How to install a chimney flashing

The chimney flashing is installed to prevent leaks from entering the gap between the chimney and roof. You can avoid any costly repairs of the roof and ceiling by simply installing a flashing.

Protective gear is very important when working on the roof.

A safety harness, protective gloves and glasses are very important items to have. Also, an assistant is recommended.

Tools and materials needed

  • 8 inch galvanized flashing
  • Pre-bent Galvanized step flashing
  • Tin snips
  • Protective gloves
  • Hammer
  • Flat bar
  • Roof shingles
  • Roofing nails
  • Silicone caulk
  • Caulk gun
  1. Start by measuring the width of the chimney. Cut a piece of galvanized flashing 10 inches longer than the chimney width. Use tin snips to do so. The starter strip of the flashing must be positioned at the front of the chimney. Bend the flashing horizontally and make sure it follows the roof angle.
  2. Cut 5 inches off the edges of each side of the flashing. Make sure not to cut more than halfway from the top to the bend of the chimney flashing. Keep the bottom piece of the flashing intact so that the flashing can remain flat against the roof.
  3. Put the starter strip of the flashing along the chimney edge and bend them in place. Carefully nail the flashing into the chimney masonry and not to the roof itself.
  4. Mount the step flashing on the roof. Bend and set them using an overlapping pattern. Place a shingle then step flashing then a shingle and repeat the process. The flashing shouldn’t be visible once installed.
  5. The top flashing must be installed as the starter strip, only this time, you have to cut halfway from the flashing top to the bottom. Position and nail the flashing is in place. Don’t nail it into the roof.
  6. Silicone caulk needs to be applied as an adhesive at the edges of the shingles. Any exposed piece of the flashing must be covered with silicone caulk.
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