Chimney Flashing Repair

Counter flashing pulled out of the mortar joint. The single most common chimney leak we see. Original counter flashing wasn't properly cut into the mortar joint, or has worked loose over decades of thermal cycling. Water runs down the upper chimney face, gets behind the step flashing, into the attic.

Caulk-and-pray, no real counter flashing. Common on chimneys flashed by general contractors instead of roofers. A bead of silicone or roofing tar between the step flashing and chimney face — no counter flashing at all. Fails in 5-7 years. The fix is real counter flashing cut into the mortar joint.

Missing cricket on a wide chimney. NJ Uniform Construction Code (and IRC R1003.20) requires a cricket (saddle) behind any chimney 30 inches wide or wider, measured perpendicular to the slope. The cricket is a small ridge behind the chimney that splits incoming water around the chimney rather than letting it pile up against the upper face. Many NJ chimneys over 30" wide don't have crickets — fixing that alone solves chronic chimney leaks.

Step flashing failure. Step flashing is a series of small L-shaped flashing pieces, one per shingle course, woven into the shingle field as the roof comes up the side of the chimney. When original installs used too-small step flashing (less than 5"×7"×5" minimum), galvanized that has corroded through (25-30 year typical life), or didn't weave properly with each course, water finds its way behind. The fix is full step flashing rebuild with aluminum (doesn't rust) or copper (lifetime) pieces.

Step flashing (under the shingles). 5"×7"×5" aluminum or copper L-shaped pieces, one per shingle course on each side of the chimney. Each step lap overlaps the one below it by at least 2 inches. Step flashing is hidden under the shingles — its only visible portion is the small upturned edge against the chimney.

Counter flashing (over the step, cut into the chimney). Counter flashing is a separate piece that laps over the upturned edge of the step flashing and tucks into a horizontal cut (kerf) in the chimney's mortar joint. We use a wet saw or grinder to cut the kerf — typically 1" deep into the mortar joint, never into the brick face. Counter flashing slides into the kerf, then the kerf is sealed with mortar repair compound or polyurethane sealant (Sika 1A).

Why two parts. The step flashing handles the shingle-to-chimney transition; the counter flashing handles the chimney-face-to-step transition. Together they shed water without relying on caulk or sealant as the primary water barrier. Counter flashing can be removed and replaced if it ever needs service — without disturbing the underlying step flashing or shingles.

Material options. Aluminum is the default — corrosion-resistant, lasts indefinitely, costs less than copper. Lead is the historic option, used for 200+ years and outlasts every alternative — common on slate, copper-roof, and historic-district installs. Copper is the premium option for landmark and high-end residential — develops a protective patina and lasts longer than the surrounding shingle system. We use aluminum for ~80% of NJ residential chimney flashing rebuilds.

Code threshold. NJ Uniform Construction Code references IRC R1003.20: any chimney 30 inches wide or wider (measured perpendicular to the roof slope) requires a cricket. Most NJ residential chimneys over 30" wide are missing crickets — common deficit we find on free inspections.

Cricket geometry. The cricket is a small ridge framed behind the chimney that rises to a peak at the chimney's upper face. Water from the upper roof slope splits around the cricket rather than piling up against the chimney face. Cricket height typically matches the chimney width (e.g., 36" wide chimney = ~12" high cricket peak).

Cricket framing. Built from dimensional lumber (2×4 or 2×6) covered with plywood deck, then waterproofed with ice & water shield (full coverage on every cricket — code requires it under R905.1.2 around penetrations), then shingled to match the surrounding roof field.

Cricket flashing. Where the cricket meets the chimney, full step flashing and counter flashing as on the chimney sides. Where the cricket meets the surrounding shingle field, valley-style flashing.

Retrofit vs new-build. New-build crickets are framed before the surrounding shingle field goes on; retrofit crickets are added by lifting the existing shingles around the chimney, framing the cricket, and re-integrating with the field. Retrofit cost is meaningfully higher than new-build but solves chronic chimney leaks definitively.