Photograph of a brick chimney cracked exterior, possibly due to heat. Masonry Chimney Crack Inspection & Diagnosis

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Diagnose cracks in chimneys:

This article catalogs the types of chimney cracks and movement that may be found in brick, stone, or concrete block chimneys; we describe the inspection and and diagnosis of the cause of each type of chimney cracking and we suggest the probable severity, safety concerns, and chimney repairs that may be necessary.

We include links to additional detailed articles about each type of chimney cracking or movement.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Cracked Brick Masonry Chimney Sides

Photograph of a brick chimney cracked exterior, possibly due to heat.This article series on chimneys, chimney construction, 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.

Guide to Diagnosing & Evaluating Cracks in Brick Chimneys

Our brick chimney photographs just above illustrate a common (and dangerous) crack pattern found in corbeled (stair-stepped) chimneys where a brick chimney passes through an attic floor and is angled over to exit at the chimney ridge.

At the chimney in our photo at above left, look very closely at the masonry joint where the chimney begins its transition from vertical to angled.

To prevent cracks in a leaned-brick chimney such as this one, the chimney depends on absolutely stable support by the roof framing structure where it passes through the roof to outside.

Unless the brick chimney was adequately supported and constructed it may lean, causing the crack pattern we show below.

Watch out: often the crack in a leaning brick chimney occurs at the attic floor where the chimney begins its transition from vertical to angled - a spot where the crack may be hard to spot.

Photograph of a brick chimney cracked exterior, possibly due to heat.

See CHIMNEY INSPECTION INDOORS for a discussion of chimney movement that opens a hard-to-find crack where a corbeled brick chimney passes through an attic floor.

List of Typical Causes of Cracks in Brick Masonry Chimneys & Flues

Photograph of a damaged masonry chimney.Cracks in a brick masonry chimney such as shown in these photographs may be caused by improper original chimney construction. This damage also appears on concrete block constructed chimneys.

The second cracked chimney at above right is a bit more suspect because we see what might be traces of soot or creosote having washed out through the cracks to the chimney exterior. If this proves to be the case this flue is certainly seriously damaged.

Frost Cracking in Brick Chimneys & Flues - outdoor & indoor evidence of brick chimney damage

Frost cracked brick chimney viewed in attic (C) DanieL Friedman

At left we show a very common crack pattern found in brick masonry chimneys & flues - water and frost cracking at the chimney top.

Considering that there is a nice thick concrete chimney cap. why do we have this brick movement and mortar-joint cracking?

Perhaps the chimney cap is cracked, flat, not draining, or it was not sealed around the flue, or a rain cap was missing.

See CHIMNEY CAP & CROWN DEFINITIONS for detailed examples of defects at the chimney top that lead to this type of chimney damage.


At below left we show a very common crack pattern found in brick masonry chimneys & flues - a collection of vertical, diagonal, and even some horizontal chimney cracks that are probably due to a combination of water intrusion and (in freezing climates) frost cracking.

Frost cracked brick chimney viewed in attic (C) DanieL Friedman

Even if you do not immediately notice the chimney cracks themselves you are likely to spot this chimney damage by the creosote stains carried to the chimney surface by water entry into the chimney flue.

Of course had these cracks and stains been present on a hidden side of the chimney, say between the chimney and a close-by gable-end wall, you'd not see these clues from within the attic.

But inspecting this chimney outside, if it has had no proper rain cap and chimney cap you should be extra alert for water and frost damage to the chimney and its flue.

A second set of clues - water leak stains, may be visible in a fireplace or at a chimney cleanout lower in the building.

Thermal Cracking in Brick Chimneys & Flues May Produce Thin Vertical Openings

Photograph of a brick chimney cracked exterior, possibly due to heat.

At left we show a very common crack pattern found in brick masonry chimneys & flues - a vertical crack that begins in a mortar joint and extends through individual bricks themselves.

Cracked chimney masonry such as shown in the photo of cracks in a brick chimney exterior (at left), may a safety concern if the flue liner or chimney are not intact and fire/gas safe.

The brick chimney crack type shown here is more often caused by thermal expansion (and improper chimney construction) than by frost - frost cracking is often more visually obvious and is often accompanied by brick spalling.




Severe Chimney Cracking - Deteriorated, Collapsing Brick or Masonry Block Chimneys

Split brick chimney in a basement (C) Daniel FriedmanSevere chimney cracks that risk imminent chimney collapse, flue gas leaks, and fire hazards, are discussed and illustrated in detail


There we also describe a case of an imminent catastrophic chimney collapse

Also see our discussion


Watch out: Cracks in a chimney can be very significant and dangerous, risking fire or chimney collapse.

Be sure to review the dangerous chimney collapse warnings at


Cracks in Masonry Block or Concrete Block Chimneys

Cracks in a concrete block chimney (C) Daniel Friedman

Cracks in a masonry chimney, particularly concrete block chimneys are often caused by

See CRACKED CHIMNEYS, MASONRY BLOCK for details and additional photographs of concrete block chimney cracking.

Chimney Cracks due to Chimney Movement, Tipping, Leaning

Chimney separation at house (C) D Friedman A Puentes

Chimneys that lean, curve, bulge, tip, or otherwise move due to footing settlement and tipping or due to failure to secure a tall chimney to the building also may produce both visible cracks on the chimney exterior and hidden cracks and damage to the chimney flue.

The risk of an unsafe chimney flue lies behind our advice that a thorough inspection of the entire chimney flue is necessary when there is any evidence of chimney movement.

See CHIMNEY LEANING, SEPARATION, MOVEMENT: OUTDOORS for details of the detection, analysis, and repair of leaning and tipping chimneys and chimneys that have separated from their building.

Curved Brick Masonry Chimneys

Photograph of a damaged unsafe brick chimney viewed from outside.

Especially on older buildings using brick chimneys, and more so where the chimney flue is not lined with a modern clay liner, brick chimneys may be seen to curve in one direction.

Often all of the similar chimneys in a neighborhood curve in the same direction. It's not a coincidence. A brick chimney will often curve away from its most weather-exposed side due to sulphation - expanding brick mortar joints caused by the combination of water and sulphur or other minerals.

See CURVED BRICK CHIMNEYS, SULPHATION for further explanation of the cause, significance, and cure of curved brick chimneys.


Continue reading at CRACKED CHIMNEYS, MASONRY BLOCK or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see CHIMNEY CRACK DETECTION & DIAGNOSIS FAQs - questions & answers posted originally on this page.

Or see these

Chimney Collapse / Crack Articles

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CHIMNEY CRACK DETECTION & DIAGNOSIS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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