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How Thick Should Polycarbonate Be For A Greenhouse?

Various Polycarbonate panels of diverse thicknesses and the text: How Thick Should Polycarbonate Panels for Greenhouse be?

Table of Contents

Polycarbonate is the most popular choice for greenhouses nowadays. It has many advantages from light-diffusing properties to durability. The question is, though, how much influence does the thickness of the Polycarbonate have.

Choosing the right panel or the right greenhouse kit that features the thickness you want can get difficult. There is a wide variety of panels and kits to choose from and it all depends on your greenhouse structure, climate, and budget.

Polycarbonate is a strong, durable, and flexible thermoplastic. This material is malleable and can be prepared to fit any purpose. These features make Polycarbonate a better option than other alternative coverings.

Skilled installation of panels with a precisely chosen material, including size, thickness, color, and the manufacturer, will act as an assurance for the long and fruitful performance of your greenhouse.

Some misconceptions about Polycarbonate on greenhouses

Before we start with the insulation factors and other things, we want to clear up a few things. There are a few misconceptions that we keep hearing from our customers.

Polycarbonate is transparent like glass

This is absolutely wrong. There are no high-quality Polycarbonate panels that you can see through like glass. That transparent material is acrylic. Polycarbonate panels are translucent (as in: let sunlight through) and it’s not completely opaque.

Depending on the brand and product, Polycarbonate can be less or more see-through. Some manufacturers even create panels specifically for more privacy or for more light diffusion.

Polycarbonate greenhouse and panels with the text: Polycarbonate - How Thick does it need to be for greenhouses?

Thicker Polycarbonate provides more insulation than thinner ones

This is actually the most common misconception about greenhouse insulation. Insulation is NOT ONLY coming from the panel thickness. It also has a lot to do with the greenhouse structure and the quality of the panel itself.

The tighter the greenhouse is constructed (maybe even with rubber seals between framing and panels), the better it is insulated. So, it’ll be cooler in summer and warmer in winter.

On another note, Solexx panels are thinner than most greenhouses but they still provide a better insulation factor than 8 mm twin walls.

Winter insulation is the most important part

Another thing people don’t think about is the heat. People are concerned about the winter but the spring and summer should concern you just as much. While you can heat a greenhouse easily, it’s harder to cool it down because greenhouses are always hotter.

Generally speaking, the thicker the panel, the more heat it traps. A warmer greenhouse doesn’t mean a fruitful harvest when it’s summer.

So, in order to truly grow year-round inside your greenhouse, you have to find ways to cool it down in summer.

Polycarbonate will discolor over time

The dreaded yellowing of Polycarbonate panels is a common worry because a lot of people have seen it themselves. However, with technological advance, this should be a thing of the past. If a panel yellows after a few years, it is a sign of defect or low quality.

While keeping this in mind, you came here to learn more about the insulation factors of the different Polycarbonate materials and their light transmission.

Characteristics of Polycarbonate panels for greenhouses

When looking at PC panels for greenhouses, you’ll notice the rectangular combs. It’s like empty spaces/tubes that run from top to bottom. It’s essentially two sheets (walls) with stabilizing walls in between. It’s like a double-pane window just with the framing in between the panes. These panels can also be designed as triple walls.

This design increases the insulation factor, stability, and effectiveness while keeping it somewhat flexible. The “air pockets” help with heat retention.

The multi-wall sheet has relatively less light transmission rate and has a less solar reflection. It is lightweight and easy to install.

It offers superb insulation to prevent the unfavorable results of the extremely intense weather. This is also an excellent crash absorber that can even endure quite a bit of hail.

Another style for Polycarbonate panels is the honeycomb design. They are less common and more expensive, but sturdier.

So, how thick should your Polycarbonate panels be?

All of 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 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 (more about this below). This is because it depends on the material and the greenhouse structure.

The insulation factor in relation to the panel thickness

Greenhouses usually demand high levels of heat retention. Polycarbonate will do a better job in comparison to glass. Insulation is measured in R- and U-values. We will explain what these mean first.

What is an R-value?

The R-value is a measurement of the insulation efficiency. The higher the number equals a higher degree of insulation. For example, one of our toughest winter greenhouses has an R-value of 2.0.

A high level of insulation guarantees that the temperatures will not climb too high in summer, or drop too low in winter.

