Photograph of a curved chimney separating from a building, viewed from outside. What Causes Leaning Moving Separating Chimneys?

  • CHIMNEY MOVEMENT CAUSES - CONTENTS: What causes chimney movement or collapse - chimney footing, support, construction, or other defects. Ground-level chimney inspections: curved, collapsing chimneys
  • POST a QUESTION or READ FAQs about the causes of chimney separation from the building, cracking, leaning, or other chimney movement problems

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Diagnose movement in chimneys:

This article describes chimney inspection procedures and critical chimney defects which can be observed from outdoors at ground level. We begin with the detection of chimney movement, its causes, its symptoms. These articles continue with other chimney defects that can be found by visual inspection from outdoors at ground level, then from an on-roof inspection, followed by indoor inspections and ending with chimney-flue interior inspections.

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What Causes Chimney Movement, Leaning, or Separation from a Building?

Chimney with no footing (C) Daniel Friedman

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.

Defective or Missing Chimney Footings Cause Cracks, Leaning, Movement, or Collapse

Masonry chimneys represent a heavy concentrated load on the soil or support structure. Therefore, proper footing support is critical and is generally separated from the building footings except possibly at the exterior wall.

It should not come as a surprise that some masonry chimneys are constructed with an inadequate footing, or no supporting footing whatsoever. Future settlement, movement, tipping, or separation of the chimney from the building is certainly likely in such installations.

Even a casual inspection from outside would raise the question about the absence of a footing for the chimney shown in our photo. You will notice the erosion of soil from below a little concrete skirt around the chimney base of this concrete block chimney.

On occasion you may find that the chimney was built on bedrock, taking advantage of a natural footing. Inspecting in a crawl space or basement where the bedrock is visible may reduce the anxiety of the inspector in such cases.

[Click to enlarge any image]

Homes built upon dry-laid stone foundations may have a chimney installed with its base sitting atop the foundation wall itself. Those chimneys might be stable, but be sure to review our warnings about dead end flues that are usually in use where such chimneys were built with no extension very far below ground level.

We provide a series of articles on diagnosing chimney cracks and movement include Chimney Movement - Causes, then CHIMNEY MOVEMENT, ONGOING vs STATIC where we describe determining whether chimney movement is ongoing.

A Catalog of the Causes of Chimney Movement

Causes of chimney movement and separation (C) Carson Dunlop Associates

Carson Dunlop Associates [at REVIEWERS] sketch shows a number of common causes of chimney movement. Understanding the cause of movement informs the choice of repair methods. Three of these have to do with the chimney footing:

  1. Bad soils supporting the chimney footing, combined with weak or eroded soils, frost heaves, or expansive clay soils under the footing; if a chimney was added after the building construction and backfill were complete there is an increased chance that the chimney footing was placed on soft backfill that later settled.
  2. Deteriorated chimney footing, perhaps from water, frost, poor quality of concrete used, loose stone construction, placement on top of an unstable stone foundation wall
  3. Undersized chimney footing, such as a footing that does not project sufficiently past the chimney base to support its weight on the soil below, or a footing that was cast too thin, resulting in breakage.
  4. Excessive chimney corbelling (stair-stepped brick work) - often found inside attics of older homes - look closely at the junction between the beginning of the corbelled chimney section and the top of the last course of vertical brick masonry for gaps. Often this detail is hard to see because it is at or inside the attic floor.
  5. Deteriorated chimney mortar leading to loose or falling chimney sections
  6. Missing or inadequate lateral support tying the chimney to the structure. Lateral support stabilizes a tall chimney, but lateral support is unlikely to handle the weight of a falling or leaning masonry chimney caused by other conditions in this list.
  7. Mechanical damage to the chimney - such as leaning a ladder against a tall flue, perhaps combined with weight of a scaffold during chimney repair or roof repair work, or by falling tree limbs.

Other chimney movement gaps include caulk or even wood or metal flashing covering the gap between the chimney and the building.

If the chimney has recently moved, say since the last "repair" you will see a new gap or you may see a line on the chimney where a sealant that used to touch the building has torn away from the building but remained attached to the chimney side.

Such chimneys are unlikely to be safe, probably need major repairs, and are likely to need to be replaced entirely.

If we see a leaning or moving chimney that already has been re-lined we speculate that it may have been inspected and repaired but we'd still want to know just what was done.

If the chimney moved further after the liner was installed, connections between vented appliances or a woodstove and the chimney flue liner could have opened and thus might be unsafe.

See CURVED BRICK CHIMNEYS, SULPHATION for a description of apparent chimney movement caused by the combination of a missing flue liner and sulphation.

Cracked Concrete Block Chimneys

Cracks in a concrete block chimney (C) Daniel Friedman

Both outdoors and indoors we may also see chimney cracks which could be due to chimney movement (introduced above) or due to compression loads or other chimney construction problems (just below).

Cracked concrete block chimneys: Our photo at left shows dangerous cracking indoors in a concrete block chimney used to vent a heating appliance. (You might also notice that the barometric damper is not level - a much simpler problem to correct.) As a chimney leans away from the house we might find several problems:


The usual repair is to remove and replace the chimney, though in some cases it may be possible to re-line a chimney and to jack an intact masonry chimney back to level and repair its connections into the building.

Goofy Moving Chimney Repairs and Attempts to Hide Chimney Movement

Photograph of a brick chimney separating from the building.

Attempts to hide chimney movement can be dangerous since if there is a safety problem the building owner or inspector may not pick up its clues.

The fresh and thick band of caulk between the chimney and the wall as shown in this photograph were traced to a chimney separation that had been "repaired" simply by more caulking at the wall.

Because caulk is flexible, if it has been recently applied caulking may hide an ongoing chimney movement problem. But even if the chimney is no longer moving (or we think it is not moving) an inspection for flue safety and fireplace safety are essential.

In the next article in this series, Ongoing Chimney Movement, we provide a detailed example of a chimney which probably moved continually over many years, and which produced a wide gap between the chimney side and the building.

at CHIMNEY MOVEMENT, ONGOING vs STATIC we continue this article with a case reporting evidence of ongoing chimney movement, repeated repairs, and the need to remove and rebuild a large masonry chimney.

Chimney Leaning, Damage, Repair Articles


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



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