When choosing a greenhouse, one question which must be answered is what sort of covering do you want? There are four basic choices for greenhouse covering materials; glass, fiberglass, polycarbonate, and polyethylene film. Each has their advantages and disadvantages.
Glass is the traditional greenhouse covering and has been used for hundreds of years. Glass is generally the most attractive and permanent, material, barring hailstorms. Glass on a greenhouse will never need to be replaced, barring breakage. Glass is the best light transmitter of the available materials, transmitting 93 - 95% of available light. But glass has virtually no insulating value, allowing heat to escape at night very quickly. Glass does not diffuse sunlight, which can cause hotspots within a greenhouse, damaging plants. It allows a lot of heat into the greenhouse on a sunny day, perhaps causing overheating. Even in winter, this can happen and damage plants. Glass is heavier, increasing shipping costs and construction costs, as it will need a more substantial framework than plastics.
Fiberglass was the first material which was a practical substitute for glass as a greenhouse covering. Its light transmission is just about as good as glass, but because it is translucent, it tends to diffuse light. This creates even distribution of light and makes a shadow less greenhouse. Fiberglass retains heat better than glass, and will transmit less heat into the greenhouse, reducing the risk of overheating. Fiberglass has a gel coating on it which, after about six years or so, will be baked off by the sun. The fiberglass will yellow at this point and become very unattractive.
Polycarbonate is the newest material available for covering greenhouses. It is just about as clear as glass, is available in several thicknesses and can be purchased in single, double, or triple walled sheets. The extra walls add strength and insulating qualities to the sheet. Polycarbonate lasts a long time, usually twelve years or more, and has greater impact resistance than other materials. Its light diffusion qualities are good, transmitting about 85% of the available light. Polycarbonates are used in most of the kits available now.
Polyethylene films are the most popular greenhouse film currently. It is used in over 90% of existing greenhouse structures. It has good light transmission qualities, has good heat retention qualities and is similar to fiberglass in its light diffusion properties. Because it is so pliable, it is adaptable to just about any type of framework and its light weight allows its use on a lightweight frame. Shipping costs are also low for this film. Commercial growers like it because it is easily installed, replaced, is fairly cheap when compared with other coverings, and is easy to maintain. When double layered and inflated with a fan, the insulating qualities are very good. But, it lasts only three to five years and is easily ripped.
The choices in coverings for a greenhouse are many and may make it hard to choose. But one will suit your situation better than the others.
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