Roof flashing repair: how to stop leaks around chimneys and vents

By Daniel Brooks, Home maintenance writer and appliance troubleshooting specialist based in Charlotte, NC. Reviewed [date — human adds].

Quick answer

Roof flashing repair means resealing or replacing the metal strips that seal joints around chimneys, vents, and skylights. It's one of the most common causes of a roof leak, and also one of the more DIY-accessible ones, as long as the roof pitch and weather cooperate. If you haven't yet confirmed flashing is the actual source of your leak, the full roof leak diagnostic walks through the broader triage first.

Safety first

Don't climb onto the roof in wet, icy, or high-wind conditions. Use a ladder that's stable and secured at the top and bottom, wear shoes with rubber soles for grip, and have a second person around while you're up there. Chimney flashing sits in a higher-traffic area of the roof than most repairs, so take your time getting positioned before you start working.

Confirm it's actually the flashing

Before buying materials, make sure flashing is really the source. Most chimneys use two flashing pieces working together: step flashing, individual L-shaped pieces woven between each shingle course up the side of the chimney, and counter-flashing, a strip embedded into the mortar joints above it that overlaps the step flashing and sheds water over it. A gap opening up between the two is one of the most common places a leak starts.

Look for:

A visible gap between the metal flashing and the surrounding shingles or roofing material
Rust spots or actual holes forming in the metal itself
Sealant along the flashing edges that's dried out, cracked, or pulled away
A section of flashing that's visibly lifted, bent, or no longer sitting flush against the roof

A leak that shows up specifically near a chimney, a plumbing vent, or a skylight points strongly toward flashing rather than shingle damage somewhere else on the slope.

Fixing it, from simplest to most involved

Work through these in order. Most flashing problems stop at step 1 or 2.

Reseal existing flashing

If the metal itself is intact but the seal along its edges has failed, clean out any old, cracked sealant with a putty knife, then apply a fresh bead of roofing cement or sealant along the joint. This is the fastest fix and handles a large share of flashing leaks on its own.

Re-secure flashing that's lifted or loose

If a section has come loose from its fasteners but isn't damaged, refasten it with roofing nails and reseal the edges. Check that the flashing sits flat against the roofing material before sealing; a piece that's still slightly lifted will leak again even with fresh sealant on top.

Replace a short section of damaged flashing

If the metal is rusted through or cracked, resealing won't hold. This means lifting the shingle course above the damaged section, removing the old flashing, and sliding in a new piece cut to match. It's more involved than the first two steps but still within reach for someone comfortable with basic roofing tools.

Full flashing replacement, beyond DIY scope

Replacing an entire chimney's flashing system, or valley flashing that runs the length of a roof seam, generally means removing more shingles and working with masonry counter-flashing. This is the point where most homeowners bring in a roofer rather than continuing solo.

Materials you'll need

Roofing cement or roofing sealant (see the distinction below)
Replacement flashing, aluminum or galvanized steel, matched to what's already on the roof
A flat pry bar for lifting shingles
Roofing nails
A caulking gun if using a cartridge-style sealant

When to call a roofer

Call a roofer if multiple flashing points are failing at the same time, which often signals broader roof age issues rather than one isolated problem. Also call one if the flashing is integrated with a chimney crown that's cracked or deteriorating, since that's a masonry repair outside the scope of roofing work. Any structural concern, like a soft or sagging deck near the flashing, is a stop-and-call situation too.

Photos for this guide

Roof flashing around a chimney with a visible gap causing a leak. — Real photo of flashing around a chimney or vent showing a visible gap or lift.

PHOTO — human adds

Real photo of applying roofing cement to a flashing seam.

FAQ

How do I know if a roof leak is caused by bad flashing?

Check for a visible gap between the metal flashing and the surrounding shingles, cracked or peeling sealant along the edges, or flashing that looks lifted or bent away from the roof surface. Leaks that appear specifically near a chimney, vent pipe, or skylight point strongly to flashing rather than shingle damage.

Can I repair roof flashing myself, or does it need a roofer?

Resealing intact flashing with roofing cement, or re-securing a section that's come loose, is a reasonable DIY task for anyone comfortable on a ladder and a low roof pitch. Replacing rusted or badly damaged flashing sections, or anything tied into chimney masonry, is more involved and often worth hiring out.

What's the difference between roofing cement and roofing sealant for flashing repair?

Roofing cement is a thick, tar-based product best for filling gaps and bonding flashing to a roofing surface. Roofing sealant, often a polyurethane or silicone caulk, works better for smaller cracks and edges where a cleaner finish matters. Both work for flashing repair, and many small jobs use both together.

How long does a roof flashing repair typically last?

A properly resealed or replaced flashing section, using material matched to your roof type, typically lasts as long as the surrounding roofing material, often 15 to 20 years. A quick sealant-only patch on badly rusted flashing is a shorter-term fix and should be checked yearly.