- 1). Pre-drill holes on every fourth rise of corrugation on both the upper and lower edges of the plastic roofing sheets. Polycarbonate roofing expands and contracts with the heat, so use a drill bit slightly larger than the girth of the fastener. Drill the holes 1 inch from the end of the sheet.
- 2). Screw the first panel into place. Run a generous bead of caulk down the side of the first piece of plastic and along the side of the next piece of plastic. Overlap the edges and screw the second panel into place. The caulk will form a weatherproof seal.
- 3). Continue caulking and screwing in sheets of plastic until the roof is covered. If cutting the plastic is necessary, use a jigsaw with a fine-toothed blade.
- 4). Add flashing if the plastic roof adjoins another part of the roof with a different finish. Flashing covers the seam between the two surfaces and prevents water from flowing down the walls or collecting on the roof. Use tin snips to cut a length of flashing to size. Apply roofing adhesive to the underside and press it into place.
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