Installing Chimney Flashing
by Lee Wyatt
(last updated December 17, 2018)
Do you have a draft or even a water leak around your chimney that you simply can't explain? If so, then chances are you have some chimney flashing that needs to be replaced. Chimney flashing is what helps to cover the small gaps that lie between your chimney and your roof. Installing chimney flashing is a fairly easy project, that most people can accomplish in a single weekend. Here's how you do it.
- Pneumatic nailer
- Nail gun
- Circular saw
- Mortar blade
- Claw hammer
- Wire brush
- Tin snips
- Roofing cement
- Caulking gun
- Remove old flashing. Before you begin installing chimney flashing, you need to make sure that you remove your old flashing. Do this by first removing the shingles around the chimney, as well as the flashing underneath it. As you do this, make sure that you are wearing heavy duty work gloves since the metal flashing can often be sharp, and you don't want to get cut.
- Install a cricket. If at all possible, you will want to use the existing cricket for your chimney. A cricket isn't a small bug in this case, but rather an angled structure that helps to direct rain and snow away from the base of the chimney. If you can't use the existing one, make a new one modeled off of your old one.
- Cut some flashing. Use some tin snips cut some flashing that you can use as a base. This base flashing will need to go around your entire chimney, and should be made out of 10 or 12 inch galvanized metal. If at all possible, use the old pieces as a pattern for your new flashing. Bend the flashing, once you have cut it, so that it will cover the chimney as well as the roof, and cut at the corners to allow you to bend the piece of metal around the chimney. Nail the metal towards the roof with only one nail at each edge, and place some roofing cement on top of the nail to hold it in place.
- Cut and install step flashing and counterflashing. Continue to shingle your roof as you normally would. Make sure that you install a little bit of step flashing against the chimney before you place the final shingles against the chimney. This flashing will help protect the shingles from the heat of the chimney, and apply a little bit of roofing cement to help hold the flashing in place against the chimney. Nail the flashing to the roof by using two nails, and a little bit of roofing cement. If at all possible, use the existing mortar grooves in your chimney to help guide the counter flashing. If you can't then use a circular saw and a mortar blade to create a groove that is 1-1/2 inch deep. Use your old counter flashing as a pattern for the new, and allow each piece to overlap the previous by three inches. Bend the top edge of the flashing so that it will go into the mortar groove.
- Install shingles, flashing, step flashing, and counterflashing on the cricket. Repeat steps three and four for the cricket. When finished, shingle your chimney and cricket as you would the rest of your roof.
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