How to Fix a Leaking Chimney: 7 Common Causes and Their Solutions

If you rely on your fireplace for warmth and efficiency in the winter, the last thing you want is a leak making it potentially unusable. As soon as you notice water coming from in or around your chimney, it's time to take action. This guide walks you through the potential causes of your leak, how and where to identify the problem, and the steps to take to solve and prevent chimney leaks.

1. Missing Chimney Cap

A chimney without a cap is essentially an open hole in your roof. As water enters your chimney flue, it will erode mortar joints and eventually cause leaks and stains around your chimney.

Solution: If you don't have a chimney cap, measure the flue tile at the top of the chimney so you can purchase the proper size. The ideal cap is stainless steel and includes a bonnet or roof twice as large as the flue opening. Follow the manufacturer's instructions to properly fasten the new cap to your flue opening.

2. Faulty Chimney Chase Cover

Beneath the chimney cap may be a chase cover with screens on each side to prevent sparks from escaping. The cover may be sagging enough that water pools on top, or water may enter through openings created by fasteners.

Solution: Chase cover replacement is a simple DIY job. Simply remove the chimney cap and fasteners affixing the current cover and swap out your existing cover for a stainless steel replacement of the same size. Follow the manufacturer's instructions to affix the new cover.

3. Cracked Chimney Crown

The layer of mortar on top of the chimney is called a chimney crown. The crown prevents moisture from entering gaps in the lining and masonry. When the crown is cracked, moisture can get through and work its way down through your chimney.

Solution: Proper crown repair involves removing the entire crown and rebuilding it using cement forms and rebar. This job is best handled by a pro due to the risk of damage to the rest of the masonry.

However, you may be able to patch small cracks using mortar and then apply a crown coat brushable sealant overtop. Monitor the crown each year to ensure that new cracks don’t form, and contact a chimney pro if they do.

4. Deteriorated Brickwork

Mortar and sometimes bricks themselves can crack and erode due to wind, water, and temperature changes. Water can then penetrate these cracks. Deteriorating brickwork may be more of an issue in areas with extreme weather and frequent freeze/thaw cycles. 

Solution: You can use mortar caulk to temporarily repair cracks you notice in your chimney's bricks and mortar. A long-term fix requires masonry skills since you'll need to remove soft mortar joints and damaged bricks before tuckpointing or installing new bricks.

5. Damaged Flashing

Chimney flashing creates a waterproof seal between the roof and the chimney. It typically lines the base of a chimney to cover gaps where it meets the roof. Damaged or improperly installed flashing won't function properly. Flashing can fail due to rust, damage, or old sealant that's lost its flexibility. 

Solution: Replace any failing sealant with a store-bought flashing repair kit, which includes reinforcement fabric and flashing sealant. Carefully scrape away defective sealant and replace it with the materials from your kit.

Otherwise, full replacement is needed. This involves removing the existing flashing, shingles, and tar paper and affixing new materials in their place. Only a trained roofer should handle this work since mistakes can lead to serious structural damage beyond the existing leak.

6. Roof Lacks a Chimney Cricket

A chimney cricket is a wedge-shaped structure on a roof that spans the width of an eave-side chimney to divert water around its sides. Without a chimney cricket, water tends to pool behind the chimney as it rolls down the roof. This can cause leaks even with adequate flashing in place.

Solution: If your chimney sits by the eaves of your home and lacks a cricket, building one may solve your leak. However, this is a challenging job that involves adding to the existing structure of your roof, so you'll want to hire a contractor for construction. The job involves measuring the chimney width and pitch, cutting away shingles, tucking flashing underneath, and sealing the roof.

7. Attic Condensation

This issue is common in gas fireplaces since they emit exhaust that can gradually form condensation inside a chimney. Without a proper liner, moisture buildup in the chimney can seep out into walls and attics.

Solution: A simple solution to condensation from gas fireplace exhaust is to install a chimney liner as a barrier between the moisture and the surrounding brick. Measure your chimney height and purchase a liner kit. Installation will vary by manufacturer but typically involves lowering the liner slowly through the chimney and attaching it to both your fireplace exhaust and the flue opening.

How Much Does It Cost to Fix a Leaking Chimney?  

Chimney repair costs $160 to $750 on average, but the cost to fix a leaking chimney will vary depending on the cause and the required repairs. For example, the cost to replace chimney flashing is $400 to $1,600 on average. Meanwhile, the average cost to replace a chimney crown is $400 to $2,200. For accurate prices in your area, contact a few local chimney services for quotes.

DIY vs. Hiring a Pro 

Chimney leak repair can be dangerous. It involves working on your roof and working on areas of your home where mistakes can lead to costly damage. Be sure you have safe access to your roof and proper protective gear if you attempt a DIY repair.

Because any improper repairs to your roof, masonry, or structural elements of your home can end up costing you much more in the long run, you’re best off contacting a professional chimney repair service near you to ensure a safe and lasting repair job backed by a warranty.

How to Prevent a Leaking Chimney

The best way to prevent chimney leaks is to practice proper chimney maintenance. Schedule professional maintenance at least once per year. A local chimney sweep will remove dangerous creosote buildup and inspect your chimney for damage. They can advise you when they notice problem areas that may turn into leaks without repair.

Proactive repairs can prevent the costly water damage that often results from leaks. Never use your chimney without ensuring it’s safe to do so.