Leaning or separating chimney

When it is urgent

A chimney that has moved may also have cracked flue tiles or a connection that has pulled apart inside the house, which can let smoke or carbon monoxide escape. Make sure carbon monoxide alarms are working. If one sounds, leave the house and call 911. If you think the chimney is about to fall, get people clear of it first.

Two very different problems

A leaning chimney usually falls into one of two broad categories, and telling them apart shapes everything that follows.

Movement from the base

The whole chimney is rotating or sinking because the footing below it has settled, cracked or was never adequate. The chimney may stay fairly intact as a unit while it tips away from the house. Common clues include a gap between the chimney and siding that is wider at the top than at the bottom, cracks in the foundation or footing area, and cracks in the hearth or firebox.

Upper-stack deterioration

The base is stable, but the part of the chimney above the roof has weakened. Water, freeze-thaw cycles and eroded mortar let the top section shift or bow. Clues include a lean that starts above the roofline, loose or missing brick near the top, open mortar joints and a damaged crown. The house wall and foundation may show nothing unusual.

The categories can overlap, and only an on-site evaluation can tell which is happening.

What makes chimneys move

InterNACHI, a home inspection association, lists several causes of chimney leaning and collapse:

• Footing problems. Footings that are undersized, too shallow, cracked or deteriorated by water and frost.
• Soil problems. Erosion, settlement, frost heave and expansive clay under the footing. Downspouts that dump water at the base of the chimney can make this worse.
• Mortar deterioration. Mortar that crumbles easily leaves the brick with little holding it together.
• Missing lateral support. InterNACHI notes that chimneys without steel straps or ties to the house structure are more vulnerable.
• Outside forces. Wind, falling tree limbs and storm damage.

In older New Jersey homes, years of water entry at the top combined with freeze-thaw can turn an upper stack loose even when the footing is fine. Additions and grading changes can also alter how water drains near an exterior chimney.

Signs to watch for

• A visible tilt when you sight along the chimney from the street or the side yard.
• A gap between the chimney and the siding, trim or roof that was not there before.
• Flashing that has pulled away or torn.
• Vertical cracks running through brick, not just along mortar joints.
• Cracks inside where walls or ceilings meet the chimney, or a fireplace surround separating from the wall.
• Doors or windows near the chimney that start sticking.
• Brick or mortar debris collecting on the roof or ground.

InterNACHI recommends measuring gaps and checking them over time. A simple way to do that is to mark the edges of a gap with a pencil line and the date, photograph it with a ruler for scale, and recheck after a few weeks. Growth is an important clue. Do not climb onto the roof to do this.

What an evaluation involves

The Chimney Safety Institute of America describes a Level 2 inspection as the level called for after an external event or an operating malfunction that may have affected the chimney. A thorough evaluation of a moving chimney typically covers:

• The exterior from the ground and, when safe, from the roof, including the crown, mortar and brick condition.
• The relationship between the chimney and the house: gaps, flashing, framing and any ties.
• The attic and basement sides, where the chimney passes through.
• The flue, using a camera when the flue allows, because movement often cracks or offsets flue tiles.
• The firebox and hearth.

When the evidence points to the footing or foundation, a structural engineer's evaluation is often the right next step before any repair is designed. We will tell you when that is the case.

Repair options, broadly

Patching cracks or caulking a gap does not stop a chimney from moving. Flue damage found during the evaluation may also need flue repair or a new liner. For more on how to weigh the options, see Repair or rebuild a chimney? and our chimney rebuilding page.

What we can and cannot tell you

A chimney evaluation can show whether the chimney is moving as a unit or coming apart above the roof, whether the flue has been damaged, and what masonry work would make the upper structure sound. Diagnosing foundation or soil movement is structural engineering. When footing or soil movement looks likely, we say so in our findings and recommend that you have it assessed by an engineer before major work is planned.

If the chimney is unused, removing it may be an option worth considering. See Should you remove an unused chimney?

Factory-built chimneys and chases

Not every chimney that looks like brick is masonry. Many homes have a factory-built fireplace with a metal chimney pipe inside a framed chase, covered with siding, stucco or a thin brick veneer. These chases can also move, though the causes are different.

A framed chase can sag or pull away when its framing rots from a leaking chase cover, when it was not tied properly to the house, or when its support below has settled. Because the metal chimney pipe inside depends on correct sections, joints and clearances, movement of the chase can disturb the pipe too.

The warning signs are similar: a gap at the house, a tilt, cracking stucco or siding, and water stains inside. The evaluation also covers the chase framing and the metal chimney system, and the manufacturer's installation instructions guide what can be repaired. See Masonry vs. factory-built chimneys.

Why water at the top matters for structure

It is easy to think of water problems and structural problems as separate. On chimneys they are often the same problem at different stages. A cracked crown or missing cap lets water into the top courses. Each winter, freezing water loosens mortar and brick. Over years, the top of the stack loses its bond and starts to shift, especially on the side facing prevailing weather.

That is why a rebuild of the upper section usually includes a properly built crown, a cap and new flashing, and why repointing and crown repair done early can prevent the loose-stack stage altogether. Water draining poorly at the base of an exterior chimney can do the same thing to the soil under the footing, so gutters and grading near the chimney deserve a look too.

Next step

Every visit starts with an assessment, and you receive findings with photos before any repair is scheduled. If you are seeing any of the urgent signs above, stop using the fireplace and connected appliances and keep the area below the chimney clear. Then request service; a team member will contact you to confirm a time.

Questions homeowners ask

Sources

1. InterNACHI: Chimney Inspection, Preventing Collapse
2. CSIA: The Three Levels of Chimney Inspections
3. Brick Industry Association: Technical Note 46, Maintenance of Brick Masonry
4. US Consumer Product Safety Commission: Carbon Monoxide Information Center

This guide is general information. It can't diagnose a specific chimney; an inspection can.