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Glass vs Polycarbonate Greenhouse – Which Glazing is Better?

Woman in a greenhouse holding a plant with the text: Glass vs Polycarbonate Greenhouse

Table of Contents

If you are considering getting a greenhouse or building one yourself, you must have done your research and come up with this question: Do I get glass or do I just go for Polycarbonate glazing instead?

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 examine the pros and cons of both greenhouses.  

Now, the main reason for a greenhouse is to enable you to extend your growing season and create the perfect condition for your plants all year round. Therefore, you want to select a greenhouse glazing that’ll do just that perfectly while also lasting for many many years.

We are going to examine both greenhouse glazings critically. This will hopefully help you determine whether glass or Polycarbonate is better for you. 

Glass glazing for greenhouses 

Glass is a classic and beautiful glazing option. Many gardeners select glass greenhouses as their perfect choice due to its aesthetic appeal. It has been the traditional greenhouse building glazing material. It permits the highest amount of light penetration. Let’s briefly examine the pros & cons of this glazing.

Pros – why glass is a good choice:

  • Better looks: You can see through glass clearly. This enhances the appearance of a greenhouse and gives it the “traditional look.”
  • The maximum amount of natural light for plants: It has the highest light transmission. 
  • No fading or discoloration: While other covering materials tend to fade and become opaque, glass does not. It may fog up but that’s all. Glass will, therefore, transmit the same amount of light throughout its life. 
  • Long-lasting if breaking is prevented
  • Flame-resistant: So it’s completely okay to use it in garden areas where barbecues take place.
  • Natural resource: There are no chemicals used in the production.
  • Potentially cheap acquisition: You can potentially salvage old windows and build a greenhouse with it.
  • Easy to replace: You can order or purchase glass panes easily in your city. So, you can fix broken pieces faster.

Cons – why glass might not be a good choice:

  • No heat protection or diffusion: The clarity of the material is nice but it doesn’t break sun rays or provide protection from the sun. If you are in the desert or another sunny place, this might be the death of your plants. Shade cloths will become indispensable.
  • Higher heating/cooling costs: Regarding the previous point, you’ll also have to spend more to heat or cool a glass greenhouse. 
  • Higher price for greenhouse kits: Ready-made glass greenhouses can be quite pricey.
  • Danger of breaking glass: Glass can be a very fragile material and breaking of glass panels on the greenhouse can be very dangerous. However, tempered glass can reduce the danger and ensure safety.
  • Set-up: Glass greenhouses are not so easy to set up. In fact, the surface you are using for it must be completely plumb and level in order to prevent cracking of the glass over time. This may make it difficult for the do-it-yourself greenhouse builder.
  • Heavier material: Glass is quite heavy and cumbersome to work with, especially when working with large panes.
  • Not much insulation: Generally, glass does not provide as much insulation for your plant (unless the double-walled glass which is quite expensive). 
  • More maintenance: You have to clean the glass more frequently if you want to keep the beautiful appearance. This increases further if you are using hard water for irrigation. You may have to clean them once a month or every 2 weeks, depending on how clear you want them to be.
Glass greenhouse on top and Polycarbonate greenhouse at the bottom with the text: Glass or Polycarbonate - What glazing is better for your greenhouse

Polycarbonate glazing for greenhouses

Polycarbonate glazing is a premium choice for growers living in all kinds of climates. It can withstand harsh weather. It is long-lasting and can remain in good shape even after several hits from a ball. Polycarbonate greenhouses have excellent features but we’ll discuss the pros and cons of this greenhouse below.

Pros – why Polycarbonate is a good choice:

  • Sturdiness: Although Polycarbonate has both rigid and flexible grades, the flexible plastic doesn’t crack under stress easily. This makes them unbreakable and able to withstand massive force.
  • Protection from the sun: Polycarbonate breaks UV rays while letting in warmth and sunlight. It is a perfect plastic for greenhouses as it has a light transmission of 88%.
  • More light diffusion: Compared to glass, it lets in diffused light that benefits plants. For example, the twin-wall Polycarbonate has a cellular structure that breaks sunlight. There are special Polycarbonate panels (e.g. Solexx) that have extra light-diffusing features for optimum plant growth.
  • More insulation: Polycarbonate has the ability to retain heat better than glass. The twin-wall design has a double glazing effect with air pockets in between that decrease heat loss. Ideally, an 8 mm Polycarbonate thickness for greenhouse sides and 10 mm thick plastic for the roof would be perfect. 
  • Lightweight: This makes it incredibly easy to work with. It is also easy to move around without worrying that it might break. 
  • Durability: Polycarbonate greenhouses are durable and weather resistant. They withstand harsh environments, including snow, rain, and burning sun. 
  • Low maintenance: Doesn’t need regular cleaning like glass – once or twice a year will be fine. 
  • Flame-resistant: So it’s completely okay to use it in garden areas where barbecues take place.

