layer. The proposal also needs to explain how the air space will be kept inflated. UConn Extension, Plastic Film Update.
What a light-transmission figure actually tells you
Two percentages on competing quotations may measure different things. A single film's photosynthetically active radiation (PAR) transmission is not directly comparable with a complete double covering or a panel's visible-light transmission. The thickness, layer arrangement, diffusion properties and test method belong beside the number.
UConn gives typical PAR transmission of 88% to 91% for UV-stabilized film, with different ranges for films containing other additives. These are film values, before the rest of the greenhouse affects the light reaching the crop. UConn Extension, film light transmission.
Palram, for example, lists 80% light transmission and a U-value of 3.3 W/(m²·K) for its clear 8 mm SUNLITE twin-wall sheet. That thermal value differs from the generic extension figure above. The manufacturer's data applies to its particular configuration; a quotation for another panel needs its own specification. Palram SUNLITE specifications.
For crop planning, the next step is the available light during the limiting production month, allowing for the covering assembly, structural shading and screens. Material transmission alone cannot predict yield.
The cost of changing a cover
A film roll or PC panel is only part of a replacement job. Removal, freight, labor and roof access all need funding. The farm also needs someone able to do the work locally, replacement material that can be obtained, and a suitable point in the production calendar. For double film, inflation equipment and its electricity use belong in the operating budget.
UConn distinguishes short-duration film from greenhouse-grade polyethylene warranted for four years or more. Sunlight, heat, abrasion and installation conditions influence how long it remains serviceable. UConn Extension, film life and failure.
For SUNLITE, Palram advertises a ten-year limited warranty. Its terms and remedy need to be read for the product and market being quoted. Neither warranty sets a fixed replacement date, and the SUNLITE term cannot be applied to every PC greenhouse. Palram SUNLITE product information.
A film proposal becomes difficult to justify if recovering conflicts with continuous cropping and no workable access or labor plan exists. PC still needs a cost comparison: an assumed heating saving is too little to support its business case.
Compare complete installed offers over the same operating period, using matching dimensions, structural loads and environmental requirements. Include transport and installation exclusions as well as future replacement work. A universal payback period would conceal the local costs and energy assumptions that determine the result.
Wind and snow loads follow the structure
A rigid panel does not give an existing greenhouse a new structural rating. Palram's greenhouse installation manual relates panel spans to loading and support conditions, allows for thermal movement, and states that its span recommendations do not replace local construction-code requirements. Palram SUNLITE Plus greenhouse installation instructions.
For a new build, the site's wind and snow requirements should be the same in every bid. The designer needs to assess the frame and foundations together with the cover supports, fasteners and connections. Panel impact resistance is a separate claim from the load capacity of that assembly.
Can film be replaced with PC on the same frame?
It requires a retrofit assessment. Panel support spacing, fastening, thermal movement and the frame's capacity under the site's loads must suit the new cover. Any necessary modifications belong in the installed price. Without that design, a comparison with simply recovering in film is incomplete.
Glass needs its own operating plan
Single glass and insulated double glazing have different thermal and light-transmission properties. University of Wisconsin's greenhouse energy guidance distinguishes the two and identifies the heavier supporting structure associated with glass. University of Wisconsin, Energy Conservation for Greenhouses.
Glass deserves consideration where the complete structure meets the crop's light needs and the business can fund heating and glazing maintenance. Permanence should not be mistaken for insulation: the single-glass value in the table is considerably higher than the double-film value. If the installed glasshouse would use the money needed for essential climate controls, the proposal needs revisiting.
CFGET's glass greenhouse range and polycarbonate greenhouse range provide structural formats to compare once the growing requirements are defined.
Three published CFGET projects
The following project records show film, PC and glass used with environmental systems. Floor areas are calculated from the published length and width.
| Published project | Cover and application | Calculated floor area | Listed environmental systems |
|---|---|---|---|
| Tajikistan fruit-growing greenhouse | Film; fruit growing | 48 × 48 m = 2,304 m² | Cooling, ventilation and internal shading |
| Uzbekistan flower greenhouse | PC sheets; flowers | 48 × 36 m = 1,728 m² | Cooling, ventilation, internal and external shading |
| Italy flower greenhouse | Glass; flowers | 48 × 60 m = 2,880 m² | Cooling, ventilation, internal and external shading, intelligent control |
Cooling and ventilation appear in all three configurations. The records describe what was supplied; they do not contain comparable installed costs, energy use, crop results or the customers' reasons for choosing a cover. They are useful examples of configurations, without establishing a performance ranking.
Which covering would suit commercial tomatoes?
The production season and target growing conditions come first. Film, PC and glass proposals should each be assessed against the same light and temperature requirements. A large planting area does not rule out PC, just as a valuable crop does not automatically justify it. Paying more for a cover is not evidence of a higher tomato yield.
Discuss your growing plan
The project location, crop, growing months, area and target indoor temperatures give a covering discussion a useful starting point. For an existing greenhouse, include frame drawings and the time available between crops for maintenance. CFGET can then discuss covering configurations and the scope each proposal needs to include. Discuss your greenhouse project.
Published: 2024-08-16
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