Which thickness, color, etc should I choose? This is a question that I get asked regularly. It was not so difficult in 1993 when we started dealing with polycarbonate. We had a local business where we sold and installed at that time. We were in the South, so all our projects were done with 8mm clear twinwall. There really were only 2 options readily available at that time – 8mm twinwall and 16mm triplewall. Mostly the 8mm was used in warmer climates and 16mm was used in cooler climates. But all that has changed now.
Always be sure to use polycarbonate sheets that are UV protected one side for any outdoors project such as a greenhouse, patio cover, etc. That is what contributes to the longevity of the sheets.
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What sheets are available?
Today you can get polycarbonate sheets in 6mm (1/4”), 8mm (5/16”), 10mm (3/8”) 16mm (5/8”) and 25mm (1”). Sheets are available in clear, opal, bronze and specialty coatings. These specialty coatings provide properties such as diffused light. I will break it down more sheet by sheet.
What is the difference between the thicknesses?
The different thicknesses will have different properties such as light transmission, etc. But the difference is also in the amount of framing you will need under the sheets. The strength in your structure is really coming from the framing, not so much from the sheets.
You should be able to get a chart like the one below from the dealer you are working with. This will show you the purlin spacing in a rafter and purlin roof design. You will see that as the snow load goes up the frame spacing can be further apart for the thicker sheets.
Purlin Spacing for Polycarbonate Sheets
Also, the thicker the sheet and the more walls – the higher the R value or insulation factor. If you are in an area where heating costs are a concern you will want to get the highest R value for your budget. That is unless you do not plan on heating your greenhouse in the winter. Then the R value is not that much of a consideration.
What is the difference between the colors?
Clear sheets will have the most light transmission and are the choice for a greenhouse unless you are using a specialty sheet such as Polymatte, Polycoolite, Lexan Softlite or Polisoft. These preceding 4 named sheets all supply 100% light diffusion with a light transmission comparable to clear. With 100% light diffusion the light is spread so that it reaches all parts of the plant equally, even under the plant canopy. This leads to higher production and a healthier plant.
Opal and bronze sheets do not have enough light transmission for a greenhouse unless you are growing plants with low light requirements. They are better off being used for patio or pergola covers. Remember, if you are covering a pergola the sheets need at least a 1 on 12 roof pitch. You cannot lay them flat.
Which thickness should I use?
Now you not only need to consider the thickness you will also have the option of how many walls. A twinwall sheet has two sheets on the outside with a rib running straight between them. A triplewall sheet will have an interior wall running parallel to the two exterior sheets. Also, when you get into polycarbonate sheets with 5 or more walls you may sometimes have an X shaped configuration.
6mm twinwall – This is an excellent choice for a patio cover, etc as you are not so worried about a higher R value on this project. It is also an excellent choice for a greenhouse in a warmer climate. Although I prefer the 8mm twinwall as it typically has an anticondensate coating on it. This is a coating that allows condensation to sheet off rather than come off in droplets. Healthier plants are the result of this. But, if the budget does not permit the 8mm, the 6mm is your next best bet.
8mm twinwall or triplewall – This is my choice for greenhouse glazing in a warm climate. It has the anticondensate coating as previously mentioned and all the profiles are readily available for it. The 8mm triplewall will have a higher R value than the 8mm twinwall. It will be a comparable value to a 10mm twinwall sheet.
10mm twinwall or triplewall – 10mm sheets do not require framing to be spaced as close as the 8mm sheets. So, if you are in a moderate climate with a small amount of snow this would be an option to consider. The triplewall sheets will have a higher R value than the twinwall sheets.
16mm triplewall or 5 wall – These are both excellent options for greenhouses for cold weather climates with a heavier snow load. Remember to build your frame with appropriate spacing as per the chart above. The 5 wall will have a higher R value than the triplewall.
16mm 5 wall polycarbonate
25mm 3 wall – If you want to go even higher with the R value, this would be your choice. Please keep in mind though that typically you will have to use the aluminum profiles with this sheet. Polycarbonate profiles for 25mm are not readily available. The only real difference in the profiles is the look and the fact that the pricing will be higher for the aluminum. Just keep that in mind when you are looking at your budget.
Polycarbonate can be difficult to work with the first time you are using it. I think that most people tend to over think it some. There are a few basic installation rules that you must follow, but it is not all that complicated. There are a lot of options today and a lot of decisions to be made, more than when we started using it. Hopefully this breakdown will simplify this process for you. The biggest mistake is getting overwhelmed before you start and not getting your project done. So just take it step by step and enjoy your greenhouse when it is completed!
