How to Flash a Chimney on the Edge of a Roof

Because chimneys are usually not actually attached to the house, the seam between the chimney and the point at which the chimney meets the roof presents the risk of water leaks. To compound the problem, homes tend to shift slightly over time, and this shifting can enlarge this seam. To prevent leaks, metal pieces called "step flashing" are used to cover the seam. The process of installing new flashing is generally not as difficult as it may first appear, but you should always exercise caution when working on the roof.

Pry bar
Tin snips
Roofing cement
Roofing nails
Hammer

Instructions

- 1
  Bend the counterflashing pieces upward carefully, followed by the roofing shingles covering the base of the chimney to access the step flashing. The counterflashing pieces, sometimes called cap flashing, are the metal flaps embedded into the chimney mortar that cover the top of the step flashing.
- 2
  Remove the old step flashing from the roof. Pry the roofing nails out of the flashing with a pry bar, then gently pry the flashing off the roof. It is important to try to maintain the shape of the flashing, as it can be used as a template when cutting the new step flashing piece.
- 3
  Cut the new flashing piece with tin snips using the old flashing piece as a replacement.
- 4
  Apply roofing cement to the underside of the flashing piece.
- 5
  Position the new flashing piece against the chimney, and drive a single roofing nail through each end of the flashing and into the roof deck with a hammer.
- 6
  Bend the counterflashing pieces over the new flashing.
- 7
  Apply roofing cement to the bottom of the shingles that cover the flashing, and lower the shingles onto the flashing.

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