Roofing
Chimney Leaks: Is It the Flashing or Something Else?
Often, yes. The flashing, where the roof meets the chimney, is one of the most common places a chimney leaks. But it is not the only one. Water can also get in through a cracked crown on top, a missing cap, or porous brick and mortar. A stain on the ceiling or wall right beside the chimney points to the flashing. Water in the fireplace or on the damper points higher up the chimney.
The Chimney Safety Institute of America (CSIA) puts it bluntly: "water causes more damage to masonry chimneys than fire." Late summer is a good time to find the leak, before fall rain and the first fires of the season.
How does chimney flashing work?
A brick chimney and a roof move differently, so the joint between them needs two layers of metal:
- Step flashing (base flashing). Small L-shaped pieces woven in with each course of shingles. One leg lies under the shingle. The other turns up against the brick.
- Counterflashing (cap flashing). Metal set into a mortar joint in the brick and bent down over the step flashing. It sheds water off the brick and onto the step flashing.
Ohio's residential code covers both in Section 905.2.8.1. Base flashing must be corrosion-resistant metal at least 0.019 inch thick, or heavy mineral-surfaced roll roofing. Cap flashing must be corrosion-resistant metal at least 0.019 inch thick. Section 905.2.8.4 adds that chimney flashing "shall be applied in accordance with the asphalt shingle manufacturer's printed instructions."
Wide chimneys need one more piece. Section 903.2.2 requires "a cricket or saddle" on the uphill side "of any chimney or penetration more than 30 inches" wide. A cricket is a small peaked roof behind the chimney. It splits the water and sends it around the sides instead of letting it pool against the brick.
Signs the flashing is the problem
These point toward flashing:
- A stain on the ceiling or wall right next to the chimney.
- Leaks that show up in wind-driven rain from one direction, but not in light rain.
- Tar or caulk smeared along the flashing. Someone has already tried to patch it.
- Counterflashing pulled out of the mortar joint or hanging loose.
- Rusted or bent metal at the base of the chimney.
- Leaves and debris piled behind a wide chimney with no cricket.
- Dark stains on the rafters or decking beside the chimney in the attic.
You can check most of this from the ground with binoculars, or from the attic with a flashlight on a rainy day. Stay off the roof.
What else can make a chimney leak?
| Part | What goes wrong | Where the water shows up |
|---|---|---|
| Crown (the concrete cap on top of the brick) | Cracks, or too little overhang | Inside the chimney, the fireplace, or the walls around it |
| Chimney cap (the cover over the flue) | Missing or damaged | Inside the flue and firebox, rust on the damper |
| Brick and mortar | Worn joints and spalling brick soak up water | Damp brick inside, stains on walls near the chimney |
| Flashing | Failed, patched, or installed wrong | Ceiling and walls beside the chimney, attic framing |
CSIA's recommendations explain each part. It says "a well-designed cap will keep out rainwater." It says crowns "should project beyond all sides by two inches" to protect the brick and mortar below. And it notes that "common brick is like a sponge, absorbing water and wicking moisture to the chimney interior."
Many older homes in Cincinnati's inner-ring neighborhoods still have their original brick chimneys. Old mortar wears out, so leaks there often have more than one cause.
Crown, cap, and masonry work is usually a job for a chimney or masonry contractor. If water is showing up inside the firebox, have a CSIA-certified chimney sweep inspect the top of the chimney and the flue. If the stains are on the ceiling beside the chimney, start with a roofer.
How is chimney flashing repaired?
A proper flashing repair is more than a new bead of sealant. When we redo chimney flashing, the work usually looks like this:
- Remove the shingles around the chimney.
- Add leak barrier on the deck at the base of the chimney.
- Install new step flashing, one piece per shingle course, woven in as the shingles go back down.
- Cut a groove into a mortar joint and set new counterflashing into it, then seal the joint.
- Add a cricket if the chimney is wide enough to need one, or if water and debris collect behind it.
Roof cement over old flashing can slow a leak for a while. It dries, cracks, and traps water when it fails. Treat it as a stopgap until the real repair.
The best time to redo chimney flashing is during a roof replacement. Ohio's code says that when a roof is redone, "flashings shall be reconstructed in accordance with approved manufacturer's installation instructions." If an estimate for a new roof reuses the old chimney flashing, ask why.
Can ice dams cause a chimney leak?
Yes. Snow piles up behind a chimney the same way debris does. Melt water can back up under the shingles and past the step flashing. A cricket helps. So does a leak barrier at the base of the chimney. Our guide to ice dams in Cincinnati explains why they form.
Will insurance cover a chimney leak?
It depends on the cause. A chimney damaged by wind, a fallen tree, or lightning is a different matter from flashing that wore out over years. Insurers generally do not pay for normal wear. Our guide to roof leak water damage and insurance in Ohio explains how insurers look at leaks. Your insurer decides coverage.
How Shamrock can help
We repair roofs and roof flashing, and we restore the water damage a leak leaves inside. We will tell you whether the leak is the flashing or something higher up the chimney that needs a mason or sweep. Request a free roof inspection or learn more about our roofing services. If the ceiling or walls are wet, see our water damage restoration page.
FAQ
How long should chimney flashing last? Metal flashing installed correctly often lasts as long as an asphalt roof. Caulk and roof cement patches last far less. That is why flashing is usually replaced with the roof.
Can chimney flashing be repaired without a new roof? Yes. The shingles around the chimney are removed and replaced as part of the job. On an older roof, matching those shingles can be a challenge.
My chimney leaks only when it rains hard from the west. Why? Wind-driven rain hits one side of the chimney and can push water past a weak spot. That points to the flashing or brick on that side.
Do I need a cricket behind my chimney? Ohio's code requires one on the uphill side of a chimney more than 30 inches wide. On a narrower chimney, it can still help if debris or snow collects there.