Greenhouse Planning: Quick look at the PROS & CONS of Glass vs. Polycarbonate

My first greenhouse was made with a mishmash of recycled windows and with corrugated polycarbonate SUNTUF for the roof and some of the sides.

SUNTUF was light and surprisingly easy to work with, though took weeks to special order in the parts that joined it together. It even looked pretty nice when it was all finished. But it didn't wear well in my location, at least in appearance, because after a year it was basically covered in green dirt. Perhaps its an issue only is Northwest areas, but with our cool but very wet winters, the time when moss grows on everything, including bus stop shelters, the poly carb became coating in what was probably moss spores or other things brought by the wind. Come spring, scrub as we may, that stuff would NOT come off.

So although in articles and youtube videos you can find a lot of polycarbonate greenhouses, you can see why I'm a little wary. Although ease and functionality matter more than beauty, can we all admit that at least a small part of us would love to have a greenhouse that also looks good for the most part?

So, full disclosure, that's my mind set coming into this topic. However, I'm trying to keep an open mind so let's check out some pros and cons to different materials, mainly variations of polycarbonate vs. glass.

Corrugated Polycarbonate:

Corrugated polycarbonate offers high light transmission, is light and clear and pretty tough. There's no worry about safety with these, unless you try to step on them (not a good idea!) Once you have all the parts, they go up very easily.

R rating: 0.84 U value: 1.2 (heat loss)

Pros:
Very cost effective.
Very light to work with.
90% UV transmission.
Pliable.
Easy to order from Hardware stores, for the most part.

Cons:
Breakable.
Not a great R rating for many places, often only suitable for 3 season greenhouse.
Starts changing colour without a year (at least in the Pacific Northwest).
Aesthetically ok, not great. Let's say 6/10.
Made from fossil fuels. Maybe not be recyclable in your area, but may be recyclable if you have good facilities which recycle plastic. Check your local listings or in BC myrecyclopedia.ca.

Final notes:
I think if I was building a lighter greenhouse I would use corrugated, keeping in mind it won't look nice for long.

Polycarbonate (double walled or better)

Polycarbonate is an increasingly popular option for hobbyists as it is lighter to work with than glass and often more durable, with less safety concerns. It's main downside is aesthetic.

R rating: single is 0.83 but double is 1.42. Many people use bubble wrap in the winter.

Pros:
Much better R rating than above corrugated poly and below single paned glass.
Light
Tough
Won't shatter if a football hits it.
Less safety concern compared to glass.
Some argue that non-clear panels reduce the problem of birds flying into your greenhouse.

Cons:
Aesthetics: Doesn't look as nice as other options, you can't see in clearly or out. But maybe for some people that's a plus. IMO, let's say 4/10.
Appearance also changes over time, though I don't have personal experience with it.
Made from fossil fuels. Maybe not be recyclable in your area, but may be recyclable if you have good facilities which recycle plastic. Check your local listings or in BC myrecyclopedia.ca.
Wears out faster than glass, is easier to scratch and outgasses toxins.

Glass

Most people, when they imagine creating an orchid greenhouse, probably imagine a glass greenhouse first, before they research glass and then balk at the price associated. Grand conservatories and glass greenhouses are the things of luxurious manors.

R rating: 0.91 to 2.38depending on single or double pane and the amount of space between the panes. U value: 1.1 - 0.7 for double. (Lower is better.)

Glass looks lovely and if you live in an area that gets cold in the winter but you can afford double walled glass then you're all set.

Pros:
Beautiful.
Clear.
Can have a good R rating.
You can mix and match and customize your greenhouse, you can source some windows from garage sales and antique stores and have something unique if you're the pinterest kind of person.
You can source greenhouse glass also from used sites such as usedvictoria, kijiji and craigslist.

Ecologically neutral. Glass is not made with fossil fuels, and even in a landfill it is, arguably, ecologically neutral (just sand). Glass is also recyclable. Glass with metal frames can be recycled in many places as "metal". Check your local listings or in BC myrecyclopedia.ca .

Cons:
Heavy. You need to make sure your frame is well built.
Can shatter or break and can be annoying to replace, can cause a safety concern. You need to use safety glass if overhead or within a foot of a door. You can cut yourself while installing it.
You may need to apply coatings during high sun to shade your plants, which may require removal at times and maintenance, which some might find annoying. Because glass is clear it can create hotspots.
It's clear, so there's less privacy (if that's something you are craving.) Except for after 20 or 50 years sometimes seals can break so that the glass slowly starts to become foggy.
Can create condensation in the winter which results in dripping in your greenhouse.

Not sure which one you're going to do? Here's another idea:

Some Glass, some Polycarbonate.

Sometimes you find yourself thinking "Well I really love the look of glass. Though I don't know if I want to deal with the hassle associated with having a glass roof and the special kinds of glass I'll need for that, given that I want to do it mostly myself..."
In that case you might find yourself considering some poly and some glass. Polycarbonate roof for lightness and safety, Glass walls for look and clarity.

Here's two cool examples of that:

Here's an interesting link to someone who has done that. https://www.orchidsforum.com/threads/alexey-cool-to-warm-all-in-one-greenhouse.14454/ and on Vancouver Island.

And another example of a cool mixed media greenhouse http://www.njpen.com/neighbors-raise-greenhouse-in-collingswood-community-garden/#prettyPhoto (Photos by Tricia Burrough.)

If you have any experience with poly roof and glass sides greenhouse, please contact me as I'd love to hear how it went.

More Greenhouse articles coming soon including wood vs. metal frame and greenhouse architecture. If you have a topic you'd like to read about, don't hesitate to contact me.

Resources:

http://www.advancegreenhouses.com/planning-and-building-a-greenhouse/

American Orchid Society very comprehensive article on building a greenhouse. (PDF)

References:

http://www.homemadehints.com/greenhouse-covering-materials-comparison/
http://www.telegraph.co.uk/gardening/gardeningequipment/6537880/Greenhouses-why-polycarbonate-beats-glass.html
http://bwgreenhouse.ca/R-valueU-value.html