Chimney Flashing: The Most Common Roof Leak Source

If you have a chimney and a roof leak, there's a better-than-even chance the chimney flashing is the culprit. Chimney flashing is one of the most complex details in residential roofing, and it's also one of the most frequently improperly installed or maintained components on Massachusetts and Rhode Island homes.

Why Chimneys Are Such a Common Leak Source

Chimneys penetrate the roof at a complex intersection: masonry (brick or stone) meets wood framing, both expanding and contracting at different rates with temperature changes. Add to this:

• •The chimney interrupts water flow from the upper roof, requiring careful diversion
• •The joint between masonry and roofing is one of the most stressed transitions in the roofing system
• •Many Massachusetts homes have chimneys that were improperly flashed with tar rather than proper sheet metal
• •Freeze-thaw cycling stresses every chimney flashing joint repeatedly each winter

The result: chimney flashing maintenance and repair is one of the most common service calls Roofing Doctors handles across Massachusetts and Rhode Island.

The Components of Proper Chimney Flashing

A properly waterproofed chimney requires multiple interlocking components:

Base Flashing

L-shaped metal pieces installed at the base of each chimney face, running up the chimney sides and under the shingles. The base flashing handles the roof-to-chimney transition on the sloped roof surface.

Counter Flashing (Step Flashing for Sides)

Metal that is cut into the chimney masonry (embedded in the mortar joints) and laps over the top of the base flashing. The counter flashing is attached to the chimney - so it moves with the chimney rather than with the roof framing. This two-piece system (base flashing + counter flashing) accommodates the differential movement between chimney and roof.

Front Apron Flashing

A flat piece of metal at the downslope face of the chimney (the face facing the eave). This diverts water around and away from the chimney base.

Chimney Cricket (Saddle)

For chimneys wider than 30 inches (measured perpendicular to the ridge), building codes require a "cricket" - a small peaked structure built on the upslope side of the chimney. This prevents water and debris from accumulating behind the chimney, which would otherwise create a dam that backs water against the chimney-roof intersection.

A chimney without a required cricket is a chronic maintenance problem and a building code violation on newer construction.

The Tar Patch Problem

Many Massachusetts and Rhode Island homes, particularly those built before 1980, have chimney flashings that were sealed with roofing tar or hydraulic cement rather than proper sheet metal flashing. This is sometimes called "sloppy flashing" and it's an extremely common finding on older homes.

Tar-based patches seem to work initially but fail within a few years as the tar becomes brittle, cracks with temperature cycling, and is pushed apart by the freeze-thaw-driven movement of the chimney. The result: the same chimney keeps leaking, repeatedly patched, without addressing the underlying problem.

**The permanent fix:** Remove the shingles around the chimney, remove all tar-based materials, and install proper base flashing and counter flashing. This is more work than a patch, but it provides 20-30 years of reliable service rather than 2-3 years.

Signs of Chimney Flashing Problems

**Interior signs:**

• •Water staining on the ceiling adjacent to or below the chimney
• •Dark staining on the chimney breast (interior masonry face)
• •Musty smell near the fireplace
• •Peeling wallpaper or paint near the fireplace

**Exterior signs:**

• •Visible tar or black sealant applied heavily around the chimney base (indicates previous patch attempts)
• •Rust staining at the chimney base
• •Counter flashing that is visibly separated from the chimney masonry
• •No chimney cricket visible on a wide chimney
• •Damaged or missing mortar joints at the chimney (where counter flashing is embedded)

Chimney Flashing Repair vs. Replacement

**Repair** (counter flashing reglazing/re-bedding):

If the metal flashings are sound but the mortar that embeds the counter flashing has failed, the counter flashing can be re-embedded with appropriate sealant without full replacement. Cost: $400-$800.

**Replacement** (full chimney reflashing):

When the metal flashing itself is corroded, improperly installed, or tar-based rather than true metal, full replacement is required. Cost: $800-$2,000+ depending on chimney size and complexity.

When done in conjunction with a full roof replacement, the incremental cost of proper chimney reflashing is modest since the surrounding shingles are already being removed.

Roofing Doctors provides chimney flashing inspection, repair, and replacement services across Massachusetts and Rhode Island. We photograph every chimney we work on and provide written documentation of findings and the work performed.