I get this question a lot. What is the difference between a glass greenhouse and a polycarbonate greenhouse. I am going to assume that the frames are basically the same, so the biggest difference will be in the glazing material.
Glass greenhouses will be more expensive than a polycarbonate greenhouse. Especially with a curved eave. The glass is all tempered (safety) glass, even the curve. The curved tempered glass is more expensive than doing a curved polycarbonate. The twinwall polycarbonate is flexible enough that it is bent right onsite as you are installing the kit. There are no special tools or processes needed to do this. You just simply bend it over into the curved frame and attach it.
Looks are another obvious difference. The glass greenhouse will have more of a timeless look to it. I suppose if you want to use the word “fancier” that could even be applied. Just in looks, not in function. A lot of people don’t like the polycarbonate glazed greenhouse as it will be translucent rather than transparent. It will not be like looking through a window like the glass greenhouse will. Twinwall polycarbonate is made up of 2 sheets, an interior and an exterior. These sheets are both clear and would look much like looking through a window if you peeled the walls apart. Multiwall polycarbonate is much like looking down the end of a cardboard box. You will have the exterior and the interior sheet with a rib in between them. The rib will run straight between the 2 sheets, not curvy like in a cardboard box. This rib is what distorts your view. You can see color in a polycarbonate greenhouse, just not a clear form.
The glass greenhouse will not be as well insulated as the polycarbonate greenhouse. A single glass greenhouse will have an R value of approximately 0.95. A 6mm twinwall polycarbonate greenhouse will have an R value of around 1.6. This means that if you have the same size single glass greenhouse and polycarbonate greenhouse in the same location, trying to heat it to the same temperature, the glass greenhouse will cost you more to heat. It seems from the difference in the R value that it would be about twice as much. That is not the case. There is a formula that uses the size of the greenhouse, the difference in the temperature inside and outside the greenhouse, and the glazing material. If this is a consideration in your instance, the best way to determine how many BTU’s you will need is to actually do the calculations.
Breakage is another issue. Tempered glass will break if it is hit in the right manner. There is just no way around it. But, it is tougher than regular float glass, and it will shatter into small pieces, so safety is not a concern. Polycarbonate has a 10 year warranty against hail damage. It is a very tough material. It will not break like the glass.
Lifetime of the glazing material is the last issue I will discuss. Glass will pretty much last forever unless it is broken. Polycarbonate generally has a warranty that the light transmission will not vary more than a specified number in 10 years. This is just a fancy way of saying that it will not turn yellow or get brittle. Some of the manufacturers have extended their warranties to 15 and even 20 years. I have personally seen sheets that were 15 years old and still in use. They looked just fine. I have had reports back of 20 year lifetime on the material.
Glass greenhouses vs polycarbonate greenhouses? What is the conclusion. They both have their benefits, it just depends on which fits best into your needs. The best decision is to make sure to get a greenhouse, no matter what type. It will give you hours of enjoyment, produce food for your family, protect your orchids, and be the envy of your friends and neighbors.