Roof flashing is an effective way to keep water from seeping through vulnerable areas in your roof. For example, roof flashing can be used where two or more planes of a roof meet, where a roof meets a wall, or along the roof’s edges. It can also be used around skylights, dormers, vents, as well as your chimney.
It’s important to inspect your roof flashing for cracks and other damage at least once a year. And while most minor repairs can be made by applying plastic roofing cement to damaged areas, some damage will be so extensive that you’ll need to conduct a full replacement. You can usually tell when it’s time to replace your roof flashing if you notice water damage on the ceiling around your chimney, etc. or if the flashing itself has completely rusted over.
Gather Your Materials
Replacing and installing chimney flashing is an advanced DIY job, so make sure you have all the necessary materials.
- Safety: Make sure you have a study ladder, roof brackets, goggles, as well as a safety harness in case you slip or fall while working on your roof.
- Tools: The required tools range from the basic (hammer, chisel, level, tape measurer, and a square) to the complex (straight-cutting tin snips, mortar bit and grinder, and a circular saw).
- Materials: For chimney flashing, you’ll need metal flashing, as this tends to be more durable than the plastic variety. You’ll also need roofing caulk, an ice/water barrier, as well as some self-expanding anchors to hold everything in place.
Remove the Old Flashing
Before you remove the old flashing, you’ll need to carefully remove any surrounding shingles that have been installed over the flashing. Take care not to damage the old flashing, as you can use it as a template for cutting out your new pieces.
- Carefully chip out the mortar joints holding the cap (or upright) flashing in place.
- Chisel the joints even further, and then pry free the base flashing.
- Scrape away any excess roofing cement to achieve as clean and flat a surface as possible.
Install the Ice/Water Membrane
Before laying down the base flashing, seal the base of the chimney with 12-inch wide strips of ice/water barrier. The top of this protective membrane should start four inches from the bottom of the chimney on all sides, and fit tightly around the base to prevent water from seeping in. You’ll then want to run a 36-inch wide piece of barrier behind the chimney until it extends about eight inches up the back of the chimney. This will prevent water runoff from the top of your roof from seeping in.
If you have a brick and mortar chimney, you’ll want to use a grinder to carve out about an inch of mortar where the top of your flashing is going to be. This will allow you to bend the top edge of your cap flashing into the mortar joints to prevent water from falling in between the metal and brickwork.
As mentioned before, you should be able to use your previous flashing as a template for cutting your new flashing. If you don’t have all the metal-working tools you need for this job, you can also order your flashing in precut, pre-bent pieces.
- Base Flashing: This goes on the downhill side of your chimney, and is meant to direct water down to your gutters. Base flashing should be about four inches wider than your chimney on either side, as this will allow you to bend part of it around the front two corners. Secure these corners with caulk, and nail the front of the flashing down with four or five galvanized roofing nails.
- Step Flashing: Step flashing usually come is square pieces that run along the slope of your roof on either side of your chimney. These should fit snugly against one another, and should ? from the downhill end of the chimney up in almost a shingling pattern. Nail a shingle over the bottom of each piece of step flashing before moving on to the next piece.
- Saddle: The saddle is installed on the backside (closest to the peak of your roof) of the chimney and is designed to direct rain water around both sides of the chimney. It should completely cover that 36-inch piece of ice/water barrier mentioned earlier, and be nailed to the roof with some galvanized roofing nails. Install this after the step flashing is in place.
- Cap Flashing: Cap flashing provides an extra barrier of protection by going over the top of your base and step flashing, and saddle. To hold it in place, drill holes through the cap flashing and into the brick, then secure with the plastic anchors. Complete the job by filling in any spaces or open grooves with caulk.
The last step in the flashing replacement process is to install a final piece of ice/water membrane over the flat-laying sections of flashing, then replace the shingles to prevent corrosion. Also, your galvanized metal flashing will last longer with a coat of waterproof paint. Just make sure you clean the metal off first with some lacquer thinner. Replacing your flashing is not an easy job, so if you have trouble at any point be sure to consult a roofing expert.