Chimney Flashing

In the dallas area, chimneys are well known for leaks, and the problem is usually the sheet metal flashings. Simply look for water-stained ceilings or other signs of leaks in the vicinity of your chimney.

You'll want to install new chimney flashing if it's missing, rusted, falling out or completely covered with roofing tar. It's also a good time to install new flashing when you put on new shingles because you'll want it to last as long as the new roofing (25 to 40 years).

This procedure is the same for wood shingles. You have to be comfortable with being on the roof. You have to measure, cut and bend sheet metal to fit precisely around the chimney and layer the parts so they shed water. Even so,

In addition to the flashing and shingles, buy a roll of self-adhering roofing membrane (also called ice-and-water barrier), two tubes of polyurethane caulk, and a package of 25 drive-in expanding anchors (optional) from a home center or roofing store.

Besides basic hand tools like a hammer, tape measure, 2-ft. level and square, you'll need a good pair of straight-cutting tin snips, a 3/16-in. masonry bit and a grinder or a circular saw fitted with a drycut diamond blade for grooving the mortar.

You'll need a good ladder that goes over the roof by two feet at least. To do this work properly you need to hire a professional roofer, who has proper safety equipment. Call a Dallas roofing company today.

Once you complete the tear out, shingle to the bottom of the chimney and seal around it with 12-in. wide strips of "ice-and-water barrier". Lap the strips 4 in. up onto the bricks and overlap adjacent strips to shed water. Use 36-in.wide strip across the top of the chimney. Stick this piece to the roof boards and up 8 in. onto the back of the chimney. Start the flashing job by installing the first piece of base flashing across the bottom of the chimney and over the top of the shingles

Seal the sides of the chimney with pre bent pieces of step flashing under the shingles . Slightly flatten the step flashing before you nail it in to ensure a tighter, spring-tensioned fit against the chimney. Pay close attention to overlapping each piece of flashing onto the preceding one in such a way that water is diverted over the top of the shingles. This is the key to a good flashing job.

Complete the base flashing by nailing the saddle to the roof and sealing it with additional strips of membrane. Shingle over the portion of the saddle that rests on the roof and cut the shingles neatly along the valley, leaving 2 in. of metal exposed.

The next step is to mark and cut the grooves in the chimney's mortar joints to accept the cap flashing. Start at the front of the chimney and mark the third mortar joint up from the roof. Extend this mark around both front corners about 6 in. Now mark the mortar joints on the sides of the chimney so the flashing steps up until you reach the back . Depending on the slope of the roof, each step will jump up one or two mortar joints and should lap over the previous piece of flashing at least 4 in. Mark straight across the back of the chimney to cover the saddle

Cutting the groove in the mortar is easiest with a grinder and a diamond blade. A circular saw with an inexpensive abrasive masonry blade will also work. Cut close to the brick on the lower edge of the mortar joint. This way, the final caulk joint will be less visible. Cut the slots about 1 in. deep and 1/8 in. wide. Make them a few inches longer than you think is necessary, keeping in mind that each piece of cap flashing has to overlap the one below it by about 2 in.

The little backward bend on the short leg of the cap flashing acts as a barb to hold the flashing in until you're ready to caulk. If the flashing is still loose, wedge it tight with a small plastic shim. Once all the cap flashings are in place, complete the job by filling the groove with polyurethane caulk.

Your new flashing will last longer with a coat of paint. But don’t paint the bare galvanized metal without cleaning it first with lacquer thinner. Another option is to order the slightly more expensive prepainted metal flashing.

Required Tools

Extension ladder

Grinder

Roof harness

straight cutting tin snips

Diamond blade (dry-cutting), roof brackets

Required Materials

Galvanized step flashing

Galvanized coil stock

26-gauge galvanized sheet steel

Galvanized front base flashing

Self-adhering roofing membrane (ice and water barrier)

Polyurethane caulk

Drive-in expanding anchors (optional)

If you need help with any of this just get in touch with DFW Best Roofing.