If you’re considering getting your first greenhouse or building one yourself, one of the biggest decisions you have to make is in regards to the type of glazing. Two of the most common greenhouse glazing materials are glass and polycarbonate. Both materials offer many benefits, but which is the best greenhouse material?
Traditional greenhouses were made with glass, but advancements in technology have resulted in many more options, including polycarbonate. While the crystal-clear appearance of glass is beautiful and allows for maximum light transmission, polycarbonate glazing offers better light diffusion and insulation. Ultimately, which glazing is best comes down to your personal preferences, local climate, and gardening needs.
Since one of the main reasons for getting a greenhouse is to enable you to extend the growing season, you want a glazing that will do just that while lasting for many years. To help you determine whether glass of polycarbonate is better for you, we’ve compiled the pros and cons of each type of glazing in this article.
Glass glazing for greenhouses
Many gardeners choose glass as their preferred greenhouse glazing because they love the look of a traditional glass greenhouse. In addition to its aesthetic appeal, glass offers the highest amount of light penetration. With so much direct light, plants grown in a glass greenhouse are sure to thrive. Or are they? Let’s take a closer look at the pros & cons of this glazing:
Pros – why glass is a good choice:
- Crystal-clear appearance: You can see through glass clearly, which enhances the appearance of a greenhouse and gives it that “traditional” look.
- High light transmission: Glass allows in the maximum amount of natural light for plants.
- No fading or discoloration: While other covering materials may fade or become opaque over time, glass retains its clarity for years to come. While it may fog up or accumulate debris, it’s easy to clean, thereby allowing it to maintain its appearance and ability to transmit light.
- Durable: Glass is a long-lasting material that doesn’t break down over time, though it may shatter if it gets hit directly.
- Flame-resistant: It’s safe to have a barbecue or fire pit near your glass greenhouse.
- Natural resource: Glass is a natural and renewable resource.
- Easily up-cycled: If you want to build your own greenhouse, you can salvage old windows or doors, usually at a steep discount.
- Easy to replace: You can order or purchase glass panes locally, making it easy to replace broken panels.
Cons – why glass might not be a good choice:
- No heat protection or diffusion: The clarity of glass is lovely, but it doesn’t provide protection from the sun. While this can be a great benefit in colder climates, it may be the death of your plants if you live in the desert, unless you install shade cloths inside or outside your greenhouse.
- Higher heating/cooling costs: Since glass doesn’t offer much insulation, you may have to supplement with heating or cooling to maintain a steady climate.
- Higher price for greenhouse kits: Ready-made glass greenhouses are not cheap, as the greenhouse frame has to be sturdy and the manufacturer has to take special precautions when it comes to shipping/delivery.
- Danger of breaking glass: Although high-quality greenhouse glass panels will not break easily, a fallen tree branch or errant pebble could result in broken glass. Although more expensive, you could consider tempered or safety glass, which doesn’t break into shards but rather lots of little pieces.
- Tricky to set-up: Glass greenhouses are not so easy to set up. You need a level surface (preferably a concrete slab) in order to prevent your glass cracking over time. This is important to keep in mind if you’re hoping to build your own greenhouse from scratch. Learn more about building greenhouse foundations here!
- Heavier material: Glass is cumbersome to transport and work with, especially when working with large panes.
- Minimum insulation: Single pane glass does not provide much insulation, and while double pane glass is better in this regard, it is also quite expensive.
- Maintenance: In order to maintain the beautiful and clear appearance of glass, you have to clean it frequently, particularly if you have hard water.
Polycarbonate glazing for greenhouses
Polycarbonate glazing is a premium choice for almost any type of greenhouse. It can withstand harsh weather conditions, it’s durable, and offers superior insulation. We discuss the pros and cons of polycarbonate in greater detail below:
Pros – why polycarbonate is a good choice:
- Sturdiness: Although polycarbonate has both rigid and flexible grades, the flexible plastic doesn’t easily crack under stress.
