Brooklyn chimney collapse (C) Daniel Friedman Inspection for Damage at the Top of Masonry Chimneys, Antennas on Chimneys

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This article describes chimney defects and hazards that can be observed from on-roof access, including damage to a masonry chimney top, antennas mounted on chimneys, shared flues, damaged or missing chimney cap, damaged chimney flue, creosote hazards, & angled chimney flue hazards.

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Damage Inspection at the Top of Masonry Chimneys

Brooklyn chimney collapse (C) Daniel Friedman

A good rain cap or chimney cap (DF's terms) does more than keep out the rain; it also improves chimney draft and prevents downdrafts inside the chimney in windy conditions.

A masonry rain cap such as the one shown in our photo at left can be an effective chimney shelter if it extends past the sides of the chimney and if it is secure.

The chimney shown is a single-wythe flue in Brooklyn, NY. The above-roof section is about to collapse - the chimney is unsafe.

[Click to enlarge any image]

We discuss repairs to chimneys at the roof top at CHIMNEY REPAIRS, TOP & CLAY FLUE TILE.

Other photos and examples of chimney top damage at masonry chimneys can be found at CHIMNEY CAP & CROWN

Photograph of a brick chimney missing bricks, no cap. Photograph of a brick chimney missing bricks, no cap.

Our photos above show two unsafe chimneys that were still in active use. Notice those missing bricks and lost mortar? Damaged chimney top masonry such as missing bricks and a missing chimney cap were easily spotted from ground level at both the Coolidge Hotel in Vermont (above left) and the private home in New York (above right).

The home inspector or owner should ask, "Where did those bricks go? are they blocking the flue? Is the flue damaged and unsafe? What repairs are needed before we install a chimney rain cap?" This chimney may be too short as well - tough to call from ground level.

See Chimney Collapse Hazards & Chimney Support & Bracing Requirements. We discuss repairs to chimneys at the roof top at CHIMNEY REPAIRS, TOP & CLAY FLUE TILE.

Photograph of a cracked chimney top crown and no cap installed.

Our photo shows a chimney with a cracked, damaged, leaky top seal or "crown" and missing rain cap on the flue.

This chimney needs repairs to its top seal and also it needs a rain cap.

Various experts have proposed design details to avoid cracking at the flue liner/concrete interface at the chimney top.

Inspecting homes in both cold and hot climates, wherever we've seen chimney top damage of the sort shown here, it was traced to water (or frost) and not to the absence of a magic expansion gasket.

[Click to enlarge any image]

Chimney used as antenna mount (C) Carson Dunlop Associates

Antennas on chimneys: We also find chimneys used as a mounting spot for antennas or other equipment. Chimneys are not intended to function as a support for other building components.

Mounting an antenna on a chimney may damage the chimney making it unsafe or causing building leaks. You're also inviting a lightning strike on your chimney by mounting equipment there.

A lightning strike on a chimney can cause severe damage to a home, including setting it on fire. Some readers have reported just that happening to their home. Sketch courtesy of Carson Dunlop.

Obstructed or Blocked Chimney Flues

Photograph of chimney partly blocked by an insect nest of hornets.

Obstructed or Blocked Chimney Flues might be discovered by inspection and luck as shown here.

A hornets nest is partly blocking this flue. Not only may there be a chimney safety or performance problem, there could be a problem for the inspector or the building occupants when the hornets are disturbed.

A meticulous chimney mason would also criticize the mason who built this chimney for leaving oozed mortar sticking into the flue between each pair of flue tile liners.

That detail can make a chimney hard to clean and can make for damage and flue leaks if the mortar "ears" are broken off during chimney cleaning.
We were able to take this clever photo of a dark chimney interior by using our Maglite™ flashlight along with a Nikon Coolpix 4500™ camera on which we re-set the ISO or equivalent film speed to its highest setting (800). This trick with a digital camera will sometimes let an inspector "see" into a pretty dark area.

Clay flue tile liners mitered when on angle (C) Carson Dunlop Associates

Angled Flue Tiles

Just as we reported that a clay tile lined chimney would be difficult to clean due to projecting concrete between vertically-stacked clay chimney tiles, clay tiles need to be cut properly when constructing an angled chimney such as the one shown in Carson Dunlop's sketch.

Only the bottom design, showing that the clay chimney tile was cut on an angle, is correct. The top two designs risk both cleaning difficulties and also water, smoke, soot,or creosote leaks into the chimney structure.

Details are at Angled Chimney Flues

Determine the Extent of Chimney Damage and the Safety of the Entire Chimney Flue

First, you will want to be absolutely sure that the chimney damage, whether to the ceramic clay flue liner or to the surrounding masonry or both, is limited to the upper, visible, accessible part of the chimney.

Other chimney damage lower in the chimney itself as it passes through or alongside the building could be very dangerous, even fatal if carbon monoxide or other flue gases leak into the building or if sparks cause a fire.

We suggest that you hire a professional chimney sweep who can examine the entire flue. Most chimney sweeps also offer repair services, and can suggest what repairs are needed and give alternatives for the particular chimney and flue on your building.

We discuss repairs to chimneys at the roof top at CHIMNEY REPAIRS, TOP & CLAY FLUE TILE.

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