Cons – why Polycarbonate is not so good:

  • Doesn’t look as nice: This is the major disadvantage. You cannot see 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 up Polycarbonate greenhouses. Scratches are not easy to repair or get rid of. It cannot be polished. As long as you prevent them, your Polycarbonate will be in good shape.
  • Condensation: Twin-wall polycarbonate can accumulate moisture between the layers. This may accelerate the level of algae development. This doesn’t have to happen if the greenhouse is installed properly (tightly put together).
  • Dust accumulation: If not installed properly, panels may easily accumulate dust over a long time. Cleaning will be difficult and in addition, the dust would build up and affect light transmission. You can easily deal with this by ensuring that your panels fit snugly into the frame profiles so that there is no entry for dust.
  • Non-natural resource: Polycarbonates are a group of thermoplastic polymers. They are chemically produced.
  • Higher costs & harder to replace: While Polycarbonate greenhouse kits are cheaper than glass greenhouse kits, Polycarbonate may still be more expensive than salvaged glass. Buying it also is not as straight-forward as with glass. Replacing a broken panel may take more time because you have to contact the manufacturer and wait for them to send it out.

Now, let’s compare the key features of the two glazing materials

Here, we’ll compare the crucial features of both greenhouses. This would help you to make a decision. 

Light distribution

Glass is clear so it lets in a lot more direct light. Polycarbonate distorts the light that it lets in, which is called light diffusion. Plants actually do better with diffused light, since direct light can scorch or overheat them. 

Diffused light is able to reach all around the plants so that they are lit evenly instead of the majority of light going to the surface or top. So, plants tend to grow faster with diffused light. 

As mentioned above, Polycarbonate also filters UV rays. This is also beneficial to your plants.

Insulation and heat retention

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. This can be lethal for plants in the long winter nights.

However, a single sheet of Polycarbonate film is actually less able to retain heat than standard glass. Fortunately, most Polycarbonate products for greenhouses are actually made of double-walled material, where two sheets of film are put together with space in between. This internal buffer space makes twin-wall Polycarbonate a much better heat retainer and insulator 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 Greenhouse Emporium. So, if heat retention is a major concern then look no further. We also offer several kits featuring the Solexx covering

If Solexx is not the style you are looking for, you should check out Riga greenhouses. They are the perfect deep winter greenhouses.

Durability

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. Nowadays, store-bought panels already have this. There is no need for an extra layer.

Glass does not have this problem at all. Therefore, it is durable glazing that could last forever – as long as it is not broken. Most 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.

If any portion of the cover needs to be patched or replaced, it is much easier to do so with individual glass panes. You can purchase new pieces easily in your local area. Replacing an entire sheet of Polycarbonate may not be as easy and quick because you have to order it from the manufacturer. 

Maintenance

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.

Installed Polycarbonate Greenhouse
Polycarbonate greenhouse

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 edges). 

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 a bit more fragile than Polycarbonate and it is most certainly heavier. Handling larger glass panes may be difficult for some people because of the size and weight.

Cost

The cost of glass and Polycarbonate sheets for a greenhouse covering can vary based on the 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 greenhouse, to begin with.

Hand pulling money bills out of a black wallet
Money Money

Glass vs Polycarbonate – Which one is better?

Greenhouse design is a very personal decision to make. I’ve mentioned the pros and cons of glass and Polycarbonate. The majority of the analysis in this article is from the viewpoint of the novice grower. So, you might not find certain aspects actually to be a con or even 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 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 upfront but will require less maintenance and allow you to focus more on your actual growth instead of greenhouse maintenance. 

If you do go with Polycarbonate it is important to buy quality material. There is Polycarbonate material on the market that is of inferior quality. 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. 

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. We mentioned Solexx before but we also have more brands that are worth looking at:

Generally, it all goes down to your likes and dislikes. If the appearance of your greenhouse means a lot to you, a glass glazing would 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!

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Above is a glass greenhouse with plants inside. Below is a Polycarbonate greenhouse surrounded with plants. The text in the middle says Glass vs Polycarbonate What's better for your Greenhouse?
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16 comments

  1. where would I find a Monticello greenhouse and what would the price be for a 8×10

    1. Greenhouse Emporium

      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”.

  2. KATHRINE PAPADOPOULOS

    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

    1. Greenhouse Emporium

      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.

  3. 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?

    1. Greenhouse Emporium

      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.

      1. You mention adding accessories to keep temp at a good level. What accessories are you meaning?

        1. Greenhouse Emporium

          For winter: Heating
          For hotter days: shade cloths, ventilation, maybe even a misting or evaporative cooling system depending on how hot it gets inside.

          1. 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.

          2. Greenhouse Emporium

            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).

  4. 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.

    1. Greenhouse Emporium

      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!

  5. Hazel Buxton

    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.

    1. Greenhouse Emporium

      Thanks, Hazel! Glad we were able to help you. We are looking forward to hearing about your project.

  6. 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?

    1. Greenhouse Emporium

      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.

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