Polycarbonate Sheets, Not Just for Greenhouses Anymore
Many uses for Polycarbonate Sheets
Want an easy to use building material with superior qualities? Time to try polycarbonate for your next building project.
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What is Polycarbonate?
Polycarbonate is a plastic material. It is used in many different formulas for many different applications. It is used for eyeglasses, auto parts, bulletproof windows and even for CD’s (compact discs).
8mm clear twinwall polycarbonate
We are going to be discussing multiwall polycarbonate. That is a polycarbonate sheet that is made up of multiple layers.
One of the more popular configurations is an 8mm twinwall. That means there are 8mm’s (3/16”) between the two outside sheets. It is kind of like looking at the edge of a cardboard box. There is a sheet on each side with a rib running between the two sheets. The rib is straight between the two sheets, not wavy like it is in a cardboard box.
You can get sheets anywhere from 4mm to 25mm and sometimes even thicker in the multiwall configuration. Many sheets are also available with a third wall, such as 8mm, 10mm, 16mm and sometimes 25mm. There are also sheets that have an X between the sheets going anywhere up to a 7 wall material.
The sheets are readily available in clear, opal (or ice), bronze, with specialty coatings such as Polycoolite or Softlite. A clear sheet of 8mm will have crystal clear sheets on both sides. But, you will not get a clear view through the 8mm panel. That is because the rib will distort your view.
Benefits of Polycarbonate
Polycarbonate is a lightweight material, which makes it easy to work with. For example, a 4’ x 8’ sheet of 8mm twinwall weighs only about 13 pounds.
It cuts easily with a skill saw, table saw, jig saw, etc.
It can be bent within certain limitations.
It has a high light transmission with a higher insulation factor than glass.
Polycarbonate sheets will last a long time. They will have anywhere from a 10 year to 20 year warranty depending on the material and the manufacturer.
It is great for areas with high traffic where breakage may be a concern. The manufacturers typically offer a 10 year warranty against hail damage, as it is so tough to break.
Polycarbonate can be easily installed on wood or metal frames.
The polyfilm will not last as long as the other 2 options. The 4 year refers to the length of the UV protection. If you get the full 4 years you will definitely not get much more. The polycarbonate sheets will have a 15 – 25 year lifetime depending on the manufacturer and the sheet. Tempered glass will last pretty much forever unless it is broken.
Many people choose a specialty sheet for their greenhouse such as Polycoolite or Softlite. Polycoolite will help to keep your greenhouse cooler in warm climates.
Softlite or Polymatte both offer 100% light diffusion. This means that the light is scattered all through out the greenhouse so that all parts of the plant, even under the plant canopy, get good light.
Bronze and opal are not recommended for greenhouses as they have low light transmission. You would only use them for plants with low light requirements.
A conservatory is much like a greenhouse, but it is typically meant for more of a living space rather than a space for plants. These may or may not be attached to your home.
Polycarbonate Wrap Around Porch
Polycarbonate is an excellent choice for a patio cover. You can choose between clear, opal, bronze, or specialty sheets designed to keep out heat. The main benefit of polycarbonate over solid materials is that it lets light into your home and does not darken it like solid materials can.
Polycarbonate can be used for skylights in homes, or even commercial skylights. There is even a polycarbonate panel that is made with a standing seam for commercial skylight applications. This totally eliminates the possibility of leaking around the seams. You would have to have several inches of rain standing on your roof for it to get to the seams.
2 UV Polycarbonate Fencing
Polycarbonate is an excellent material for fencing. It gives you privacy, but you can still get your sunlight in. You must be certain to use 2UV polycarbonate for fencing. This is a sheet that has UV protection on both sides of the sheet. This is because both sides of the sheet are exposed to sunlight. The UV protection is what gives this product its longevity.
Polycarbonate Office Partition
Who wants to spend the day in a dark, closed in cubicle? No need to do that anymore. Polycarbonate will give the needed privacy while lightening things up.
Polycarbonate Hurricane Panels
Having spent more than 15 years in a hurricane area, I can tell you that hurricane panels are a great invention.
Plywood is heavy and it will darken your house. Chances are that if a storm hit you may be without electricity. This means you can’t even see to make your way around in your house. Sometimes there are back to back storms and you don’t want to remove the covers and have to reinstall them.
Polycarbonate hurricane panels are lightweight and easy to handle. Plus they will let the light in. If there is an active hurricane season you can even leave these on for an extended period of time.
