How to Replace Metal Chimney Flashing

When a water trickle from your ceiling fills all your kitchen pans and you've added the dog's bowl to help catch the water, it's time to think about replacing that leaky metal flashing around your chimney. What might first appear to be a daunting project can be accomplished in a few hours time once you know the process.

Difficulty: Moderately Challenging

Instructions

Things You'll Need:

• Hammer
• Flat bar
• 8-inch galvanized flashing
• Pre-bent galvanized step flashing
• Roofing nails
• 100% silicone caulking

Remove Old Flashing

1. Peel back the existing shingles at least 18 inches away from the base of the chimney, but do not remove them. Do this carefully using the flat bar and hammer to gently loosen the adhesive. Remove the old roofing nails.

2. Remove the old flashing and discard it, making sure to pull all old nails out of the chimney to provide a smooth surface for the new flashing.

3. Scrape all old roofing cement from the area where the new flashing will be installed.

Install New Flashing

4. Cut a length of the galvanized flashing 10 inches longer than the width of the chimney. This is the starter strip. Beginning at the front edge of the chimney, on the lowest side, bend the flashing horizontally at the same angle that the roof meets the chimney. The bend should be in the middle and run from side to side.

5. Cut the flashing on both sides exactly five inches from each edge. Cut only halfway down from the top to the bend line. Leave the bottom portion of the flashing intact so it lies flat against the roof.

6. Place the starter strip along the edge of the chimney and bend the cut sides down to the roof on either side. Do not nail the flashing into the roof; only nail the sides of the flashing into the chimney, smoothing it in place as you go. No nails should ever be placed into the roof, itself.

7. Smooth existing shingles back over the front of the flashing. You will continue to do this as you progress up the sides. Always work from the bottom up to provide a leak-proof barrier.

8. Begin installing the step flashing up the sides of the roof, placing the pre-formed bend along the seam between the roof and the chimney. Use the "step" method of overlapping shingle, then flashing, then shingle, then flashing, all the way up the sides. After each piece of step flashing is installed fold that layer of shingles on top. The next piece of step flashing will be placed, overlapping the shingle just as you would with regular shingles. No flashing should be visible as you replace the shingles. Again, do not nail through the step flashing into the roof, only nail into the chimney.

9. Follow the same procedure you did for the starter strip, when you reach the top edge of the chimney, cutting the galvanized flashing 10 inches longer, bending horizontally and measuring in exactly 5 inches from each edge. This time you will be making the edge cut halfway from the bottom instead of the top. Place this piece in the same manner, folding the cut bottom pieces against the roof. Carefully nail only into the chimney and fold the shingles back into place.

10. Squeeze a small amount of silicone caulking just under the edge of the shingles to help seal them down. The heat from the sun will do the rest. Locate the only areas that do not overlap on the new flashing; they are at the vertical corners. Apply the silicone caulking heavily to these areas, making sure no gaps are left. Let dry completely and replace the siding on your chimney.

Tips & Warnings

• Take safety precautions when on a roof. If the grade is steep, attach a tie-off to the ridge following OSHA specifications.