“Plastic” and “durability” aren’t usually words that should go together, but in the case of greenhouses they can.
Long-lasting polycarbonate is worth considering as the covering material for your greenhouse, especially when compared to the traditional use of glass.
In the case of modern tempered glass, rocks and hail shatter the panes with little effort. Alternatively, polycarbonate sheets are known to withstand the strike of a hammer. It has been mentioned by some that an advantage to glass is the visibility of plants from the outside, however current advancements in technology have resulted in the polycarbonate sheets maintaining better clarity than glass.
Glass is also less desirable when insulation is considered. Polycarbonate is close to twice as effective at insulation than glass. Looking at the greenhouse as a holistic system, the increased energy savings from effective insulation may make polycarbonate greenhouses more eco-friendly than a glass one.
Light is also diffused differently with the two materials. Polycarbonate covering diffuses the light coming in, causing light to reach areas of the greenhouse that it wouldn’t with glass. U.K. gardening expert Bunny Guinness also points out that polycarbonate protects naked gardeners from almost all UV rays that are dangerous.
Polycarbonate has only come into general use for greenhouses in the last 40 years; much experimentation is still taking place. You can research the latest options on your own and order your materials from a big box hardware store, or online.
My personal recommendation would be to seek out an expert.
Polycarbonate greenhouse specialists have a wider variety of choices than the big box stores, and usually compare very well on price. Specialists will also carry accessories designed for building with polycarbonate, and many answer questions in person or over the phone.
We’re lucky to have one such specialist near Insteading HQ—Charley’s Greenhouses. They’ve been building and innovating greenhouses for four decades now, both for Seattle-area folks and on a national level through their website.
If you want to learn more about building greenhouses, not just polycarbonate ones, I highly recommend their YouTube series on the topic.