Polycarbonate sheets can also be used to cover a portico to a commercial building such as a hotel. The guests will be protected from the weather, and still have plenty of light. This is just more inviting than a dark, solid cover.
In conclusion, polycarbonate is a versatile, easy to use material. What can you think of to build that I did not mention? Let us know in the comments below.
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The first time we installed polycarbonate was in 1993. Our “cell” phones were called transportable phones. It was about like hauling a suitcase around. There was no internet. No way to search for instructions on how to install polycarbonate sheets. No YouTube videos! Can you imagine. So, we had to learn the hard way by trial and error. Thank goodness we have more sophisticated tools available now. Most people will have a lot of questions when installing polycarbonate for the first time. It is not all that difficult. I think it is just the fact that it is a new material.
Written by our own Tammy
What is Polycarbonate?
Polycarbonate is a rigid plastic. The polycarbonate used for greenhouses is typically a multiwall. This means that there are 2 exterior walls, possibly some interior walls, and ribs that run between these walls. You cannot see clear through this like looking through glass.
Looking at a piece of polycarbonate is kind of like looking down the end of a cardboard box. A sheet on the outside, a sheet on the inside and a rib running between them. If you peel the layers apart you will see that they are all clear, but the rib that runs in the center is what distorts your view.
What parts are needed?
• Polycarbonate sheets – they are available in 4′ or 6′ widths and in lengths anywhere from 6′ to 48′ if needed.
• U channel – sometimes called J channel. This is available in either aluminum or polycarbonate. It is used to seal the channels at the top and the bottom of the sheets. You will drill 1/8″ holes every 1 – 2 feet on the bottom U. This is so that any condensation in the channels will be able to drain.
• Screws with neobonded washers – You will need screws to fasten the sheets to the framing. You will also need to use a flat washer that has a neobonded side for this material.
• Tapes – There are aluminum or foil and vent tapes. You place the foil tape under the U at the tops of the sheets and the vent tape under the U at the bottom of the sheets.
• Side by side fasteners. This is the part that joins the polycarbonate sheets side by side. There are several different options for this.
1. Polycarbonate H – this is the part that slides between the sheets and fastens them side to side. It is made of polycarbonate and is a one part system. You install this by installing your sheets loosely and sliding this from the bottom of this joint all the way to the top.
2. Polycarbonate base and cap – This system consists of 2 parts – a base and a cap. The base is screwed down to the framing. The sheets are placed over the base. The cap is “snapped” into place using a rubber mallet. The base and cap have an interlocking mechanism that keeps it tight. This is considerably easier to install on longer sheets.
3. Aluminum Base and Cap – This is the same as the polycarbonate base and cap. The exceptions are that they are made from aluminum and the cap screws into the base rather than being “snapped”.
1. Make sure that you have purchased greenhouse polycarbonate that is UV protected on at least one side. This is the side that will be out toward the sun. The UV protection is what gives the polycarbonate its extended life. Polycarbonate sheets with UV protection will carry a 10 – 20 year warranty. Expect at least a 15 year lifetime out of this material.
2. Make sure that you have ordered all of the materials you need. Polycarbonate ships on Common Carrier and it can get expensive if you have multiple shipments.
3. Do be prepared to unload when the delivery is made. You may have a forklift, or you may have ordered a power lift gate. Just remember, you are responsible for unloading. It is the drivers responsibility to get the package to the back of the truck.
If you are going to open the crates and hand carry the sheets, make sure you have the tools to do this. The bulk of the weight is in the crate. The sheets are lightweight and easy to handle. I recommend having a pair of tin snips (in case the crate is banded), a hammer, a crowbar, a drill with screwdriver bits, and a helper. This goes better with 2 people.
4. Do not store your sheets in direct sunlight. The protective film will melt into the polycarbonate panels. You will never be able to remove it once this happens.
5. Make sure that you have built an adequate frame for your weather conditions. You should have rafters and purlins in your roof structure. The manufacturers have charts that will show you proper spacing.
6. Do not remove the protective shipping cover until you are ready to install. This will have the label telling you which side is UV protected. Once you remove this film you will not be able to tell which side should go to the sun. If the sheet is flipped over you will not get the longevity out of the sheet.
7. Do not stress over cutting these sheets. They cut much the same as a sheet of plywood. Leave the protective film on so you don’t scratch the sheets. Mark your chalk line. Cut with a skill saw, table saw, etc. If you get filings down in the channels you can use compressed air to blow them out.
