Greenhouse Panels and Sheets FAQ

Greenhouse Panel Properties

We received many questions about polycarbonate sheets and how to install them everyday. We have compiled this list of FAQ to hopefully help you figure out this product. See our main polycarbonate page with our products here.

What are polycarbonate sheets used for?

There are many uses for polycarbonate sheets. They are known for being used in greenhouses, but they can also be used as patio covers, hurricane panels, conservatory roofing, cubicle dividers, skylights, exterior fencing (you must use the 2UV product for this application), and for a portico.

Are polycarbonate sheets strong?

The panels are virtually unbreakable. They have an impact strength 200 times greater than glass, 8 times greater than acrylic.

How much does a polycarbonate sheet weigh?

Polycarbonate panels are lightweight and easy to handle. For example a 4′ x 8′ sheet of 8mm twinwall will weigh about 13 pounds. A 4′ x 8′ panel of 16mm triplewall will weigh about 23 pounds.

Can you bend the panels?

Yes, you can bend the greenhouse panels. Your distributor should be able to supply you with a manufacturer specified table such as the one listed below. How much you can bend the sheet depends on how thick the sheet is.

Is it safe to walk on polycarbonate sheets?

You should never put your full weight on a polycarbonate sheet. It is not meant to support body weight. And, it can be slippery. You should always be supported by the framing material if you need to be on the roof. Use stepladders or walk boards for support.

Can you drill through polycarbonate sheets?

Absolutely. In fact you are required to predrill your screw holes slightly larger than your screws to allow for contraction and expansion. You can use a power drill with standard high speed twist drills.

What is the difference between twinwall, triplewall or 5 wall polycarbonate sheets?

A polycarbonate sheet is like looking down the end of a cardboard box section. There will be a sheet on the outside, a sheet on the inside and a rib that runs between the 2 exterior sheets. The rib in polycarbonate is straight rather than wavy like in cardboard. A twinwall sheet will have only the 2 exterior sheets. A triplewall sheet will have another sheet between the 2 exterior sheets. The 5 wall sheets come in 2 different configurations. Some of them have 3 interior walls. Some have one interior wall and an X configuration.

Does polycarbonate turn yellow?

Polycarbonate sheets to be used outside have a UV protection on them. This is what keeps the panels from yellowing or getting brittle. Some sheets will have UV protection on both sides for applications such as fencing. But, most polycarbonate sheets will only have the UV protection on one side and that side should be facing the sun.

How do you cut polycarbonate sheets?

You can cut polycarbonate sheets with a jig saw, table saw, circular saw or sabre saw with a blade having 8 – 12 teeth per inch. Do not remove the  protective film prior to cutting. If any shavings get into the channels from the cutting you can blow them out with compressed air.

Can you use polycarbonate sheets for a greenhouse?

Absolutely! There are many reasons for this. Most important of all is the strength of the greenhouse panels. The sheets even have a 10 year warranty against hail damage. The panels will give you much more insulation that a glass greenhouse. The only downfall is that the ribs in the sheets will allow you to see outdoors, but you will not have a clear view. I say that you will see a green leaf and a red flower in the greenhouse, but you won’t be able to make out if it is a poinsetta, a begonia, impatiens, etc.

What thickness of polycarbonate should I use for my greenhouse?

There are a couple of factors to decide this. What is your climate and how warm do you want to keep your greenhouse in the winter. When we started installing polycarbonate we basically had the choice of 8mm twinwall and 16mm triplewall. Of course today there are many more options like 10mm twinwall, 8mm triplewall, 10mm triplewall, etc. Not to mention the specialty sheets. My rule of thumb has always been 8mm greenhouse panels in the South and 16mm in the North. This is presuming that you are going to heat your greenhouse in the winter. This is not a steadfast rule of thumb, rather just a guide.

How long do polycarbonate greenhouses last?

Some polycarbonate sheets have a 6%, 10 year warranty. This means that the sheets will not vary more than 6% in light transmission in 10 years. We are seeing a 15 – 20 year life span on these sheets. There are also some Lexan sheets which have a 2%, 20 year warranty. These sheets are purported to have a life expectancy of 25 year.

Do I need to seal the ends of polycarbonate sheets?

Yes! You should put foil tape under a U at the tops of the sheets with the vent tape under the U at the bottom of the sheets. You should also drill 1/8″ holes in the bottom of the U at the bottom of the sheet.

Can I use silicone on polycarbonate?

If you are using the polycarbonate profiles to connect your sheets there is really no need for silicone. You should never stiff fix your polycarbonate sheets. That being said if you need a little bead of silicone in a corner or some such application you should use 100% silicone that does not have a PVC base.

Why do you have to predrill polycarbonate sheets?

Polycarbonate will contract and expand with heat and cold. You need to leave room when you are installing to allow for this. Allow 1/8″ for every 3′ for contraction and expansion. You will also need to predrill you holes for your screws to allow for the contraction and expansion. Use a drill bit just slightly larger than your screw and drill through the polycarbonate sheet only. Do not predrill through your frame.

Why do I need to use a neobonded washer when installing polycarbonate?

You need the neobonded washer to cover where you predrilled your holes for contraction and expansion. If you do not use this you will have leaks around the screw.

What are the disadvantages of polycarbonate?

