Preparing the Roof

• Secure any old shingles and check for rotted decking beneath the existing shingles. If your old roof leaked, you may have water damage on the wooden decking under your old shingles. Replace any rotted wood by removing only the shingles in the area that needs replacing. When replacing plywood, make sure the new plywood is the same thickness as the old--the new metal will sag or rise in the area of repair if it is uneven. Replace the shingles: Use felt paper or even the old shingles to build the area up to the same thickness as the rest of the shingled roof; make sure that you secure the material with roofing nails or felt nails. The purpose is only to provide an even surface for laying the metal on; don't worry about mismatched shingles or felt paper--the metal will cover.
  
  

Layout

• Depending on the width of your metal--usually 42 inches wide--snap chalk lines from the bottom overhang and up to the top of the roof ridge. Work from the right to the left of the roof, and remember that the metal will overlap each prior piece by one to two inches, so subtract that amount when calculating the amount of metal you will need. You will only need one line on each side of the roof ridge to begin the first sheets of metal; the following sheets will overlap and snap over the previous metal edge.
  
  

Installation

• Install the first sheet of metal directly over the shingles of the existing roof. Attach the metal with color-matching metal screws--provided by the metal supplier; the screws may need to be a bit longer to allow for the thickness of the old shingles. Make sure the screws are attached securely into the wood beneath the metal and not into the shingles only. Apply a ridge cap over the ridge of the roof after all metal has been attached, and make sure the shingles are all covered. If there are any shingles hanging over the roof edges beneath the metal installation, trim the shingles off using a razor knife.