Film plastic coverings are available in several grades of quality and several different materials. Generally, these are replaced more frequently than other covers. Structural costs are very low because the frame can be lighter and plastic film is inexpensive. A utility grade of PE that will last about a year is available at local hardware stores. Commercial greenhouse grade PE has ultraviolet inhibitors in it to protect against ultraviolet rays and it lasts 12 to 18 months.
Copolymers last two to three years.
The heating requirement of a greenhouse depends on the desired temperature for the plants grown, the location and construction of the greenhouse and the total outside exposed area of the structure. The heating system must be adequate to maintain the desired day or night temperature. Heating systems can be fueled by electricity, gas, oil or wood. The heat can be distributed by forced hot air, radiant heat, hot water or steam. For safety purposes and to prevent harmful gases from contacting plants, all gas, oil and woodburning systems must be properly vented to the outside.