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Fix a chimney that leaks

We'll confirm where the chimney leaks—flashing, crown, mortar, or cap—then repair the seal or tell you when to call a roofer or mason.

Troubleshooting · Home maintenance
1–3 hours
What you'll need
  • Roofing cement or flashing sealant
  • Chimney crown repair sealant (if crown is cracked)
  • Ladder (sturdy, with spotter)
  • Putty knife or trowel
  • Wire brush (for cleaning)
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Steps

Goal: Confirm the leak source, then isolate and repair flashing, crown, mortar, or cap.

  • Check where water appears—attic near the chimney, ceiling below, or inside the fireplace. Water during or right after rain points to the chimney or roof.
  • Good: Water or stains correlate with rain. Proceed to Check flashing.
  • Bad: Water appears without rain—may be condensation or a different source. See When to get help.

Check flashing

Goal: Inspect and repair the roof-chimney seal—the most common leak source.

  • From the roof (use a sturdy ladder and have a spotter), inspect the flashing where the chimney meets the roof. Look for gaps, rust, loose metal, or missing step flashing.
  • If you see small gaps or loose edges, clean the area and apply roofing cement or flashing sealant to seal the joint. Tuck the base flashing under the shingles if it has pulled away.
  • Good: Flashing is sealed. Test with rain or hose.
  • Bad: Flashing is severely rusted, bent, or missing sections—call a roofer.

Crown and mortar path

Goal: Inspect and repair the chimney crown and mortar joints.

  • Inspect the chimney crown—the concrete slab on top of the chimney. Look for cracks, chips, or missing overhang. For small cracks, clean and apply chimney crown repair sealant per the product label.
  • Inspect the mortar between bricks. Cracked or missing mortar lets water in. If joints are hairline or minor crumbling and bricks are stable, repoint—see fix-mortar-is-cracked.
  • Good: Crown is sealed and mortar is intact or repointed.
  • Bad: Crown is crumbling, mortar is stair-step or horizontal, or bricks are loose—call a mason.

Check chimney cap

Goal: Confirm the chimney cap is present and intact.

  • Confirm the chimney cap is present and covers the flue opening. A missing or damaged cap lets rain, snow, and debris into the flue.
  • If the cap is missing, install one that fits your flue size. If it is rusted or bent, replace it.
  • Good: Cap is in place and intact.
  • Bad: Cap is missing or damaged—install or replace.

When to get help

Call a roofer if:

  • The flashing is severely damaged, rusted through, or needs replacement.
  • You are not comfortable working on the roof.

Call a mason if:

  • The chimney crown is crumbling or has large gaps.
  • Mortar damage is widespread, stair-step, or bricks are loose.

Verification

  • No new water entry in the attic, ceiling, or fireplace during or after rain.
  • Flashing is sealed with no visible gaps at the roof-chimney joint.
  • Chimney crown has no open cracks; mortar joints are intact or repointed.
  • Chimney cap is present and covers the flue opening.

Escalation ladder

Work from the device outward. Stop when the problem is fixed.

  1. Confirm leak source Verify water enters during rain; note where it appears (attic, ceiling, fireplace).
  2. Check flashing Inspect the roof-chimney joint for gaps, rust, or loose metal.
  3. Check crown and mortar Inspect the crown for cracks; inspect mortar joints for damage.
  4. Check chimney cap Confirm the cap is present and intact.
  5. Call a pro Severely damaged flashing, crumbling crown, or unsafe to work on roof—call a roofer or mason.

What to capture if you need help

Before calling support or posting for help, have these ready. It speeds everything up.

  • Where water appears (attic, ceiling, fireplace)
  • Flashing condition (gaps, rust, loose)
  • Crown condition (cracks, chips)
  • Mortar joint condition
  • Chimney cap present and intact
  • Steps already tried

Does water enter during or after rain?

Check the attic near the chimney, ceiling below, or inside the fireplace. Water that appears with rain points to the chimney or roof.

Confirm where water appears. Good: water or stains correlate with rain—chimney or roof leak. Bad: water appears without rain—may be condensation or a different source (plumbing, HVAC).

Yes No

You can change your answer later.

Water may not be from chimney

If water does not appear during or after rain, the source may be elsewhere—check plumbing, HVAC, or condensation. This guide is for chimney leaks. See how-to-find-water-leak for general leak tracing.

Done

Is the flashing damaged or has gaps?

The flashing seals the roof-chimney joint. Gaps, rust, or loose metal let water in.

Inspect the flashing from the roof. Look for gaps, rust, loose metal, or missing step flashing. Gaps or minor rust: reseal with roofing cement or flashing sealant. Severely rusted or missing: call a roofer.

Yes No

You can change your answer later.

Reseal flashing and test

Clean the area and apply roofing cement or flashing sealant to close gaps. Tuck base flashing under shingles if it pulled away. Test with rain or hose. If water still enters, check crown and mortar.

Done

Is the chimney crown cracked or damaged?

The crown is the concrete slab on top of the chimney. Cracks let water in.

Inspect the chimney crown. Small cracks: seal with chimney crown repair sealant. Crumbling or large gaps: call a mason.

Yes No

You can change your answer later.

Seal crown and test

Clean the crown and apply chimney crown repair sealant per the product label. The crown should slope away from the flue. Test with rain or hose. If water still enters, check mortar and cap.

Done

Are mortar joints cracked or missing?

Cracked or missing mortar between bricks lets water into the chimney.

Inspect the mortar joints. Hairline or minor crumbling, bricks stable: repoint—see fix-mortar-is-cracked. Stair-step, horizontal, or loose bricks: call a mason.

Yes No

You can change your answer later.

Repoint mortar and test

Rake out old mortar, clean, dampen, and repoint with type N or S mortar. See fix-mortar-is-cracked for full steps. Test with rain or hose.

Done

Is the chimney cap missing or damaged?

A missing or damaged cap lets rain and debris into the flue.

Check the chimney cap. Missing or damaged: install or replace a cap that fits your flue size. Intact: if all checks pass and water still enters, call a roofer or mason.

Yes No

You can change your answer later.

Install or replace chimney cap

Install a chimney cap that fits your flue size. Metal or mesh caps are available at hardware stores. Test with rain or hose. If water still enters, call a roofer or mason.

Done

Call a roofer or mason

Call a roofer if the flashing is severely damaged or needs replacement. Call a mason if the crown is crumbling, mortar damage is widespread, or bricks are loose. Call a pro if you are not comfortable working on the roof.

Done

Reviewed by Blackbox Atlas

Frequently asked questions

Why does a chimney leak?
Common causes: damaged or poorly installed flashing (roof-chimney seal), cracked chimney crown, cracked or missing mortar joints, or a missing or damaged chimney cap. Water follows the path of least resistance—often the flashing first.
Can I fix a chimney leak myself?
Yes, for minor issues: resealing flashing with roofing cement, patching small crown cracks, or repointing mortar joints. If the flashing is severely rusted or damaged, the crown is crumbling, or you are not comfortable on the roof, call a roofer or mason.
When should I call a pro for a chimney leak?
Call a roofer if the flashing is severely damaged or you need to replace it. Call a mason if the chimney crown is crumbling, mortar joints are widespread, or bricks are loose. Call a pro if you are not comfortable working on the roof.

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