How to Seal Chimney Flashing and Prevent a Leaky Chimney

Sealing this small part of your roof makes a big difference in keeping you dry

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SKILL LEVEL
Simple
COMPLETION TIME
1 hour
COST
$25–$50
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What you'll need:
TOOLS
  • Ladder
  • Putty knife or scraper
  • Stiff-bristle brush
  • Caulk gun
SUPPLIES
  • Weather-resistant silicone caulk

Your home's exterior is a network of materials that keep you dry and safe from water damage. Flashing refers to metal sheets installed over gaps and transitions in a roof, especially around chimney brickwork. While damaged flashing warrants full replacement, smaller issues can still lead to moisture problems. Learn how to seal chimney flashing to close gaps in your defenses.

Buying Caulk to Seal Chimney Flashing

Many types of caulk degrade quickly when exposed to heat and weather, and you can’t use just any product to seal your chimney flashing. The best caulk for chimney flashing is a high-quality, weather-resistant silicone caulk designed specifically for roofing applications. Expect to spend an average of $25 per tube, though some products cost more.

How to Seal Chimney Flashing

man putting lead flashing around chimney
Photo: P A Thompson/ Getty Images

If you inspect your chimney and discover that the caulk around your flashing is wearing away, you need to reseal it. To seal the chimney flashing, remove the old caulk and clean the surface of the flashing. Then, carefully apply new weather-resistant silicone caulk along flashing edges and in mortar joints.

  1. Inspect the Chimney Flashing

    Start with a close inspection of the caulk on your chimney flashing. Telltale signs that it needs to be sealed include dry or flaking areas, visible gaps between the caulk and the brickwork, or sections where the caulk is missing completely.

    If your flashing is seriously damaged, or if you discover spongy areas underneath, then simply sealing it won't suffice. Instead, you'll need to replace the chimney flashing, which is a much more complex and risky project to DIY.

  2. Remove Old Sealant Material

    Use a putty knife or scraper to remove old, dried-out caulk material. Be careful not to damage the surrounding brickwork or the flashing itself in the process, and avoid pulling the flashing away from the chimney.

  3. Clean Off Debris

    Use a stiff brush to scrub the area around the flashing to remove moss, grime, dust, and other debris. Leaving debris on any surface will prevent your caulk from holding properly.

  4. Apply New Silicone Caulk

    Use your caulk gun to carefully apply caulk to the following areas:

    • Along the top edges where the flashing meets the chimney

    • In mortar joints where flashing is inserted

    • Over nail heads

    Use your putty knife or scraper to smooth the caulk into an even layer. Avoid air gaps to ensure an effective seal. Allow the caulk to dry per the manufacturer's instructions, then inspect your work and repeat as needed to correct any gaps or flaws in the seal.

DIY vs. Hiring a Pro 

Sealing chimney flashing as a DIY project is inexpensive and takes very little time. The cost to seal a chimney can be much higher if you hire a pro, since labor alone will cost $130 or more.

However, any project that involves working on a roof is inherently risky for homeowners. You should always have a spotter when working on a ladder or roof. Additionally, removing material from a chimney poses a risk to the masonry, which can be costly to repair.

To avoid the risk of personal injury or damage to your roof or chimney, consider hiring a local roof repair company to handle sealing your chimney flashing.

Frequently Asked Questions

Schedule professional fireplace service in late summer before the busy fall season begins. Test your damper and inspect the chimney cap in October to ensure summer storms caused no damage. Throughout the OH winter, monitor your system for unusual odors or smoke backdrafts. Once spring arrives in Columbus, inspect the exterior masonry for freeze-thaw damage and schedule any necessary concrete repairs immediately.

Helpful?

When hiring a professional for fireplace service, watch out for quotes that skip a video chimney inspection. Older Columbus homes contain aging clay liners that demand thorough assessment. Reject contractors who promise fast timelines without an initial inspection or ignore local permit requirements. Always demand references from past OH projects to ensure the contractor understands local structural and soil conditions.

Helpful?

The best materials for fireplace service must withstand severe freeze-thaw cycles. Install stainless steel flexible liners and concrete crowns to resist winter damage. Use high-temperature refractory mortar to handle structural settling caused by heavy Columbus clay soils. A top-mounted damper is essential to block cold OH drafts and prevent wildlife from entering. Always require proper firebrick for any internal firebox repairs.

Helpful?

Completing fireplace service directly boosts your home's resale appeal in Columbus. Buyers in historic neighborhoods place a high premium on functional, well-maintained hearths. State disclosure laws require sellers to report known chimney defects, so a documented, functional system gives you a distinct advantage during appraisals. A working fireplace makes your property stand out to buyers, especially during cold OH winters.

Helpful?

Proper fireplace service provides crucial supplemental heat and eliminates cold drafts during freezing Columbus winters. Repairing dampers and sealing flues directly stops freezing air from entering your living space. A well-maintained chimney also vents dangerous combustion gases safely outside, protecting your indoor air quality. Servicing your system prevents moisture intrusion and stops local OH wildlife from nesting inside your chimney.

Helpful?
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