Galvanized roof panels are composed of steel that has been specially coated with zinc to protect it from rust and corrosion. It is a long-lasting material that can be painted for a better appearance than the basic shiny metal. It typically comes in one of two styles: corrugated roofing with alternating ridges and valleys, or standing seam with wide flat areas and structural upright sections. Installation techniques for both styles are similar, but corrugated panels overlap at edge whereas standing seams interlock.
Preparing for Metal Roof Installation
Prepare the roof with "strip sheathing," 1-by-4-inch boards nailed horizontally across roof rafters. These are typically spaced about 24 inches apart, but check local building codes for specific installation. Install filler strips or drip edging on eaves and edges to cover gaps between the sheathing and the metal panels; these metal strips should come with the roofing, shaped to conform to the roof panels. Use galvanized nails with a hammer to install edging and filler strips.
Installing the Galvanized Roof Panels
Install the first galvanized roof panel at one bottom corner. Fasten it with galvanized screws with plastic washer caps by using a screw gun. Place the first screw at the outside bottom edge, add screws at the other edge and the top of the panel to secure it, and finish fastening it with screws about 24 inches apart. Consult specific recommendations of the manufacturer for screw placement. Put screws in flat or valley areas so that they lay tight against the wood sheathing.
Add a second panel. Overlap corrugated roofing panels by one ridge and one valley; secure the second panel with screws through both pieces. Slide the flat edge of a standing seam panel into the slot on the seam of the other panel; standing seams interlock much like tongue-and-groove lumber, with one panel fitting into the other to provide a solid connection without overlapping
Covering the Roof
Cover the bottom of the roof. Start a second row, if necessary, with a half-panel of corrugated steel, cut lengthwise with tin snips or a metal saw, so the vertical joints are not aligned. Start a second row of standing seam with a full panel or according to the manufacturer's recommendations; some will use a half-panel to avoid aligned seams. Overlap panels from top to bottom by at least 6 inches, but check manufacturer's recommendations as overlaps can vary.
Work up the roof on both sides to the peak. Finish the peak with ridge caps, which are made to conform to the roof panels. Overlap joints of the caps at least 1 inch. Work along the peak in the direction of any prevailing wind. Let the overlap cover the screws of the previous cap. Seal the screws on the last cap with clear caulk.