Which Polycarbonate Panel Do You Need? A Buyer's Guide by Project

"I need polycarbonate." That is how most calls start. Then comes the pause, because the next question is the hard one: which sheet, what color, how many of them.

Here are the answers, sorted by what you are actually building. We stock one thing, 8 mm twin wall in clear, bronze and opal, so everything below comes from that and from what we watch go up around Seattle.

Two numbers decide almost everything

Thickness. Eight millimeter twin wall is the size that fits most backyard jobs. It spans 2 to 3 ft between rafters. A 4x8 sheet weighs about 10 lb, so you are not calling a neighbor over to help lift it. The air gap between the two walls puts it around R-1.74, where single pane glass limps in at R-0.9.

Six millimeter is not a mistake on a short greenhouse span, and it costs less. It just gets floppier with age. Ten and sixteen millimeter are commercial sizes. On a patio roof you would be paying for weight you will never need.

Color. This is where people go wrong, and it is an expensive thing to get wrong.

Clear passes 76% of the light. Excellent over a greenhouse. Less excellent over the chair you wanted to sit in.

Bronze passes 25%, and that is the entire point of it.

Opal sits at 44% and scatters the light instead of letting it through in a beam, so nothing underneath ends up cooking in a hot spot.

Pergola or patio cover

Bronze. Nearly always bronze.

People build a pergola to sit under it. Put clear on top and you have built a greenhouse with chairs in it. Clear earns its place only when the pergola is decoration, or it faces north and never really catches the sun.

Measure from the house to the outer beam. A 4x12 covers a 12 ft run in one piece, no cross seam, and cross seams are where roofs start leaking three winters later. Sixteen foot run, take the 4x16.

Use snap profiles rather than H. You will be looking at the underside of this roof every summer evening, and the snap cap hides the screw heads.

Counting is simple: width in feet, divided by four, rounded up. One profile per seam, one more for each outer edge. A 50 pack of screws does three or four sheets.

Greenhouse

Sheet: opal if you grow through the summer, clear for a cold frame or a winter house where light is the thing you are short of.

Size: greenhouse roofs are short. The 4x8 and 4x12 do nearly all of it, and the walls come out of the same sheets.

Joints: H profiles. Cheaper than snap, they lie flat, and nobody has ever stood admiring a greenhouse ceiling. Leave a 1.5 in gap, slide the H in, screw every 2 ft.

Thinking of an arch? These sheets cold bend. No heat gun, no tricks. But 55 in is the tightest radius 8 mm will take, which works out to an arch roughly 9 ft 2 in across. Go tighter and it cracks along the flutes. Not that day, though. A few weeks later, once you have stopped thinking about it. Flutes run along the curve, never across it.

Then there is the thing almost everyone skips: vented tape on the bottom edge. Twin wall breathes. Leave the tape off and by next spring the flutes are full of condensation and turning green from the inside. Aluminum tape goes on the top edge, to keep water and dirt out.

Carport

Bronze. A car parked under clear polycarbonate in August is an oven with a steering wheel.

Carports are wide and shallow, so 4x8 or 4x12 across, as many as the width takes. If the roof is one long slope, a 4x16 or 4x20 runs it in a single piece. Snap profiles are fine here. On a long open span that catches wind, the aluminum sealing bars are stiffer and worth the difference.

Deck or balcony roof against the house

Clear if there is a window behind it and you want the room to stay bright. Bronze if the deck wins the argument.

The run is wall to outer edge, usually 8 to 12 ft on a deck.

Whatever you build, give it fall. An inch per foot is the minimum. Flat roofs hold water, and by the second winter you can see the outline of every puddle that ever sat there.

Shed or workshop skylight

One opal 4x8, cut to the opening. Daylight without a glare bar lying across your bench at four in the afternoon. There are no joints to think about: U channel caps on the cut edges, a bead of silicone where it meets the frame.

A real order, worked out

Patio cover, 12 ft deep by 16 ft wide, bronze, snap profiles:

• 16 ft of width means four sheets of 4x12 bronze
• three seams plus two outer edges means five snap profiles at 12 ft
• about 15 screws a sheet, call it 60, so two packs of 50
• one roll of aluminum tape and one of vented, and you will have some left over

What we do not sell, and why

Corrugated single skin is cheaper per sheet. It also drums in the rain loud enough to hear from indoors. It sags between purlins. And with no air gap in it, it insulates nothing at all.

Solid polycarbonate really is stronger than twin wall. It is also heavier and more expensive, and it has no air gap either, which is what makes it right for security glazing and wrong for a roof.

Acrylic is the one that catches people out. On the shelf it looks identical. Then hail arrives, or it cracks around a screw hole, and the difference becomes obvious. Polycarbonate takes the dent and carries on.

So we stock one product, because it is the one that suits every job above.

Still working it out

Send us the width and depth of what you are covering, and what it is for. Same day you get back a sheet count, a profile count and the delivery price for your ZIP. Call or text (702) 351-2441.