- Light diffusion: Polycarbonate glazing diffuses light, thereby resulting in more even light distribution to all plants. There are special polycarbonate panels (e.g. Solexx) that have extra light-diffusing features for optimum plant growth.
- UV protection: Because polycarbonate is not fully transparent, it protects plants from harsh UV exposure, which is particularly notable if you’re growing sensitive or young plants, or if you live in a particularly bright climate.
- Better insulation: Polycarbonate has the ability to retain heat better than glass. Multi-wall polycarbonate has air pockets in between that retain heat, resulting in a more stable inner climate.
- Lightweight: Polycarbonate is lightweight and easy to work with.
- Durability: Polycarbonate greenhouses are durable and weather resistant, able to withstand even extreme weather conditions such as heavy snow or rain.
- Low maintenance: Since a crystal-clear appearance isn’t necessary, you only need to clean a polycarbonate greenhouse once or twice a year.
- Flame-resistant: It is safe to have a barbecue or fire pit near your glass greenhouse.
Cons – why Polycarbonate might not be a good choice:
- Appearance: You cannot see right through polycarbonate, so it doesn’t give you the classic greenhouse look.
- Prone to scratching: It’s not advisable to use chemical solutions or scrubs to clean polycarbonate glazing, as it scratches easily and can’t be polished. Prevent scratches by using gentle cleaning solutions and clean cloths.
- Condensation: Multi-wall polycarbonate can accumulate moisture between the layers, which could result in algae. While it’s difficult to get rid of condensation in the layers, you can prevent it by tightly installing the panels and adding caulking to seal the gaps.
- Dust accumulation: If not installed properly, polycarbonate panels may accumulate dust over time. You can’t clean dust between the layers, and it may affect light transmission over time. Therefore, it’s best to prevent this by ensuring a snug and sealed fit.
- Not a natural resource: Polycarbonates are a group of thermoplastic polymers that are chemically produced. Like other plastics, they are difficult to recycle and can’t be easily up-cycled.
- Hard to replace: While the initial cost of polycarbonate greenhouse kits is less than that of glass greenhouse kits, it can be costly and difficult to replace broken or damaged panels. You typically have to contact the manufacturer of your greenhouse directly for replacement panels.
Now, let’s compare the key features of the two glazing materials
Here, we’ll compare the key features of both types of glazing to help you make your final decision.
Light distribution
Glass is clear so it lets in a lot more direct light, while polycarbonate diffuses the light that it lets in. Notably, research shows that plants actually use diffuse light “more efficiently than direct light.” That’s because diffuse light is able to penetrate deeper into the plant canopy, leading to increased photosynthesis and thus faster growth.
Plus, direct light can scorch sensitive plants, including seedlings, whereas diffuse light tends to be more gentle.
Insulation and heat retention
Hobby greenhouses are so popular because they allow gardeners to extend the growing season, or even grow year-round. However, if the glazing material doesn’t retain heat, then a greenhouse is as good as useless. While glass retains some heat, it doesn’t do so for long. That makes glass a poor choice if you’re hoping to grow during the colder months.
On the other hand, most polycarbonate greenhouse glazing products are made of twin wall material, where two sheets of film are put together with space in between. This internal buffer makes twin wall Polycarbonate much better at insulating than glass.
However, both glass and traditional polycarbonate are outperformed by Solexx, which has superior heat retention and is readily available for purchase here at Greenhouse Emporium. So, if heat retention is a major concern then look no further; we offer several kits featuring the Solexx covering.
If Solexx is not the style you are looking for, check out Riga greenhouses; they make perfect winter greenhouses.
Durability
Glass is breakable, of course, but polycarbonate panels are at risk of scratching and tearing. Also, polycarbonate should be treated with UV protectant to prevent it from yellowing and breaking down over time. Nowadays, most store-bought panels already have this, but you may need to reapply the coating after several years of use.
