Chimney Flashing Repair: What You Need to Know

Updated January 2025 • 5 min read

If your roof leaks near the chimney, there's about an 80% chance the flashing is the problem. It's one of the most common – and most commonly botched – roof repairs.

What Is Chimney Flashing?

Flashing is the weatherproofing system where your chimney meets your roof. It's made up of several pieces of metal that work together to direct water away from this vulnerable intersection.

A proper chimney flashing system includes:

• Step flashing: L-shaped pieces woven into the shingles along the sides
• Counter flashing: Metal embedded in the chimney mortar that overlaps the step flashing
• Base flashing: At the bottom where the chimney meets the roof
• Saddle/cricket: A ridge behind the chimney that diverts water around it

Why It Fails

Age and Weather

Metal expands and contracts with temperature changes. Sealants dry out. After 15-20 years, even good flashing starts to deteriorate.

Poor Initial Installation

A lot of flashing problems trace back to bad installation. Shortcuts like using only caulk instead of proper counter flashing, or not installing a cricket behind large chimneys.

Chimney Movement

Chimneys can shift slightly over time, separate from the house structure, or develop cracks. This movement breaks seals and creates gaps.

Roof Replacement Without Reflashing

When roofs get replaced, sometimes contractors reuse old flashing to save money. Old flashing on a new roof is a leak waiting to happen.

Signs Your Flashing Is Failing

• Water stains on ceiling near chimney
• Visible rust on flashing
• Cracked or missing caulk/sealant
• Flashing pulling away from chimney
• Gaps where flashing meets masonry
• Missing pieces (they can blow off)
• Moss or debris collecting at base of chimney

Repair vs Replace

Minor repairs – resealing, patching small gaps – might cost $150-400 and buy you a few more years.

Full flashing replacement typically runs $500-1500 for a standard chimney, depending on size and complexity.

If your flashing is original to a roof that's 15+ years old, replacement usually makes more sense than repeated repairs. You're just delaying the inevitable.

The Cricket Question

Chimneys wider than 30 inches should have a cricket – a small peaked structure behind the chimney that diverts water. Many older homes don't have them.

Without a cricket, water and debris pile up behind the chimney. This accelerates deterioration and makes leaks more likely.

If you're having flashing work done on a wide chimney that lacks a cricket, it's worth adding one. Costs $300-600 extra but prevents a lot of future problems.

Why Caulk Alone Doesn't Work

Here's something to watch for: some contractors will just smear caulk all over your flashing and call it fixed. This is a band-aid at best.

Caulk breaks down with UV exposure. It cracks with temperature changes. In Knoxville's climate, a caulk-only fix might last 2-5 years. Maybe less.

Proper flashing repair involves:

• Removing old sealants completely
• Replacing any damaged flashing pieces
• Ensuring proper overlap between components
• Setting counter flashing properly in mortar joints
• Using appropriate sealants in addition to (not instead of) mechanical protection

Who Should Do the Work?

Flashing repair is one of those gray areas. Some people say call a roofer. Some say call a mason. Here's how to think about it:

Call a roofer if:

• The flashing itself is the problem
• You need a cricket installed
• It's part of a roof replacement

Call a mason if:

• The chimney masonry is cracked or damaged
• The mortar joints where counter flashing sits are failing
• The chimney needs tuckpointing or repair

Often the answer is both. A mason fixes the chimney, then a roofer installs proper flashing. Coordinate this or find a company that does both.

Prevention

• Inspect annually – look for obvious gaps, rust, separated pieces
• Clear debris from behind the chimney regularly
• Address chimney masonry issues promptly
• When replacing your roof, insist on new flashing (don't let them reuse old)