Greenhouse & Indoor Gardening

The 10 Biggest Misconceptions about Greenhouse Polycarbonate

I get a lot of phone calls and emails asking about polycarbonate including what it is and how to install or store it. There is so much confusion surrounding this subject. The objection of this article is to clarify these points.

Greenhouse Polycarbonate is Crystal Clear Like Glass

This is incorrect. Twinwall or triplewall polycarbonate is used for greenhouses. The easiest way to describe it is to envision looking down the end of a cardboard box. There is a sheet on the outside, a sheet on the inside and a rib that runs directly between these two sheets. Although the exterior sheets both have glass like clarity, the center rib will distort your view. You will see colors, but not forms clearly.

Greenhouse Polycarbonate is Difficult to Cut

No, it isn’t. The sheets can be cut with a circular saw, a table saw, even a jig saw with a fine tooth blade. Simply cut it as you would a sheet of plywood. If you would like, you can use compressed air to remove any dust from the channels.

Greenhouse Polycarbonate Can Be Stored in Direct Sunlight for an Extended Period of Time

Please do not do this because there is a protective film on the sheets. This is for protection during transport and also to direct you which side of the sheet needs to go out to the sun (UV protected). If you leave the sheets uncovered in the sun for an extended time, the protective film will melt into the sheets and become impossible to remove.

Greenhouse Polycarbonate Can be Bent in a Tight Circle

Incorrect again, there is a minimum bending radius specified by each manufacturer for each thickness of sheet. Please be sure to request this information if your design calls for bending of sheets.

The Sheets are Heavy and Difficult to Handle

Nope. A 4′ x 12′ sheet of 8mm clear twinwall polycarbonate will weigh approximately 20 pounds.

Silicone Needs to be Used on All Polycarbonate Joints

Not necessary. The profiles that come with the sheets (H, U, R and F) all fit tightly and do not require silicone when installed according to manufacturer’s specifications.

Sheets Do Not Need to Cover the Entire Roof Length and Can be Joined Together with an H Profile Running Horizontally

This is the worst offense of all. Your roof will leak at this joint, and become a moldy mess. Please be sure to order your sheets for the entire length you will need.

Sheets Can Run with the Ribs Running Vertically or Horizontally

NO! The sheets must be run with the ribs vertically so that any condensation which forms in the channels can drain.

Greenhouse Polycarbonate can be Laid Flat

Nope! You must have at least a 1 on 12 roof pitch, or 5 degree slope. Many have tried going flatter and many have been unhappy when their roof leaks. There is no way to fix this and no way around this rule.

Greenhouse Polycarbonate Will Only Last a Couple Years

Not true. Most manufacturers supply a ten year warranty on the material. Some even have 15 year warranties now. Polycarbonate typically exceeds the warranty period while still performing and looking good.

In my opinion, polycarbonate is the top greenhouse glazing material available. Just follow some simple rules while installing, and you will have a comfortable, functioning, beautiful greenhouse for years to come.

Tammy Wylie has been selling and installing greenhouses since 1993. She currently owns and operates two greenhouses. She also tests new greenhouse products and evaluates them for efficiency and user friendliness. She is the owner of Advance Greenhouses

Related Articles & Free Email Newsletters

How to Calculate Polycarbonate Sheets for a Greenhouse

Use These Cold Frame Greenhouses to Extend Your Growing Season

Understanding Polycarbonate Greenhouses

Subscribe to our Free Email Newsletter

Comment here