What are the options for replacing a polycarbonate sunroom roof?

Q: About 15 years ago, we had a company install a prefabricated sunroom with tall windows on three sides, supports made of white polycarbonate and a roof of transparent, fluted polycarbonate. Falling tree limbs have punched holes in the outer layer of the roof, and leaf debris has fallen into the channels and cannot be removed. The company that installed the sunroom no longer supplies these roofs, and we haven't been able to find anyone who can replace the roofing. Some firms have said that they could provide reinforced glass but that those panels would be too heavy for the walls to handle.

We’re prepared to replace all the panels, but we don't want to have to replace the entire room. Any suggestions?

D.C.

A: From the picture you sent, it seems as if the roof panels are the type of multiwall polycarbonate used to make greenhouses and other structures. Even if your sunroom roof has a different product, you could probably retrofit it using this material. And if you do need to replace all of the panels to get a uniform look, know that polycarbonate sheets have an expected life span of about 15 to 20 years, so you might have needed to do the work soon, even if tree limbs had not fallen on the panels.

Double-wall polycarbonate is made with square or rectangular channels arranged side by side, with the boxy shapes visible on the panel ends. Erleen Trowbridge, retail supervisor at the Polycarbonate Store, a division of Charley's Greenhouse & Garden (888-977-7659; charleysgh.com), looked at the picture you sent and said she's sure this is the type of material on your sunroom roof.

But she also said she isn't sure the original panels were installed correctly. The channels should run in the direction of the slope, with supports between pieces. But long slopes also need crosswise support at regular intervals. Judging from the picture, the panels on your sunroom were either installed so that the channels run crosswise, or they lack crosswise support.

Trowbridge emailed a Polycarbonate Store handout, "Building with Polycarbonate 101," that discusses the support structure needed when the panels are used for siding and roofing. It lists wood, PVC pipe, aluminum and steel as suitable framing materials. You say the walls have polycarbonate supports, but let's hope that the polycarbonate is just a cover over the joints and that the framing is one of the stiffer materials.

Polycarbonate gets part of its dent resistance (it's bulletproof in the right thickness) from the fact that it flexes when hit by something like a tree branch. Acrylic, which is also a clear plastic, is much stiffer and more brittle, so it's more likely to crack. Because it's flexible, polycarbonate needs to be supported with adequate framing when used as a covering for walls or roofs. According to the handout, roof and wall framing should be spaced no more than 24 inches to 24½ inches from centerline to centerline. And cross blocking between those supports should be installed at least every four to six feet as rafters rise from eave to ridge; walls more than six feet high also need cross supports.

If your roof lacks cross blocking, or if the panels were installed crosswise, have a contractor discuss possible retrofits before you purchase new panels. Suppliers generally can give technical advice, and your local building department can discuss what is needed to support snow loads or high winds.

Once you verify that it would be wise to buy new panels, there are a couple of things to keep in mind. First, although it's relatively easy to cut panels with a fine-tooth blade on a circular saw or table saw, and to join panels side to side, you don't want any seams crosswise as the panels go down the roof. Home Depot sells 24-by-96-inch multiwall polycarbonate panels that are a little over ¼ inch thick for $44.98.

At a specialty store, you’ll find longer, wider pieces, as well as designs that are thicker, that insulate better or that result in a clearer roof. The Polycarbonate Store, which ships nationwide, stocks four-foot-wide panels in different thicknesses and in lengths of eight, 10 and 12 feet. (It can also special-order pieces as long as 24 feet.) Prices start at $65.60 for panels that are similar to what Home Depot sells but twice as wide, and go up to $225.60 for 12-foot pieces of Super 5X-Wall, which has cross-bracing within the channels for added strength where snow and wind are big concerns.

For a situation like yours, 16mm TripleWall ($216 for a 12-foot piece) might look best. It is more transparent, because it has wide channels that provide more clear space between side walls, and it insulates well, because it has two layers of those channels, allowing for more trapped air.

You’ll also need an assortment of accessories, including materials to keep bugs and moisture out of the channels, trim pieces to cover places where panels meet side to side, and screws with neoprene washers to hold panels to the framing. Specialty suppliers offer a wide array of these.

You can find numerous suppliers of multiwall polycarbonate online. In the D.C. area, one option is the Jessup, Md., branch of Polymershapes (301-604-3623; polymershapes.com), which has various locations.

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