Glass panels don’t need any kind of UV protection. Therefore, they could last forever – as long as they aren’t broken. Most polycarbonate panels, on the other hand, are made to last no more than ten years. Generally, the product’s warranty period is a good indication of how long you should expect it to hold up.
In terms of replacing individual panels in the case of breakage, it’s easier to do so with glass panes than with polycarbonate panels, as glass tends to be locally available whereas polycarbonate has to be sourced from the manufacturer. If you buy a greenhouse kit, check to see if the manufacturer readily offers replacement parts.
Maintenance
Most polycarbonate panels require little maintenance, whereas glass may need to be cleaned on a regular basis to maintain its appearance.
Also, glass panels tend to “sweat” in colder weather. And since they let in more direct light, you might need to have some sort of shading system and will need to be more diligent about airflow in case it gets too hot.
Installation
Neither material is overly easy or difficult to install. Polycarbonate can be installed in larger sections, but it needs to be handled properly to prevent damage to the sheet (especially the edges and corners). It 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.
Glass is more fragile than polycarbonate and it is most certainly heavier. Handling larger glass panes may therefore be more difficult.
Cost
The cost of glass and polycarbonate sheets for a greenhouse can vary based on the source and quality of the material. The resourceful builder 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 on the market, but these tend to not last very long nor perform well. Since the covering is the main provider of heat and light transmission for your greenhouse, we strongly recommend investing in a quality product that will last for many years. In fact, while it may seem like a good idea to buy a cheap kit at first, you’ll likely have to replace it after just a few years of use, which may add up to more than if you had invested in a quality greenhouse to begin with.
Glass vs Polycarbonate – Which is the best option?
Greenhouse design is a personal journey, and ultimately, whether you go with glass or polycarbonate glazing is up to you. Hopefully, you’re able to use the pros and cons discussed in this article to make an informed decision that works best for your needs.
For example, if you have access to cheap, quality glass, then the argument of polycarbonate vs. glass may very well be moot. Both materials are good enough to make a nice greenhouse with, so free or deeply discounted material of decent quality is a major plus.
For the beginner grower, polycarbonate may be the better choice. It results in good lighting and heat retention, and tends to be less expensive upfront (especially if you’re buying a kit).
If you decide to go with polycarbonate, it’s important to buy quality material that will last for more than a few years so you’re not having to redo your greenhouse every few years. In fact, high-quality glazing is the type of thing that you should invest in so you have many years of use.
At Greenhouse Emporium, we offer plenty of long-lasting greenhouse kits. Here are some brands worth looking at:
Ultimately, it all comes down to your personal preferences. If the appearance of your greenhouse means a lot to you, glass glazing might be the better option for you. If you’re more particular about creating a favorable environment for your fruits and vegetables, polycarbonate is the way to go. The choice is yours to make!
20 comments
where would I find a Monticello greenhouse and what would the price be for a 8×10
Hi Sandy, the available sizes are 8×8 and 8×12, not 8×10. Here is the Monticello 8×12 Base Kit. You can also use the menu to navigate to them – Greenhouses > under Brands click “Monticello”.
Hi, i was thinking of purchasing a polycarbonate greenhouse to grow organic vegetables in, but I am uncertain if the polycarbonate will be harmful to my vegetable crops by way of chemical contamination – i fear that harmful chemicals may be released into the air and leached into my garden beds from the polycarbonate walls. I would appreciate you views on this matter. Thank you
Hi Kathrine, there isn’t enough evidence to prove that polycarbonate pollutes the air. Also, it will likely depend on how it is manufactured. So, I cannot give you any view on it. What I can say is: if you are concerned, go for a glass greenhouse. This way you don’t have to worry about potential pollutants from the glazing.
I plan to use my glasshouse for tomatoes only. I live in Dunedin 200 m above sea level where in summer we have average temp of about 18-19 – with good days 22-24 and cool days 13-14 C. l wonder if polycarbonate might be the better choice – but realise glass will give hotter temps on hot days. What would you suggest: glass v polycarbonate in my environment?
