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


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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?

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.

Chimney with no footing (C) Daniel FriedmanEven 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. Readers diagnosing chimney movement and foundation problems should also see CHIMNEY LEANING, SEPARATION, MOVEMENT: OUTDOORS, and  CHIMNEY LEANING, SEPARATION, MOVEMENT Chimney Crack & Collapse Risks. Repairs for moving chimneys are discussed at CHIMNEY LEANING, REPAIR OPTIONS.

A Catalog of the Causes of Chimney Movement

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

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).

Cracks in a concrete block chimney (C) Daniel FriedmanCracked 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:
  • Damaged, unsafe chimney liner
  • Damaged, unsafe fireplaces where the chimney has pulled the firebox away from the building or created dangerous openings around the fireplace into the building structure, risking both sparks (and fire) or air leaks (and inability to control the draft).
  • Leaks into the building walls
  • Unsafe fireplaces in the building: hearth cracks, fireplace side cracks, chimney damage all present risks of sparks or smoke entering the building cavities, a fire and flue gas risk. Check for evidence of movement at the fireplace.

Also see CHIMNEY CRACK DETECTION & DIAGNOSIS

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.

More Reading

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Frequently Asked Questions (FAQs) about Chimney Movement Causes, Diagnosis, & Evaluation

Question: chimney damage or movement caused by chimney sweep work?

I had a chimney sweep on my roof last week He cut the top off one of the clay liners to accommodate a chimney cap. After his departure I noticed the top of the chimney was moved away from the house about 1 inch. Could the chimney sweep leaning on the chimney produce enough force to move the chimney? I am absolutely sure the chimney was not away from the house prior to his work. Thanks for any help you may provide. - M.H., Woburn MA

Reply: check the chimney flue for safety ASAP

A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem such as the chimney movement you describe. And while I express opinions and give advice below, we're talking email here - not a substitute for an onsite expert. An unsafe chimney (yours, if it moved, may be unsafe) is a fire and carbon monoxide hazard risking fire or even a fatality. Sorry to sound so "scary" but when we're talking about chimneys by email I feel obligated to worry about safety first.

That said, here are some things to consider:

Watch out: your first priority is safety: Assuming that your chimney is in use, perhaps by your heating system or a fireplace, the first priority is to make sure that the chimney is safe to use. Do not delay in resolving that question. I offer "how to" advice in these notes.

  • If the chimney has moved or is damaged in any way, part of the "repair" (if it can be repaired) would normally require an understanding of the cause of the damage - otherwise a repair may be ineffective. For example, installing a poured masonry liner in an unsafe masonry chimney might not be not an effective repair if the chimney lacks a sound footing.
  • *Normally* working on a masonry chimney (as I infer from your description) should not cause it to move away from the building, but if the chimney were improperly supported or constructed that's certainly possible. I once nearly fell off of a roof when I leaned for a moment against a tall brick chimney that was not attached to the building.
  • And if the "cutting" of the top clay liner involved banging about with a hammer and masonry chisel
  • That might have disturbed the chimney. I accept that you are confident that the chimney had not moved prior to the work recently performed, though in all such cases I caution that there is a phenomenon I've seen many times over a long career, as perhaps have you: at times there was and remains is a pre-existing condition at a building that no one ever noticed until something else caused them to direct their attention in that direction. Then it appears that the condition is "new" - it may not be. And an expert can usually find compelling evidence to support the "new" vs "older" condition of a defect. I could suggest some methods if needed.

Any chimney of any type that has moved raises very important safety questions.

  • You should check the flue interior for damage and debris - start at the chimney base or cleanout door and look for freshly-broken scraps of chimney liner tile and also consider that if a chimney is or has been moving around it may be unsafe - having opened cracks into the building that could lead to a fire or flue gases entering the structure.
  • A professional chimney sweep, perhaps one certified by the National Chimney Sweeps Guild, can inspect the flue for safety - I'd make this a priority, and I'd be reluctant to rely on the fellow who installed the cap as he may not be a neutral professional. You can also call your local fire department for advice.
  • Meanwhile what you can do immediately is make sure you have working CO detectors and smoke detectors properly installed in your home

I would like to see sharp photos of the chimney cap installation, the chimney from roof and from ground, of any scraps you find, any cracks you observe, and I can offer further comment - but an onsite inspection by an expert is most important rather than my email views.

Finally, your chimney inspector might want to be familiar with NFPA 921 - if s/he is someone who is a professional and who works with fire and explosion investigations they probably know this "Guide for Fire and Explosion INvestigations". The current edition of NFPA 921 can be purchased online at NFPA 921: Guide for Fire and Explosion Investigations (Amazon) or directly from the NFPA at nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=921&cookie_test=1 - listed at our references as well: [8]

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