Designing and building a greenhouse may be every gardener’s dream, but it can be a costly and complex affair. One of the main considerations, affecting both cost and durability of the greenhouse, is the material to cover the greenhouse. PVC film and polycarbonate panels correspond to different approaches to building a greenhouse.
PVC Plastic Coverings
Sheets of clear PVC plastic are the least expensive option for covering a greenhouse. The greatest downfall is their short lifespan -- typical 6 mil plastic from a hardware store lasts only a year or two. Special greenhouse plastics last longer and are available from greenhouse supply companies. Sheets of PVC plastic draped over a structure of PVC pipe “hoops” make a functional greenhouse that can be assembled in a few hours with a modest budget.
Polycarbonate Roofing Material
Rigid polycarbonate panels are generally rated for 10 years of use, but are costly. They have better light transmission than plastic, though this diminishes over time, unless they are treated to prevent the discoloration that naturally occurs. Polycarbonate panels are rectangular and moderately flexible, allowing them to be used on a curved frame. Most polycarbonate products are double-layered with space in between the layers that gives superior insulation compared to PVC films.
PVC film is a good choice for a temporary greenhouse, or as an interim covering before a more permanent material is installed. Hoop-style greenhouses, wood frame structures, domes and prefabricated-metal frame greenhouse kits are all amenable to PVC coverings. If you want to use polycarbonate panels, the frame of the structure must be designed to match the dimensions of the sheets. The spacing of roof rafters and wall studs should correspond to the width of the panels and you need special hardware to attach them to the structure and seal the seams between them. PVC pipe hoop-style greenhouses are not an option with rigid polycarbonate coverings, but almost any other greenhouse style is possible if designed correctly.
One common approach is to combine PVC film and polycarbonate panels on a greenhouse, to take advantage of the best properties of each and minimize costs. This is most common with Quonset-style greenhouses, which are tunnel-shaped structures. The PVC film covers the hoop-shaped roof and side walls, while polycarbonate panels are used on the vertical end walls. Permanent doors and vents are built into the polycarbonate walls and the PVC sides are typically designed to roll up and down for ventilation.
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