The formula for computing R-value is R = 1/U.

What is the U-value?

The U-value shows the amount of heat loss. The lower the value, the less heat will escape.

It measures how much heat is conducted. It is commonly used in houses for door or window systems.

The formula for computing the U-value is U = 1/R (literally the reverse of the R-value). 

 Covering MaterialR-valueU-value
3mm single pane glass0.951.05
4mm double-wall Polycarbonate1.430.70
6mm double-wall Polycarbonate1.540.65
8mm double-wall Polycarbonate1.600.63
10mm double-wall Polycarbonate1.890.53
8mm triple-wall Polycarbonate2.000.50
16mm triple-wall Polycarbonate2.500.40
3.5 mm Solexx panels2.100.48
5 mm Solexx panels2.300.43

BEFORE you base your choice on the best insulation, keep reading! You may not need those thick panels because you are living in a mild-ish climate. In addition to insulation, there are other affects that thicker panels have.

What else is affected by the thickness of Polycarbonate panels

The thickness of Polycarbonate affects the light transmission, heat preservation, and conductivity, as well as UV-protection and sometimes light diffusion. These are are all features which made polycarbonate a top choice for greenhouse covering.

UV-Protection

If you look at the panel from a certain angle, you will see the protective layer. This plays a big role for UV-protection of the panels themselves as well as gardeners and plants.

The level of UV-protection varies depending on the measurement of the sheets as well as the brand. Some manufacturers put the layer on one side and others started using it on both for fewer assembly problems.

Light transmission & diffusion

With every millimeter, you will lose light transmission. Although Polycarbonate is translucent to some level, it isn’t like glass.

This means you shouldn’t go with the super thick panels if you don’t need it for extreme winters. You might as well go for 8 mm instead of 16 mm and install a heater.

Of course, the shape of the greenhouse and the width of the profiles also determine the amount of light your plants get.

Some Polycarbonate panels have extra light diffusing properties. Polycarbonate already diffuses light in comparison to glass. However, manufacturers like Solexx put a special focus on this. This becomes extremely handy for gardeners who want the best light conditions for their plants.

Stronger against wind, snow, and hail

Triple-walled Polycarbonate is sturdier compared to twin-walled panels. If you need a sturdier panel because of frequent storms and snow, we would advise choosing a thicker panel.

If you are DIY-ing your greenhouse you may need a flexible material. Thinner panels and sheets are obviously more adjustable than the thicker ones.

Should you go single, twin, or triple?

In order to give you a better idea of what you need, it may help to go through the 3 Polycarbonate thicknesses.

Single-wall Polycarbonate

Even though single-wall Polycarbonate is tougher than glass, it may not be the best choice. They don’t diffuse light or insulate heat properly. The R-value of this material is 0.83, while glass has an R-value of 0.93.

94-96% of the light reaches through a single wall which is very close to glass (97-98% passes through glass).

Single-wall Polycarbonate is not ideal for greenhouse gardeners when it comes to durability and sturdiness. Although you’ll safe money at first, you may have to renew the glazing more often.

Twin-wall Polycarbonate

Clear Twin-wall Polycarbonate on white surface

These panels keep heat confined inside your greenhouse, making it an energy-efficient alternative. Twin-wall Polycarbonate also helps carry warmth from the sun into the depths of your greenhouse so your plants can flourish. It can also provide more benefits like improved harvest, more leaf count, and shorter growth time.

Twin-wall Polycarbonate is less likely to break or bend because it has a very sturdy design.

Twin wall sheets confine air between two walls. It gives up to 50% power savings compared to single wall sheets. The air-trapping ability assures great thermal insulation. 

Triple-wall Polycarbonate

One piece of triple wall clear Polycarbonate with white background

The triple wall materials enclose more layers which are best for cold climates. An 8 mm triple wall Polycarbonate offers added insulation in comparison to 8 mm twin-wall.

Triple-wall Polycarbonate is long-lasting and generally impact resistant. They reduce light transmission by roughly 20-30%, though.

They require a higher initial investment but may be worth it for you in the long run. The enhanced insulation can end in long-term savings on winter heating expenses. 

It is particularly used in cold climates for year-round greenhouse gardening. This type of Polycarbonate can withstand massive snow loads and freezing without deformation.

How are you planning to use your Polycarbonate greenhouse? Tell us more here!

