Polycarbonate Sheets – 15 Great Installation Tips

Installing Polycarbonate

15 Great Tips for Installing Polycarbonate

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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”.

Installation Tips

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!