Hi Wayne, it’s not only about the material. The greenhouse should also be more insulated if you only get temperatures like this. Glass doesn’t provide as much insulation compared to high-quality Polycarbonate and Polycarbonate can have light-diffusing properties. However, if you already have a glass greenhouse, I’d work with that and add accessories to keep the temp at a good level. Tomatoes need plenty of sun and heat to develop the delicious taste. And it should be warm enough in your area because it’s always a bit warmer inside the greenhouse, especially if you fill it with a lot of plants.
You mention adding accessories to keep temp at a good level. What accessories are you meaning?
For winter: Heating
For hotter days: shade cloths, ventilation, maybe even a misting or evaporative cooling system depending on how hot it gets inside.
I am not sure I have a recommendation from you yet -if I am to buy one product – glass or polycarbonate – which would you buy? Remember I am looking to mostly grow tomatoes in Dunedin where average summer temps are lower than further north.
Sorry, Wayne! I thought you meant that you already had a glass greenhouse. Now, I would suggest a high-quality Polycarbonate greenhouse that has great insulation. This way you can keep a steadier temperature inside. Polycarbonate still lets the sunshine through but it breaks it a bit (diffusion). You may want to think about grow lights for the wintertime (unless you want to take a break during this time).
My son in law’s family owns a special order glass company. When he found out that I want to build a greenhouse, he asked if I wanted some 1 inch thick 2 x 8 sandblasted glass panels to use on the greenhouse. The customer that ordered them decided on a different size. The glass would be free. Would these work OK for a greenhouse? Would they let enough light through? My biggest concern is if there is a way to safely install them on the roof. They are quite heavy.
Sorry, Ronda. I can’t answer this because we have no experience with such thick glass panels. I’d be really concerned about the weight because the whole structure has to hold all panels. I am not a structural engineer nor do I know what you plan to use for framing. However, even these thick panels should let enough light through. Sorry that I can’t be of much help. Please, share your experience with us when you made your decision or build the greenhouse so we can learn from it, too. We are always interested to hear about projects!
This has been so Informative, we are building a large greenhouse, after reading your information I think we are going to go Polycarbonate Thank you so much once its all built we will follow with a pic and a review.
Thanks, Hazel! Glad we were able to help you. We are looking forward to hearing about your project.
Unfortunately we got the structure built but rest had to be on hold. Now ready to get it finished can I ask what thickness of twin wall polycarbonate should we go for. Based in Scotland Thanks
Hazel, our blog How Thick Should Polycarbonate Be for a Greenhouse may be helpful to you as you continue with your greenhouse. In general, 8mm thickness and higher is good for all weather. You will also want to seal the greenhouse well. This will help with maintaining the desired temperatures year round.
Hello
I trying to decide between glass and polycarbonate for a small greenhouse for tomatoes etc in the summer but mainly overwintering plants and salad leaves. I hadn’t really considered Polycarbonate before but it sounds like a good option, my main concern is for the environment. Can the sheets be recycled or manufactured from recycled materials?
Hi Helen! Yes, Polycarbonate can be recycled (they make other products out of it). I haven’t seen any Polycarbonate manufactured from recycled materials, though.
Hello Greenhouse Emporium,
What should the thickness be of a single polycarbonate tile 61 x61 cm for a greenhouse?
Hello KJ!
This is a highly individual question and depends on your own needs.
As a rule of thumb, 8 mm and higher will do fine for greenhouse coverage, for any type of weather. If you don’t get many icy-cold nights or if you plan on heating your greenhouse throughout the cold season, you might be good with thinner panels.
4 mm thick panels are primarily used as a “season extender” not necessarily for year round growing.
Then again, you are going to find manufacturers, such as Solexx, that have a better insulation factor than 8 mm twin walls while having 3.5 or 5 mm walls. This is when R-values come in handy. This is because it depends on the material and the greenhouse structure.