Water leaking into a chimney base (C) Daniel FriedmanWater Leaks & Frost Damage to Chimneys & Flues
Where do chimney leaks occur, how are they fixed?

  • CHIMNEY DAMAGE by LEAKS & FROST - CONTENTS: How water and moisture leak into and damage chimneys and heating appliances. Chimney inspection, diagnosis, and repair for water or frost damaged chimneys and flues.
  • POST a QUESTION or READ FAQs about how to spot water or frost damage to chimneys & how that chimney damage may be repaired

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Water damage to chimneys & flues:

This article describes water leaks and moisture that damage masonry and metal chimneys and the heating appliances that are connected to them. We list the common sources of water and leaks and we include warnings for inspectors who need to examine equipment as well as the chimney itself when water or moisture leaks are detected.

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Moisture Problems that Damage Chimneys

Water leaking into a chimney base (C) Daniel Friedman

Our photo (page top) shows water pouring into a basement, coming out of the chimney cleanout during a heavy rainstorm. Readers of this article should also see CHIMNEY COLLAPSE RISKS, REPAIRS.

These articles on chimneys and chimney safety provide detailed suggestions describing how to perform a thorough visual inspection of chimneys for safety and other defects. Chimney inspection methods and chimney repair methods are also discussed.

Our photograph at left shows a stunning waterfall flowing out of a "sealed" chimney cleanout in a basement. Lots of roof spillage or surface runoff was entering the base of this chimney.

[Click to enlarge any image]

Moisture is the major cause of chimney corrosion and disintegration in both masonry and metal chimneys. The flue gases are acidic in nature and if allowed to condense and saturate the masonry or joints in metal flues the destructive results will soon be apparent.

Mechanical problems in the construction or settlement after construction and over firing or flue fires will also contribute to the problems.

External moisture enters the chimney through cracked caps, porous masonry, poor mortar joints and improperly designed and installed roof flashings. Internal moisture (condensation) collects in cracked or separated flue tiles, blocked flues and chimney caps.

Masonry chimneys subjected to moisture damage can have efflorescent salt stains, spalled bricks, eroded mortar joints, flaked cracks in the ceramic flue liner and cracked caps.

Metal components of a vent system can have rust and white acid stains at joints, corrosion holes along the bottom of horizontal connectors and corroded chimney cleanout doors at the base of the flue.

Moisture enters a chimney structure from several locations:

Water leaks into a Chimney can Damage the Chimney and the Appliances Connected to It

The result of leaks into a chimney can be unsafe heating equipment as well as costly damage to the chimney, the appliances connected to it, and to the building itself.

Where do Most Leaks Occur at Chimneys?

Question: We can't find the leak in our chimney

Chimney cap slope (C) Carson Dunlop Associates2017/09/10 Laura said:

Our chemney leaks every time it rains heavy.

We have had a builder and roofer out over thelast two years who have made various changes (or they told us they have), however its stil dripping and letting rain water in. Any ideas?

This question and our reply were posted originally at CHIMNEY CRACK DETECTION & DIAGNOSIS

Sketch above / left showing improper slope on the masonry cap of a chimney and also the omission of a rain cap atop the chimney flue and our chimney drawing below were provided by Carson Dunlop Associates, a Toronto home inspection, report writing & education firm.

Reply: where to look for leaks on or around chimneys


It sounds as if the people working on the problem have tried solutions without finding the actual leak source.

I'd start by trying to find, more accurately, just where water is coming in to the building:

You might get a more clear understanding of the leak by asking for an inspection by a chimney sweep who's certified (National Chimney Sweeps Guild) and who can examine both the entire exterior and the entire flue interior of the chimney to see where water is originating.

I suggest preparing yourself by reading over some of the chimney leak diagnosis and repair articles I'll give below, to become familiar with the different types of leaks that occur in or on or around chimneys.

Lost rain cap (C) Carson Dunlop Associates

Note that some of these leak problems occur only on brick or other masonry chimneys while others like CHIMNEY CHASE CONSTRUCTION will discuss leak points that only occur around the top of a wood-framed and enclosed metal chimney.

CHIMNEY DAMAGE by LEAKS & FROST - How water and moisture leak into and damage chimneys and heating appliances.

CHIMNEY STAINS & LEAKS - stains can help track down where water is getting into a chimney - where I have posted your question and my reply

FLASHING, CHIMNEY MISTAKES & LEAKS - leaks where a chimney passes through a roof or eaves or soffit

CHIMNEY CRACK DETECTION & DIAGNOSIS - leaks may occur in a masonry chimney that is damaged by frost, settlement, movement - such chimneys are probably unsafe

CHIMNEY SHOULDER LEAKS - if it's a brick chimney there may be leaks along the point where the chimney widens out as it nears its base

CHIMNEY CHASE CONSTRUCTION if it's a wood-framed chimney chase and metal flue

CHIMNEY REPAIRS, TOP & CLAY FLUE TILE for leaks at the top seal or top of the chimney


Continue reading at CHIMNEY INSPECTION at ROOFTOP or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see CHIMNEY CAP & CROWN DEFINITIONS the difference between a chimney rain cap and a chimney top seal - two different possible leak problems.

Or see CHIMNEY WET TIME & CORROSION - effects of moisture on metal chimneys & flues


Suggested citation for this web page

CHIMNEY DAMAGE by LEAKS & FROST at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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