How to Repair Chimney Flashing

a person repairing a chimney
  • 4-5 hours
  • Intermediate
  • 300-1,000
What You'll Need
Pry bar
Replacement flashing
Replacement shingles
Nails (specific for roof flashing)
Water-and-ice barrier
Drive-in expanding anchors
Polyurethane caulk

It is challenging to repair chimney flashing, but by doing it without the help of roofers, a lot of money can be saved. Chimney flashing is usually found under the shingles at a 90-degree angle. It is attached to one side of the chimney and one side on the roof. The only way to repair flashing is to replace it.

Before going up on the roof to do the replacement, it is recommended that measurements are taken around the chimney so that the flashing can be ordered. A sheet metal shop that specializes in roofing can make the replacement. If a metal ship will not be used, then measurements, cutting, and bending of the sheet metal must be done before installation. It is extremely important in doing this without professional guidance, to have an exact fit around the chimney and layer correctly to ensure a seal against water. If the flashing is not replaced when needed or installed incorrectly, leaks enter the home which causes damage to the roof deck and eventually to the home.

Step 1 - Remove Shingles and Flashing

Begin by removing the shingles which are around the chimney. Shingles can be removed as far down the roof as needed. Since they are getting replaced, it’s a great time to replace any missing ones. Next, take the hammer and pry bar and remove the old flashing and tar. Since flashing is metal, be careful when removing it.

Step 2 - Replace Shingles

Make sure to thoroughly clean up all the dirt and debris found. Next, shingle from the bottom up to the chimney with new shingles. Use the water-and-ice barrier to seal it.

Step 3 - Install Base Flashing

The base flashing is installed beginning across the bottom of the chimney and on top of the shingles. Take pieces of step flashing to seal the sides of the chimney under each individual shingle. It is important to overlap each piece of flashing over the one before it. This ensures that water is redirected over the top of the shingles. Nail the flashing to the roof’s edge about 6 inches away from each other.

Step 4 - Install Front Flashing

Take the front cap flashing and bend it around the front corners of the chimney. This flashing can be pre-ordered to fit when measurements are taken in advance. If not, the flashing will have to be cut 8 inches longer than the width of the chimney. Nail it in as well.

Step 5 - Install Side Flashing and Cap Flashing

The side cap flashing must overlap each lower flashing. Use drive-in expanding anchors to fasten the flashing. Take a piece of the cap flashing, bend it to fit around the corner of the chimney and secure it to the back of the chimney.

Step 6 - Seal the Cap Flashing

Use polyurethane caulk to caulk along the mortar joint in order to seal the cap flashing. Now, the chimney has proper flashing preventing more leaks. Water can do massive damage to a home, but not anymore.