8. Do not ever run the ribs horizontally, EVER! There will be no way for any condensation which may form to escape. This will result in the moisture accumulating between the ribs and eventually getting moldy.
9. Do make sure that you have purchased sheets that will reach the entire length that you need. Don’t ever try to splice sheets with a horizontal H. NEVER! The structure will leak at this point. Also, you will end up with the same moldy mess in the H profile because your water has no way to get out.
10. Do be sure to allow for contraction and expansion. You should allow 1/8″ per 3′ for contraction and expansion.
11. Do be sure to predrill your screw holes slightly larger than your screws. This will also allow for the contraction and expansion of polycarbonate sheets. Using the neobonded washer will keep your structure from leaking at this point.
12. Do not install polycarbonate sheets on a flat roof. A minimum of a 1 on 12 roof pitch is required. If you do not do this you will have leaks at the H profiles.
13. You can bend polycarbonate sheets, but there is a minimum bending radius. Manufacturers will have charts letting you know what this minimum bending radius is.
14. Do not silicone all of your joints. Polycarbonate needs the freedom to move due to the contraction and expansion of the material.
15. Do not try to cut angles for both gables out of the same sheet unless you have room to cut from the same side. Many builders will make their cuts on plywood and then flip the one side to install to save on materials. If you do this with polycarbonate sheets (UV on one side) you will have one side that is protected and one side that is not.
Polycarbonate may be confusing at first, but if you follow these few simple steps you will end up with a professional installation that will last you for years. Relax and enjoy your new greenhouse, patio cover, fencing (use 2UV for this) or swimming pool cover!
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So, you have decided to build a greenhouse, but you are confused about which type of greenhouse covering would be best for you. Let’s take a look at some of the pluses and negatives of polycarbonate sheets and polyfilm coverings. We will discuss R value, installation, cost and lifetime expectancy.
R value is defined as a materials ability to resist heat flow. The higher the R value, the less energy it will take to heat the same size space under equivalent conditions. This may or may not be a concern to you depending on how you are going to use a greenhouse.
The most common single film used for greenhouses is clear 6 mil, 4 year covering. What this means is that the film is 6 mil thick and that the UV protection is warranted for up to 4 years. There are also some other types of film such as overwinter (this film is meant to last one year), white films (lower light transmission) , and reinforced polyfilm (with a rip stop cord).
The R value of single polyfilm is 0.87. It is the least efficient of all of the greenhouse coverings we will discuss.
Installation can be done in several different ways. If you have a wood frame you can use batten tape and staple through the cover and the tape into your frame. If you have a wood frame or a metal frame you can use the base and wire system. The base is screwed to your frame and the cover is secured using a W or wiggle wire. This is a pretty simple installation, but you want to make sure that you do not try to do this on a windy day. You will need several people to do this depending on the size of the greenhouse.
The single polyfilm will be the least expensive of all of the coverings we will discuss.
This film should last you the 4 years that the UV covering is guaranteed for. The only issue with this covering is that you may get a tear. There is repair tape available for this. But, if you are not there and not able to fix a tear in a timely manner you may lose the entire cover. This is why some people will choose to go with the reinforced polyfilm over the clear 6 mil, 4 year. It has a rip stop cord that will keep a tear from spreading. That way you will be able to fix the tear no matter how soon you are able to get to it.
Reinforced Polyfilm with Rip Stop
You can do a double polyfilm greenhouse a couple of different ways. You can just buy 2 pieces of the film and attach them together. Or, the easiest way to do this is to buy a tube of the polyfilm. This is just a double layer that is already fastened together. The base and wire system is set up to hold up to 6 layers, so this is not an issue. You will also need a poly inflation fan kit to inflate the 2 layers. I have had some people mention that they think this makes the cover tighter and less susceptible to tears. I have no proof of this, but it does seem a logical conclusion.
The R value of double polyfilm is 1.7. This will save you 40% on the energy costs over a single layer of polyfilm.
The installation on this is done in the same manner as a single layer of polyfilm.
This film will basically be twice the cost of the single polyfilm, as you are basically just using a double layer of the same material. You will have the additional cost of the blower fan. These are typically around $200 or less, depending on the size of the greenhouse and the size of the motor needed.
This film may last a little bit longer than the single layer. As I stated earlier some claim that they inflation keeps the film from tearing as easily. The UV protection is rated for the same amount of time as the single polyfilm.
