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What are the Pros and Cons of a Fiberglass Greenhouse?

By Kaitlyn N. Watkins
Updated May 16, 2024
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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.

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Discussion Comments

By SexyGardener — On May 15, 2014

I did tons of research and I looked at practically every, single backyard greenhouse option under the sun (no pun intended), and I concluded that a one-piece, molded fiberglass greenhouse (thus, no assembly) is the way to go - diffused interior light, better heat retention in the winter, more rugged, and greater longevity. Who wants to put a greenhouse together from scratch if they don't have to?

Here's the rub: unless the fiberglass greenhouse comes with some kind of UV gel coating on the exterior (like a boat, or RV does) then the fiberglass will rapidly deteriorate, become a magnet for dirt and debris, and will discolor in no time. In my research, I found just two manufacturers of backyard fiberglass greenhouses that come with a gel coat on the exterior. One is overseas (making it too expensive to import, darn it), but the other is here in America. Hooray! They're called Solar Gem Greenhouses and they make them in Washington State, but I think they sell them across North America. I ended up buying one (a fifteen footer) and I have been thrilled. I live in a cold climate but I can garden year-round in mine. No regrets whatsoever. Hope that helps.

By browncoat — On Aug 21, 2013

@Fa5t3r - It's still a pretty good material for a greenhouse, particularly if the greenhouse frame is sturdy and can be used as permanent and the fiberglass is treated with care and replaced every decade or so.

Unfortunately, being cheap, it does eventually wear out and it can grow yellow and worn after a while. But, in my experience, other forms of glazing will also have these kinds of long term problems and tend to be more expensive to replace. So you might as well get the cheaper material, particularly as it works just as well as the more expensive stuff.

Do be careful about cutting it yourself though. The article author is right to point out that it can be very dangerous to inhale those fibers.

By Fa5t3r — On Aug 20, 2013

@Iluviaporos - I think the problem comes when people use artificial lighting and heating in their greenhouses. Usually that's not an issue with greenhouse kits because they are so small that they don't tend to have any need for electric additions.

But a larger greenhouse might also be made from fiberglass and if people aren't careful they could start a fire with what seems like an innocent light or heater.

By lluviaporos — On Aug 20, 2013

I had no idea that fiberglass would burn so easily. It kind of worries me, because I bought a cheap greenhouse kit for my aunt a few years ago, since I knew that she wanted to try growing her own sprouts and didn't really have room in the kitchen.

She loves it and grows a lot of little seedlings for various uses as well as a couple of small fruit trees in there. But I'll have to warn her that it might be a fire risk. I suppose if the air is somewhat humid then it might mitigate the risk.

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