One of the most important decisions you must make is the choice of material to cover your greenhouse. You will want a material that will let in the maximum amount of light while allowing the least amount of heat to escape. As well it must be strong enough to withstand hail and heavy snow loads. Greenhouse glazing has improved remarkably in recent years. In addition to glass there is a wide range of plastic glazing in the form of film sheeting and rigid panels. You may be confused by the many trade names for each type of plastic. Discuss your options with a reputable greenhouse supplier or builder, and make sure the plastic is for greenhouse.

The traditional covering for greenhouses, glass is the preferred material for permanence. It lasts indefinitely although it does become brittle with age. Since glass is breakable it is more difficult and dangerous to install, it also requires a much sturdier frame than plastic covered greenhouses. Glass has undergone many improvements in recent years. Among the most important is increased strength (double and triple strength ratings) to resist breaking. Larger panes are also available; because fewer structural members are needed, more light can enter the greenhouse. Frosted and hammered panels can be used break up the light rays for more even distribution. Other advances have cut down on heat loss. Double-walled tempered glass reduces it by about one third. Low-emissive, or low-E, coating, is another option; it reduces heat loss without a corresponding loss of light. In addition to being energy efficient, low-e glass reduces condensation, partially blocks ultraviolet rays, and makes the inside glass warmer to the touch.

A greenhouse covered with film plastic is one sixth to one tenth of the cost per square foot of a glass covered structure. Although less permanent than glass, film plastic can be heated as efficiently as glass. Previously, film plastic had a life span of about three months in summer and nine months in winter. Newer, clear types that resist yellowing last three to five years and allow up to 89% light transmission. Sold under many trade names, they are available in many thickness from 2 mil to 15 mil. The thicker the film, the more expensive it is. Weather- resistant polyethylene film plastic, 4 mil thick is perhaps the least expensive film plastic that makes a satisfactory covering for a hobby greenhouse. In choosing  plastic film make sure you buy one that has UV protection. You can also buy a plastic film with an infrared inhibitor; it cuts heat loss inside the greenhouse by up to 20% on a cloudless night. Another way to reduce heat loss is to double- layer the plastic creating an air pocket for insulation. This space can be 3/4 to 4 inches thick. Although there is some light transmission loss, heating costs are reduced by one third. Another innovation in film covering is an anti condensate additive that allows moisture buildup to run down the sides of the film instead of onto the plants. By removing the condensation drops that block the sun's rays, this new type of film plastic allows more light into the greenhouse. In addition, it helps stop disease infection by keeping contaminated moisture from dripping on the plants.

These coverings, which include fiberglass, acrylic, and polycarbonate, come in corrugated and flat forms. Shatterproof, they resist hailstone damage to varying degrees (polycarbonate being the strongest). Some types of rigid plastics get dirty and do not quite let the same amount of light in as glass does. However a good wash with detergent  and water to remove dirt or smudges. All rigid plastics retain heat well. For example, fiberglass retains heat 4.4 x more efficiently than glass and 70.8 x more efficient than polyethylene film. Plastic panels have fewer lap joints through which heat can escape. Corrugation in some types makes a very tight fit at lap joints, thus saving heat. The total amount of light transmitted through fiberglass rigid panels is roughly equal to that transmitted through glass. Fiberglass actually has the advantage over glass because it transmits less heat. During the summer a fiberglass covered greenhouse requires less cooling than a glass greenhouse of the same size. Fiberglass with PVC is a durable, relatively lightweight material that resists damage from weather, ultraviolet radiation, and acid rain. Recent improvements in plastics include the introduction of structured sheets. Available in both acrylic and poly carbonate, these are double skinned (for insulation) or corrugated. Acrylic transmits light better but polycarbonate is stronger and more resistant to impact and fire. Both materials can be used on curved areas. When purchasing polycarbonate panels make sure they are UV coated to guard against premature yellowing.

To Build or Buy a Kit?

Once you have chosen the style of greenhouse you want, you must decide whether to build your own from a plan or assemble a prefabricated model from a kit. Base your decision on such factors as your available time, budget, and building skills. If you want to construct your own but are inexperienced, consider hiring a carpenter to help you. If saving money is your goal, you may be able to do that by building your own, especially if you are able to use scrap materials such as old windows and doors. Even if you buy new materials, you can build a greenhouse for less money than prefab kits. On the other hand if money is not an issue but your skills are then a kit is a logical choice. Kits provide everything you need, including a lightweight foundation for some models. Before deciding on a kit, send away for catalogs if available. A greenhouse company with an informative web-site can provide more information than a brochure and you will always have a fresh copy on your computer. Make sure assembly instructions are included as well as a list of any materials you may have to buy to outfit the greenhouse such as landscaping cloth, gravel, patio blocks etc. A nice thing about Google ads is that they provide additional info on greenhouse kits and greenhouse plans as well as Lexan polycarbonate greenhouse coverings

• Compare Kits (wood & metal frame)

• Lexan Corrugated Specs

• Lexan Thermoclear Specs

• Greenhouse Videos