15 comments

  1. Alta De Wet _ DS De Wet School for Autism NPC

    I want to convert an old garage on the school premises into a sustainable aquaponics business, an ideal environment for our autistic learners to develop skills in gardening they love so much and employment once they finish school.

  2. Any advice for which material to use for zone 8a? New gardener looking to create a greenhouse for year round growing!

    1. Greenhouse Emporium

      Hi Alexis, we would recommend 8mm twin-wall Polycarbonate at a minimum. While you don’t have those super harsh winters, you still want to cool down the greenhouse in the warmer months. The thicker the Poly, the more insulation you will get (from both heat and cold). 8mm is the standard and works well for most areas. Anything above will depend on how much you are willing to spend on your greenhouse.

  3. Nevil Kadva

    Hi I have lots of polycarbonate panels only problem is color of the panel light smoky (gray). Should I used it for green house? Even I can used two panel one on the top that many I have. Let me know thanks

    1. Greenhouse Emporium Team

      Hi Nevil! Colored polycarbonate reduces light transmission into a greenhouse. Clear is best for greenhouse panels. If you need a shaded area with less light in the greenhouse, you may be able to use a few colored panels on the top to achieve this effect. Gray colored polycarbonate could also potentially be used if you are in a very hot and bright climate.

  4. Love this article-

    In Zone 5 is the double wall 8mm enough for snow load?

    Thank you

    1. Greenhouse Emporium

      Hi Reed! Glad you find the article helpful. The thickness isn’t helping with the snow load that much. The quality of the framing will be more important. For your zone, 8mm can work but you will have to heat a lot. If you can get thicker panels, it’ll help with the insulation.

  5. ann longstaff

    is 0.7mm ok for greenhouse walls?

  6. Hello, very helpful article. I am in the process of bulding a greenhouse. Do you think 8mm triple wall is sufficient for year round gardening and Ohio winters?

    1. Greenhouse Emporium Team

      Hi Ann, unless you are in a very hot climate 0.7mm thick Polycarbonate will likely be too thin to provide enough insulation and prevent heat loss as a greenhouse. It might work well for a cold frame shelter if you already have the Polycarbonate and want to give it a try! You can find more information on cold frames here: Why and When to use a Cold Frame Greenhouse

    2. Greenhouse Emporium Team

      Hi Melissa, 8mm will usually be sufficient for most environments. If you are able to obtain the U- and R-values for the Polycarbonate, this will also help you determine if it is a good fit for your needs. Also, be sure to look for and seal any gaps between panels and framing. This will help keep the greenhouse warm, as well as having good glazing (insulation). Best of luck as you build your greenhouse!

  7. Christopher Everett

    Hi. I want to cover the top of a Pergola with a rainproof covering. As insulation is not an issue here, can anyone advise me as to the thickness of twin wall will do the job for me. The area I want to cover is 4.5 meters x 6 mtrs with rafters at 1 mtr and noggins set at 2 mtre. The fall over the 4.5 area is 175 mm. I am under the impression that the crush strength of 4mm would be stronger than say, 10 mm. Many thanks. Chris Everett.

    1. Greenhouse Emporium Team

      Hi Chris, sounds like you have a great outdoor space and are looking to improve it! There are many options for rainproof coverings for a pergola, including waterproof fabrics and thin wall as you are considering. Do you get snow or have heavy leaf fall that would accumulate? The weight the cover would need to withstand will be important in determining what thickness is needed.

  8. Alan Wayler

    I’m building a shed roof greenhouse in Vermont. Size 8’x9’ with good pitch roof. Have settled on 8mm insulated polycarbonate for walls. Prefer to do roof in clear polycarbonate but would like recommendation on thickness to handle snow load. Single sheet vs double walled? Structure framing is all wood. Roof has good pitch. Greenhouse will be used between March-November.
    Appreciate your help b

    1. Greenhouse Emporium Team

      Hi Alan! This is a tough one to answer without more specifics. We recommend you consider the overall average snowfall, the exact roof pitch, and how long snowfall will remain on the structure. Will the pitch be enough that the snow will slide off and not accumulate? Are multiple snowfalls that accumulate with ice between the layers, making it heavier, common? These are things to consider. This far north, we recommend a double wall (twin wall) or even triple if possible. Good luck with your greenhouse!

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