How to Install a Polycarbonate Twin Wall

Peel back a bit of the protective film on either side of the polycarbonate, revealing about an inch of the sheet edge at top and bottom. Do not completely remove the films yet; they protect the polycarbonate surface from damage and indicate the side designed to face outward.

Clean any dirt or residue from inside the flutes, which are the vertical compartments inside the sheeting. Brush with a soft cloth, blow them out with compressed air, or insert a vacuum cleaner tool to suck the matter away.

Peel the backing from a length of polycarbonate vent tape. Apply the tape to the bottom of the twin wall sheet, folding it over the edge and sealing to the polycarbonate sides. Ensure the polycarbonate film marked "UV side out" faces outward before applying the tape to prevent accidentally taping the top or flipping the sheet and leaving the wrong side exposed to the sun. The tape, applied properly, seals the polycarbonate interior, allowing moisture to exit but blocking debris.

Apply aluminum tape to the top of the twin wall, folding it over the edges and sealing. This tape is water impermeable, so it blocks the polycarbonate from moisture and debris.

Run strips of foam or the manufacturer's anti-noise tape across the framework wherever the polycarbonate twin wall rests. The tape prevents noise created from the polycarbonate sheeting's expansion and contraction in response to temperature changes.

Align each polycarbonate sheet in place within the framework. Check that the UV side faces out, with the vent tape down and the solid tape up. Any ridges on corrugated polycarbonate or interior walls will run vertically. Attach with the same technique as was used with the previous glazing. Alternatively, install the first H-trim piece for new glazing framework before placing the polycarbonate in place.

Drill two weep holes 1/16 inch in diameter in the bottom of the H-trim. Center over the stud, rafter or other framework with the grooved side facing up. Attach with screws every 12 inches.

Slide the polycarbonate twin wall into the edge of the H-trim. Use a rubber gasket, spread over the sheet edge, if specified by the manufacturer. In either case the fit will be snug; tap firmly but gently with a rubber mallet to encourage the sheet to enter the trim. Rubbing the edges with a bar of soap also helps slide the twin wall in place.

Secure the twin wall to the framing members beneath, using screws fit with neoprene washers. First, drill the hole for each screw, spacing them every 6 to 8 inches around the perimeter and 12 to 16 inches on the interior. Use the next-size-larger drill bit to create a slightly oversize hole, which allows expansion and contraction around the screw later. Avoid inserting screws closer than 1½ inches from the edges.

Drill weep holes in the next and each successive H-trim piece. Slide the trim onto the twin wall's free edge, like putting the top bun on a burger. Don't create tight connections when trimming the sheets; leave about a 1/4-inch gap between the polycarbonate and the H-trim to allow expansion. Secure this sheet as previously performed and repeat across the installation until each piece is installed.

Cut sheets as necessary to fit. Use the saw of your choice, but ensure that the blade is sharp. Clamp the material tightly to avoid vibrations that may cause a poor cut or damage to the cut edge. Avoid cutting slowly or too quickly, which will melt or tear the polycarbonate.

Apply cap trim, sometimes called U-trim or J-trim, to the tops and bottoms of each polycarbonate sheet. Drill weep holes 1/8 inch in diameter every foot across the length of the trim. Secure with screws according to the manufacturer's instructions.

Caulk between panels and over screw heads to encourage a watertight installation. Remove the film covering the polycarbonate twin wall once construction is complete.