Chimney Flashing Repair

Two layers, one seal

A chimney and a roof move independently. The roof deck expands, contracts and settles; the masonry doesn't move with it. Proper flashing handles that with two separate pieces:

• Base and step flashing is tied into the roof. Step flashing is a series of bent pieces woven between the shingle courses up the sides of the chimney, with base pieces at the front and a cricket or saddle on the uphill side of wider chimneys.
• Counterflashing is tied into the chimney. It's set into the mortar joints, or into a cut made in them, and laps down over the step flashing.

Because the counterflashing overlaps the step flashing without being fastened to it, the two can slide past each other as things move, and water still runs down onto the roof.

Why it often fails after a roof replacement

Flashing problems often appear within a season or two of a new roof. Common reasons:

• The old step flashing was reused, or new step flashing wasn't woven in with the shingles
• Counterflashing was bent up and pushed back down, loosening it from the mortar joint
• The counterflashing was only face-nailed or glued to the brick, with no cut into the joints
• A bead of caulk or roofing cement was used as the main seal, and it has dried out and cracked
• No cricket was built behind a wide chimney, so water and debris pile up against it

If you're planning a new roof, read planning the chimney with a roof replacement before the work starts.

Signs of a flashing leak

• Stains on the ceiling or wall right beside the chimney, often worse with wind-driven rain
• Damp or darkened roof sheathing or rafters next to the chimney in the attic
• Flashing you can see lifting, rusting or held on mainly by sealant
• Gaps between the counterflashing and the brick

Brick and mortar above the roof can produce the same stain pattern, because water soaking into the chimney can run down inside it and come out at the roof line. Telling the two apart is the main job of the assessment.

How we assess it

We look at the flashing on all sides from the roof when it's safe to get up there: how the step flashing is laid in, how the counterflashing is attached, the condition of sealants, and whether there's a cricket where one is needed. We also look at the brick and crown above it. In the attic, when it's safe and accessible, we trace where water stains start on the framing.

When it isn't clear whether water is coming through the flashing or through the masonry, a controlled water test, wetting one area at a time, can separate them. You get photos and our findings before any repair is scheduled.

If your roof was replaced recently, it helps to know who did it and when. That information can make a difference if the roofer needs to be involved in the repair.

Repair options

Resealing alone only makes sense when the metal is sound and correctly installed. Sealant that's covering a missing or badly installed piece of flashing will fail again.

Working with your roofer

Flashing sits where two trades meet. Replacing step flashing means working with the shingles beside the chimney, and on some roofs, including slate, tile or metal, or a roof still under a roofer's workmanship coverage, it makes sense for the roofer to be involved. If that's the case, we'll say so in our findings so you can decide who does which part.

What a cricket is and when you need one

A cricket, also called a saddle, is a small peaked structure built on the roof behind the chimney, on the uphill side. It splits water and debris coming down the roof and sends them around the chimney instead of letting them pile up against the back wall.

Without one, the back of a wide chimney becomes a dam. Leaves and snow collect there, water sits against the flashing, and in winter ice can build up and push under the shingles. Building codes and roofing guidance generally call for a cricket behind wider chimneys, and your town's construction office can confirm what applies to your roof. If your chimney is wide and the leak stain is on the uphill side, the back of the chimney is one of the first places we look.

A cricket is framed and covered with roofing or metal, then flashed to the chimney like the rest of the roof. It's often added or rebuilt during a roof replacement.

Limits and what affects the scope

• Roof type and pitch
• Chimney width and whether a cricket is needed
• Condition of the mortar joints the counterflashing sits in
• Whether the masonry is also letting water in, which flashing work won't fix
• Interior damage such as wet drywall or insulation, which is outside chimney work

Next step

If you've got a stain beside the chimney, note when it shows up and whether the roof was recently replaced, and send that with your request. A team member will contact you to confirm a time for the assessment.

Request a flashing assessment

Questions homeowners ask