How to Inspect Chimney Flashing for Leaks in 4 Steps

TL;DR: Chimney flashing—the metal seal where your chimney meets the roof—fails more often than the chimney itself. Look for rust, separation at caulk lines, missing mortar in counter flashing, and water stains on the attic side. Catch these early and a roofer can reflash the joint for $400–$900; ignore them and you're replacing sheathing and framing for $3,000+.

_Last reviewed: July 2026 · 6 min read_

Most chimney leaks don't start in the flue or the crown. They start where metal meets brick and brick meets shingles—the flashing assembly that wraps the base of your chimney. A single rusted seam or a bead of failed caulk can funnel gallons into your attic every storm, rotting roof decks and ceiling joists before you see the first brown stain downstairs.

Okoniq Property Hub logs roof inspections, photos, and repair dates so you can prove regular upkeep when you sell or if an insurance adjuster questions a claim.

What is chimney flashing and why does it fail?

Chimney flashing is a two-part metal system: step flashing (short L-shaped pieces woven into shingle courses along the chimney sides) and counter flashing (metal embedded in mortar joints that overlaps the step flashing to shed water). On the upslope side, a saddle or cricket—a peaked mini-roof—diverts water around the chimney.

Flashing fails for three reasons. Thermal expansion cracks caulk seams within 5–10 years. Mortar holding counter flashing crumbles faster than brick, leaving gaps. And roofers who replace shingles without touching the flashing often disturb its seal, especially if they don't reinstall step flashing under the new shingles. According to the National Roofing Contractors Association, poor flashing accounts for 95% of masonry-chimney roof leaks.

Check flashing every fall before rain season and after any roof work. Combine this with your annual chimney and fireplace inspection before burning season.

How do I inspect step flashing and counter flashing from the roof?

Grab binoculars if you're not comfortable on a ladder; many problems are visible from the ground on a clear day. If you go up, wear soft-sole shoes and only walk when shingles are dry and cool (wet or hot shingles tear).

Walk around the chimney base. Step flashing should lie flat against brick and tuck under each shingle course; you'll see 4–6 inches of metal between the brick and the shingle edge. Look for rust holes, especially at the bottom edge where water pools. Check the caulk bead where metal meets brick—if it's cracked, peeling, or missing, water will wick behind the flashing. Pull gently on a piece of step flashing; if it moves, it's no longer nailed or the nail has rusted through.

Counter flashing sits in a mortar joint and laps over the step flashing by 3–4 inches. Inspect the mortar reglet (the groove the metal sits in). If mortar is sandy, cracked, or missing, counter flashing will pull out in wind or let water run behind it. Press a flat screwdriver gently into the mortar; if it crumbles, the joint needs repointing before you reflash. On the upslope side, check the cricket seams where metal meets metal—these are often sealed with roofing cement that dries out and cracks every 7–10 years.

What should I look for on the attic side?

Climb into the attic with a bright flashlight during or right after a heavy rain. Trace the chimney from the roof deck down. Look for:

• Water stains on the wood framing around the chimney chase (dark streaks, mold, or white mineral deposits).
• Damp insulation within two feet of the chimney base.
• Rust streaks on metal chimney liners or flue pipes.
• Daylight showing through gaps between chimney masonry and the roof deck (a sign flashing was never installed or has pulled away).

If you see active dripping, mark the entry point with painter's tape and measure its position relative to the chimney corners—this tells the roofer exactly where the flashing failed. Compare what you see to attic photos from your last inspection; new stains mean a new leak or an old patch that's failed. Pair this check with a look at your attic ventilation balance to rule out condensation as the moisture source.

When do I repair flashing myself versus call a roofer?

You can handle minor resealing if the metal is intact and the leak is caught early. Clean the joint with a wire brush, let it dry completely, and apply polyurethane or butyl-based flashing sealant (not silicone—it doesn't stick to dirty masonry and fails in UV). Press a continuous bead into the metal-to-brick seam and smooth it with a gloved finger. This buys you 1–3 years if the underlying metal is sound.

Call a roofer if you find rust holes, missing pieces, loose counter flashing, or crumbling mortar. Re-flashing a chimney costs $400–$900 depending on size and roof pitch; it involves pulling back 2–3 shingle courses on each side, installing new step and counter flashing, and embedding the counter flashing in fresh mortar. If the cricket is rotted or missing, add $300–$600 for fabrication and install. Roofers will also replace any soft sheathing they find—rot spreads fast once water gets under shingles.

Never caulk over rust holes or use roofing tar as a long-term fix. Tar dries brittle in 18–24 months and traps moisture underneath, accelerating rot. If water has stained your ceiling, assume you have sheathing damage; check for soft spots by pressing the roof deck from the attic side near the chimney.

How often should I re-inspect and what records should I keep?

Inspect flashing every fall and again in spring if you're in a freeze-thaw climate. Ice dams and snow melt stress flashing seams more than summer rain. After any roof repair—even if the crew says they didn't touch the chimney—go back up and photograph the flashing; roofers sometimes step on it or knock counter flashing loose while working nearby.

Take close-up photos of each side of the chimney, the cricket, and the mortar joints. Note the date, weather in the past week, and any stains or gaps you see. Upload these to Okoniq with a "Chimney flashing – OK" or "Chimney flashing – resealed east corner" note. If you hire a roofer, scan the invoice and attach it to the same maintenance thread. When you sell, this log proves you maintained the roof system and didn't hide active leaks.

FAQ

How long does chimney flashing last before it needs replacement?

Properly installed copper or lead-coated copper flashing can last 50+ years. Aluminum and galvanized steel flashing typically last 20–30 years before rust forces replacement. Caulk and roofing cement seals need renewal every 5–10 years regardless of metal type.

Can I use silicone caulk to seal chimney flashing?

No—silicone doesn't adhere well to masonry or painted metal, especially if the surface is dusty or damp. Use polyurethane or butyl-based flashing sealant labeled for metal-to-masonry joints; it stays flexible in temperature swings and bonds to dirty surfaces better than silicone.

What is a chimney cricket and do I need one?

A cricket (or saddle) is a peaked structure built on the upslope side of a chimney to divert water around it. Building codes require a cricket on any chimney wider than 30 inches; without it, water and debris pile up behind the chimney and force their way under shingles. If your chimney is wider than 30 inches and has no cricket, budget $500–$900 to add one during the next re-roofing.

Should I replace the flashing when I replace the roof?

Yes—removing and reusing old step flashing often bends or cracks it, and reusing old counter flashing means missing the chance to repoint crumbling mortar joints. A good roofer will include new flashing in the estimate; if yours doesn't, ask why. Expect to pay $400–$700 extra for a full chimney reflash during a roof replacement.

How do I tell if a ceiling stain near the chimney is from flashing or the chimney crown?

Flashing leaks usually appear within 2–3 feet of the chimney base and worsen during wind-driven rain. Crown leaks (cracks in the concrete cap at the top of the chimney) show up farther from the base, often near the center of the chase, and may drip even in light rain with no wind. Check both—they can leak simultaneously. Compare notes with your ceiling water stain diagnosis checklist to rule out plumbing and HVAC sources.

This is educational information, not construction or engineering advice. Consult a licensed roofer if you find structural damage, and talk to your insurer before making claims about roof leaks to understand coverage and deductible implications.