How to Install a Corrugated Metal Roof Flashing


Knowing how to install a flashing on a corrugated-metal roof prevents you from making errors that compromise the water tightness of the roof. You need to flash all roof-transition points to protect against water penetration. Typically, this includes flashing the edges of the roof as well as where two slopes meet at a joint. Corrugated-roofing manufacturers produce preformed flashing for each type of roof transition to facilitate a consistent and functional finish.

Things You'll Need

  • Rake flashing
  • Butyl tape
  • Gasketed roofing screws
  • Valley flashing
  • Inside closures
  • Install rake flashing for the side or gable roof edges. Fasten a length of butyl tape along the top of the downward slope of the first, full corrugation from the roof edge. This prevents rainwater driving under the flashing.

  • Position the rake flashing over the first, full corrugation so that the flashing edge lips downward into the valley between the corrugated ribs. Attach the flashing through the top of the first corrugated rib with a gasketed roofing screw. Use a 1/2-inch longer roofing screw than you did for the corrugated panel installation so that the flashing anchors into the roof deck.

  • Fasten butyl tape, 1/2 inch up from the flashing lip, along the underside of the rake flashing that attaches to the house wall. Attach the flashing to the wall with gasketed screws just above the butyl tape. Screw the rake flashing to the roof and wall at intervals recommended by your flashing manufacturer. Typically, fastening intervals vary from 6 to 24 inches for rake flashing.

  • Attach valley flashing to the corrugated roof where two roofs meet on a downward slope and form a "V" shape. Center the valley flashing over the roof joint. Leave 6 inches to each side of the valley-flashing center completely clear of your roofing panels so that water drains freely along the flashing.

  • Fasten a length of butyl tape, 1-inch inset from the edge, on the underside of the corrugated roofing panel that you need to fit to the valley flashing. Press an inside closure onto the butyl tape to prevent water flowing under the roofing panel. Attach butyl tape along the base of the inside closure.

  • Attach the valley flashing with gasketed screws through the top of a roofing-panel rib that you fitted with the inside closure. Fasten the valley flashing at 6-inch intervals or according to your flashing manufacturer's guidelines.

  • Repeat step 5 and 6 to install the valley flashing to the adjacent slope.

Tips & Warnings

  • Use gasketed roofing screws because the rubber washer serves as a seal against water penetration.
  • Use steel flashing with a galvanized steel roof and aluminum flashing with a Galvalume roof to maintain the longevity of the roofing system.
  • Wear safety goggles, work gloves and long sleeves when installing metal flashing to avoid injury from sharp edges.

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