Polycarbonate is the greenhouse covering of my choice. It fits my needs the best of all of the materials. However, a lot of people don’t like it because of its appearance. It is a rigid plastic configured in much the same way as a piece of a cardboard box. It has a sheet on the outside, a sheet on the inside and a rib that runs through between the 2 sheets. The rib in polycarbonate will be straight vs the wavy rib in a cardboard box. This will distort your view. You will be able to see color, but you will not see form clearly. I use the example that you can see a green leaf and a red flower, but you will not be able to make out if it is a poinsettia, geranium, impatiens, etc. Of course the clear polyfilm is not exactly clear either. It will have a hazy type of appearance to it. If you want a clear glass like view, tempered glass is your only option.
Polycarbonate sheets are available in several different thicknesses. 8mm clear twinwall will have an R value of 1.8. 16mm clear triplewall will have an R value of 2.4. This will be the most efficient of the coverings we are discussing.
Installation of this material requires polycarbonate H profiles to join the sheets side by side and polycarbonate U channels to close off the ends. You will need more framing for this material vs polyfilm greenhouses. Typically polyfilm greenhouses will have 4′ or 6′ wide spaced bays. You can do the same with the polycarbonate, but you will need to run purlins between the rafters spaced according to your snow load needs. There are charts available to determine this. You can typically install this with 2 people as the sheets are not heavy and you install one 4′ wide or 6′ wide sheet at a time. You still do not want to try to install under windy conditions as the sheets can be caught by the wind and sail away.
This will be the most expensive of the coverings discussed in this article. But, it will be the longest lasting. Depending on the manufacturer polycarbonate sheets have between a 10 year and 20 year warranty on the UV. Most sheets also have a 10 year warranty on hail damage, so no need to worry about tears. The practical life expectancy of this material is 20 – 25 years.
When considering which of these materials to use to cover your greenhouse you should look at the initial cost, the cost to install, the cost to heat the greenhouse, and the life expectancy of the material. Once you have made these decisions you should be able to choose the best covering for your greenhouse with ease.
Greenhouse Glazing Materials, Warranty vs Life Expectancy
I get asked a lot about how long certain greenhouse coverings will last. The thing is, the limit of the warranty does not equal the life expectancy of the material. I will address the following materials – 6 mil, 4 year polyfilm, reinforced polyfilm and polycarbonate sheets. I will be mentioning the UV protection. That is what keeps the materials from getting brittle, cracking, or turning yellow. The warranty will typically cover how long the manufacturer expects the UV protection to last, or it may refer to how much the UV protection may change in a certain period of time.
Greenhouse polyfilm is typically listed by the thickness and the length of the time that the UV protection is warranted for. 6 mil, 4 year polyfilm is 6 mil thick and has a UV protection that is warranted for 4 years. But, that does not necessarily mean that it will last the entire 4 years. The material will not get brittle, etc, but if it is damaged (due to a falling limb, hail, etc) there is a possibility that the cover will be lost. There is patching tape for the film coverings, but if you are not at the greenhouse when the damage occurs it may be too late to stop it. This will be the least expensive of the greenhouse glazing choices and is excellent for small hobby or commercial greenhouses. Although most of the commercial greenhouses will use a double layer of this film with a blower that blows air between the 2 layers. This will definitely increase the insulation factor for this material. I have had some growers report back to me that they feel the film is less likely to be damaged when using this double layer. They feel that the air between the layers “stretches” the film, making it tighter and less susceptible to damage from falling items.
The reinforced polyfilm is 2 layers of film laminated together with a rip stop feature in between the sheets. This has a one year warranty on the UV protection. But, we have had reports back from people who have gotten up to a 12 year lifetime from this material. The rip stop feature is what makes this possible. If the film does get a tear it cannot go any further than the cords of the rip stop. That will keep the area of the rip limited, and it is easily repairable once it is found.
Polycarbonate sheets are a rigid material. Many manufacturers offer a 10 year warranty that the light transmission will not vary more than 10%. The change in the light transmission is what causes the sheets to get brittle, yellow and crack. There are, however, some manufacturers out there now offering a comparable 20 year warranty. Please be sure to check with the company supplying you the sheets to see which warranty is offered. Polycarbonate is a tough material and typically has a 10 year warranty against hail damage. So, tearing or damage to the sheets is not near as big an issue as the polyfilm. In fact I have been dealing with polycarbonate sheets for over 20 years now and have never been involved in a warranty claim. I have had many people in the industry report back that they have seen polycarbonate sheets (with the 10 year warranty) last up to the 20 year mark. I personally have seen the 10 year warranty material remain usable at 15 years.
Hopefully this overview of the warranties and greenhouse glazing materials will give you the information you need to make the best decision for your greenhouse.
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