The main disadvantage of using polycarbonate sheets is the fact that you loose your clear view. The sheets on the exterior and interior are clear, but the ribs that run through between the greenhouse panels will distort your view. I always say that you can see a red flower and a green leaf, but you cannot make out if it is a poinsetta, begonia, impatiens, etc.

How would you describe a twinwall polycarbonate sheet?

A twinwall polycarbonate sheet is like looking down the end of a cardboard box. There is a sheet on the outside and a sheet on the inside. There will be a rib between these 2 sheets. In cardboard the rib is wavy. With the polycarbonate sheets the rib goes straight between the exterior sheets.

What is the difference between corrugated and multiwall polycarbonate sheets?

Here is the snag with this one. Some people use corrugated and multiwall interchangeably, so don’t get confused by that. The corrugated sheets are a single sheet with a greca profile. They do not have profiles to connect them side by side. They are 50″ wide and overlap for a coverage of 48″ per sheet. The multiwall sheets are flat on the sides. See previous answer for a description of multiwall. They will have H or base and cap profiles to connect the sheets side by side and a U channel to close off the channels. Multiwall sheets will have a better R value (better insulation). Also, typically the corrugated sheets will only have a 5 year warranty where the multiwall sheets will have anywhere from a 10 to a 20 year warranty.

What is the advantage of an anticondensate coating?

The anticondensate coating is a coating that is found on the interior wall of some polycarbonate sheets. In certain conditions your greenhouse will have moisture gather on the interior roof. The anti condensate, or anti fog, coating will cause the condensation to sheet off rather than fall of in droplets. This leads to healthier plants.

Do I install my sheets tight or do I allow room for contraction and expansion?

You absolutely allow for contraction and expansion. You should check with the manufacturer of the sheets, but a good rule of thumb is to allow 1/8″ for every 3′.

What is the difference between a rafter and a purlin?

Rafters are framing members that run vertically. Purlins run horizontally. See drawing.

Raters vs purlins for polycarbonate installation

I see sheets with diffused light. What does that mean?

Diffused light is basically light which is scattered to reach all parts of your plant. This will cause a healthier,  more productive plant as all parts, even under the canopy, are receiving equal light.There will be no shadows when using sheets with diffused light.

What properties should I consider when purchasing polycarbonate sheets?

You will see a lot of numbers when researching polycarbonate sheets. See the list below for the most commonly found properties.

· R-value: R value is an indication of the insulating factor of the material. A higher R is better insulation.
· U-value: U-Value is the measure of the rate of heat loss through a material. Look for the lower U value for a more efficient material.
· Weight: Polycarbonate is a lightweight material. A 8mm sheet typically weighs about .41 pounds per square foot or a total of about 13 pounds for a 4′ x 8′ sheet.
· Gauge: This is just telling you how thick a sheet is in inches. For example, 10mm is 3/8″.
· Light transmission: The maximum transmission in the visible light region. Single glass has a 90% light transmission. 8mm polycarbonate has around 80% light         transmission. You can go down as low as 60% and still grow plants in that environment.
· Shading coefficient: This is a measure of the total amount of heat passing through the polycarbonate compared with that through a single clear glass.
· Solar Heat Gain Coefficient: This measures how well a material blocks heat from sunlight. The lower a SHGC, the less solar heat it transmits.
· Solar Reflection: This is just like it sounds, the amount of sunlight reflected off the sheets. The higher the number the cooler the structure will be.

Why is the film covering on my polycarbonate sheets?

The film is there for 2 reasons. It will protect the sheets in transit and while cutting. Also, one side will be marked showing that it is the UV protected side. That is the side you want to face the sun. Do not remove the protective film until you are installing each sheet.

If I have removed the protective covering is there any way that I can tell which is the UV protected side?

The best idea is to not remove the film until you have each sheet to the spot where it is going to be installed. Some manufacturers use a tint that can be seen with a black light. Some print their name on the edges of the sheets. If you can read the name you have the sheet in the proper orientation. If the sheet is upside down the name will be too. Still, the best practice is to not remove until you install.

Why shouldn’t I store my sheets in direct sunlight?

If you store your sheets in direct sunlight the protective film will melt into the sheet. It will become impossible to remove.

How do I clean my polycarbonate greenhouse?

Use a soft rag or sponge that is free of any debris that may scratch the sheets. Use a mild household detergent such as dawn dish washing liquid.

Which way do you run the flutes in a polycarbonate sheet?

Always run the sheets vertically. Always use one sheet the entire length that you need. Never try to splice pieces with a horizontal joint.

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Is the foil tape and vent tape required for proper installation?

Yes, foil tape should be put underneath  the U’s at the tops of the sheets. Vent tape should be put under the U’s at the bottom of the sheets.

Are there special profiles to install polycarbonate sheets?

Yes, there are pieces to connect the sheets side by side. These come in several different configurations. There is a one part polycarbonate H, a polycarbonate base and cap and an aluminum base and cap. Also there is a U profile to put at the tops and bottoms of the sheets to close off the channels.

How do I store polycarbonate sheets?

Sheets should be stored in an area away from direct heat or light. Sloped stacking is the recommend method of storing, but you can stack the sheets up to 3′ high on a surface that is flat and supported.