One of the most important features of a greenhouse is the glazing, or covering, used as it needs to let in plenty of light while insulating the plants and providing durability. Fiberglass is a popular material used for glazing greenhouses, and its pros include providing good diffused light and good insulation. It is also easy to work with, and fairly inexpensive. The problems with a fiberglass greenhouse are that it may yellow, is highly combustible, is hard to clean if corrugated and can expose dangerous glass fibers when cut.
Different types and grades of material can be used to build a fiberglass greenhouse. Some grades will last for 20 years, while others will last for only three. Corrugated fiberglass is considered very durable and its strength is beneficial for greenhouses located in climates with high winds or heavy snows. The downside of corrugated fiberglass is that it can be hard to clean, and the dirtier it gets, the less light it lets into the greenhouse. In general, fiberglass tends to not expand or contract in changing temperatures as much as other materials.
Compared to glass, a fiberglass greenhouse lets in almost as much light but tends to insulate much better. Insulation is very important in the cold winter months when plants need to be kept warm. The light that comes through a fiberglass greenhouse is also diffused, which helps the photosynthesis process that plants go through to grow. A fiberglass greenhouse will usually have an ultraviolet gel protective coating which will protect the fiberglass from yellowing right away. This coating will burn off over time, however, and the yellowed fiberglass greenhouse can be less effective at letting in light and may be considered unattractive.
Building a fiberglass greenhouse is usually much simpler than a greenhouse made out of glass because fiberglass is much lighter and easier to transport. Expanding an existing fiberglass greenhouse is also a simpler task because fiberglass is easy to cut and is fairly flexible. If cost is a concern, fiberglass is considered to be one of the least expensive greenhouse glazing options.
Extreme caution should always be taken when cutting fiberglass, however, because the tiny glass fibers can be inhaled and irritate the lungs as well as exposed skin. Gloves, long sleeves, and breathing masks should always be worn when cutting fiberglass or cleaning an area where it has been cut. Heat sources should never be placed near fiberglass because it is extremely flammable, which can be a problem if the greenhouse will need to be heated internally during the winter.