As a greenhouse gardener, one of the most important decisions you will make in buying a greenhouse kit or building one from scratch is whether to use glass or polycarbonate material. The whole point of a greenhouse is to let in light and trap the heat to keep plants warm and growing. You want a material that does this well and that will last for a long time. Traditionally, greenhouses have used glass panels. In recent years, there have been advancements made in twin-wall polycarbonate that make it equal to or even better than glass in many ways. This makes the decision tougher than it used to be. Let’s consider a few characteristics of each.
Glass is clear so it lets in a lot more direct light. Polycarbonate plastic distorts the light that it lets in, which is called diffuse light. Plants actually do better with diffuse light since direct light can scorch or overheat them. Diffuse light is able to reach all around the plants so that they are lit evenly instead of the majority of light going to the top portion. In this situation, plants tend to grow faster. The clear advantage here goes to polycarbonate.
The whole point of a greenhouse is to use the power of the sun to heat a room for growing out of season. If the room does not retain heat then it is useless. Glass is both quick to heat up and quick to cool down, so it does not retain heat for long. A single sheet of polycarbonate film is actually less able to retain heat than standard greenhouse glass. Fortunately, most polycarbonate products for greenhouses are actually made of a double wall construction, where two sheets of film are put together with space in between. This internal buffer space makes double wall polycarbonate material a much better heat retainer than glass.
Both glass and traditional polycarbonate are actually outperformed by Solexx though. It has more than twice the heat retention of standard glass and is readily available for purchase here at greenhouseemporium.com, so if heat retention is a major concern then look no further. We also offer several kits featuring the Solexx covering.
Glass is breakable, of course, but polycarbonate sheet plastic is also at risk of scratching and tearing. Polycarbonate needs to be treated with UV protectant to prevent it from yellowing and breaking down. Glass does not need this extra treatment. If any portion of the cover needs to be patched or replaced, it is much easier to do so with individual glass panes instead of replacing an entire sheet of polycarbonate. Most long-term polycarbonates are made to last around ten years. Generally, the warranty length on the product is a good indication of how long you should expect it to hold up. Glass will last as long as it is not broken.
Most polycarbonates require little to no maintenance, but glass is a different story. For a classic clear look, you may have to clean it on a regular basis depending on use. Unless you have an expensive double-pane installation it will also sweat in colder weather. Since it lets in more direct light you might also need to have some sort of shading system and will need to be more diligent about venting and airflow in case it gets too hot in a glass greenhouse.
Neither material is overly easy or difficult to install. Polycarbonate and twin-walled polycarbonate can be installed in larger sections, but it needs to be handled properly to prevent damage to the sheet. Double-walled polycarbonate also needs to be sealed properly along any edge that has been cut or else moisture, mold, and bugs can get into the void between sheets. The difficulty with glass installation comes in the framing and finishing, but if you purchase a kit instead of trying to use reclaimed glass and windows, then the guesswork is removed from the equation.
The cost of glass and polycarbonate sheet for a greenhouse covering can vary based on source and quality of the material. The handy grower can save a good deal of money by building their own greenhouse from reclaimed glass panels, but as previously mentioned, this can be difficult and requires some skill. There are plenty of cheap polycarbonate options but these tend to not last very long nor perform well. Since the covering is the main provider of function for your greenhouse, we strongly recommend investing in a quality product that will last for many years. It may seem like a good idea to buy a cheap kit at first, but when you are replacing it every few years the cost and labor quickly adds up to more than if you had invested in a quality house, to begin with.
Greenhouse design is a very personal decision to make. Glass and polycarbonate have their own pros and cons. The majority of the analysis in this article is from the viewpoint of the novice grower, so you might not find certain aspects mentioned to actually be a con or positive for you. For example, if you have access to a good amount of quality unused glass then the argument of polycarbonate versus glass is pretty much moot. Both materials are good enough to make nice greenhouses so free or deeply discounted material of a decent quality is a major plus.
For the beginner grower, polycarbonate may be the better choice. It definitely performs the desired function of good lighting and heat retention better than glass. It may be a bit more expensive up front but will require less maintenance and allow you to focus more on your actual growing instead of greenhouse maintenance. If you do go with polycarbonate it is important to buy quality material. There is increasingly polycarbonate material on the market that is of inferior quality and non-virgin material. These products will not last more than a couple of years and you will end up spending more money having to constantly redo your greenhouse. This is the type of thing that you should invest in so you have many years of use. A beautiful option is the Riverstone Monticello Greenhouse. It'll last you years and years without wear and tear.