Sealing siding around a chimney

Question

I have water coming in from around my chimney. The roofers didn’t finish it, unfortunately I just bought the house so I need to fix it myself. What’s the easiest and best solution to sealing off the top of the siding around my chimney? Pictures are attached. Thanks.

Answer 1

You need to install aluminum or copper flashing all around chimney perimeter that would overlap vertically down from the top of the siding by at least 5–10 inches down.

You would need to grind out a thin continuous horizontal channel 1-1.5 inches deep in the mortar seam directly above where the siding top terminates. Get a roll of aluminum flashing and unroll enough + a foot or so extra to go around entire chimney perimeter.

You’d then create a slightly more than 90 degree bend along the entire length of the flashing (it will look like a upside down “L” shape. You can use a long board and a rubber mallet to do this. The little horizontal part of the L will tuck into the channel and the long vertical part of the L will extend over and down the siding. At the corners of the chimney, you will make a vertical snip across the part of the “L” that tucks into channel so that the long part will be able to bend 90 degrees and wrap around the corners. At the end, you want to overlap the end of the flashing onto where you started by at least 6 inches. Put some tripolymer sealer underneath and secure seam with either rivets or small self-tapping downspout screws. You’d then fill in the channel in with mortar.

This is the crude way of doing it if you don’t have access to a metal hand break. If you can get access to one, you can create fancier shaped flashing that will have a little kick-out at the bottom to allow the water to roll off at the bottom easier.