Build Your Own Greenhouse – How to Figure How Many Polycarbonate Sheets and Profiles I Need?

I get a lot of questions about how to figure the polycarbonate sheets and profiles needed to build a greenhouse. I have found that the best way to handle this is to break the project down into sections. You would figure each section and then add them all together to get your final bill of material. I will show you an example of how I would figure a 12 x 24 greenhouse with 6′ sidewalls and a 8′ peak height. Your roof panels will be 6′ 6″. This give you slightly less than a 3″ overhang on the roof panels. The profiles come in the following lengths.

H profile (connecting sheets side by side) 12′ or 24′

R profile (ridge profile) 12′ or 24′

U profile (this caps off the channels of the sheets, used on the tops and bottoms of the sheets) 12′

F profile (for corners or flashing) 12′ or 24′

• Roof

I would figure one side and then multiply it by 2.

Each side would have 6 sheets at a 4′ width by 6′ 6″.

When you are figuring the H’s (sheet connectors side by side) you simply subtract 1 from the total number of sheets on each side. So, for this example, you would need 5 H’s at 7′. You would want to order 5 H’s at 12′, as this is the length they are available in. You do not want to use a “patched together” H on your roof (or at any time really).

If you are using a polycarbonate R or ridge, you would need one piece at 24′.

To figure the U’s you would need to figure the linear foot total for the bottom and tops of the sheets. The exception to this is if you are using a ridge. The ridge is already serving the same purpose as the U at the top of the sheet. So, since we are using the ridge we need 24′ of U, or 2 pieces at 12′.

Multiply this by 2 and you are done.

• Side Walls

I would figure one side and then multiply it by 2.

Each side would have 6 sheets at 4′ x 6′.

When you are figuring the H’s (sheet connectors side by side) you simply subtract 1 from the total number of sheets on each side. So, for this example, you would need 5 H’s at 7′. You would want to order 5 H’s at 12′, as this is the length they are available in.

To figure the U’s you would need to figure the linear foot total for the bottom and tops of the sheets. So, for 6 sheets 4′ wide you would need 24′ at the top and 24′ at the bottom for a total of 4 – 12′ U profiles.

Multiply this by 2 and you are done.

I would just go ahead and figure the corners here. You need 4 F profiles at 6′. I would order one 24′ F profile for the entire job.

• Gable ends

I would figure one side and then multiply by 2.

You want to have one sheet the entire length from the ridge to the ground. You will have to cut the angle on site. So, I would order 3 sheets at 4′ x 8′.

When you are figuring the H’s (sheet connectors side by side) you simply subtract 1 from the total number of sheets on each side. So, for this example, you would need 2 H’s at 8′. You would want to order 2 H’s at 12′, as this is the length they are available in.

To figure the U’s you would need to figure the linear foot total for the bottom and tops of the sheets. So, for 3 sheets at 4′ you would need one 12′ U for the bottom. You also need a U for the gables. You know your roof panels are 6′ 6″, so this would be the approximate length of U you would need to cover the gable ends. So, I would order 2 of the 12′ U’s for the gables. This end would need a total of 3 – 12′ U’s. You are going to have a door on one end, and will need to adjust this for the other end. You will want to cut down on your sheets and also be sure to add enough U to frame out your door where you have cut the polycarbonate sheets.

I hope this helps to make the daunting task of figuring a bill of material for your polycarbonate greenhouse easier.