Case of the Month: The Fallen Flue

Jan 1, 2015 by

The insured owned an unoccupied, three-story rental mountain “cabin”. A second-story chimney fell, hitting the guardrail of a balcony located over the garage. This reportedly allowed water into the roof of the garage, which caused significant drywall and framing damage. The insured said the chimney fell as a result of wind. The client thought that the cause was snow load. GEI was assigned to determine the cause and approximate age of the water damage.

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The building was a single-family home of wood frame construction on a steep slope. The roof consisted of sheet metal on plywood sheathing. The exterior walls were 2 by 4 framing with exterior plywood sheathing on the outside and sheetrock on the inside. The foundation consisted of conventional concrete spread footings. Some snow still remained on the ground and on the balcony at the time of our inspection.

The chimney that fell onto the balcony deck and damaged the guardrail was a metal fireplace flue that was 10 inches in diameter and 7 feet long. The weight of the flue, along with the components that fell with it, was about 190 pounds, or the weight of a reasonable size male adult.
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The chimney fell off the furnace and onto the balcony. This was reported to be due to some combination of high winds and excessive snow loads. The possibility that the wind alone launched the chimney into the guardrail was considered. This was dismissed because, short of a tornado, wind forces do not launch the equivalent of a 190-pound man. It was presumed that once the chimney fell, it then slid approximately 12 inches and came to rest against the steel framed portion of the guardrail. The slide of the chimney was likely assisted by the snow accumulation on the balcony, which sloped towards the balcony guardrail. Some sections of the balcony guardrail were wood framed and some were steel framed.

The steel framed portion of the balcony guardrail was leaning outward, and the broken post mounting surface allowed water into the balcony framing that the guardrail was bolted onto.

Shifting our attention to the chimney, lag bolts of different lengths connected the chimney steel straps to the roof framing before the fall occurred. This lag bolt non-uniformity was evidence of a faulty installation.

Also, there was water damage to the roof plywood sheathing where the chimney mounting straps had been attached to the roof sheathing. This led to a reduction in the holding capacity of the wood and corrosion of the lag bolts. The long-term intrusion of water and deterioration of the sheathing in the area of the bolts contributed to the fall of the chimney.

Both welds that connected one of the steel straps to the chimney had been severed before the collapse, as evidenced by the significant amount of corrosion present on the sheared faces of the welds. The fall of the chimney was the result of a combination of construction and maintenance issues.

The outward tilting steel guardrail mounting posts damaged the balcony waterproofing immediately around the posts. This then allowed water to enter and deteriorate the balcony floor/garage roof framing. Paint was chipped off of a small area of the steel framed portion of the balcony guardrail, where the chimney struck it. This was a recent event. Although paint had been chipped off, there was no kinking in the steel surface that would be consistent with a damaging impact. In addition, there was no paint transfer from the guardrail to the chimney. This indicated that the impact was minor.

Our expert computed the horizontal thrust that the balcony guardrail would be required to resist to be in compliance with the California Building Code as 320 pounds. The horizontal thrust, due to the impact of the chimney was determined to be 88 pounds. These computations demonstrated what was intuitively apparent. A man, or the equivalent thereof, leaning on, or even running into, an adequately constructed balcony guardrail would not cause it to fail.

There was also a separation between the wood framed portion of the guardrail facing east and the wood framed guardrail facing north. This separation was not the result of the chimney impact. The ends of the balusters were painted over indicating the gap was present and pronounced at the time the guardrail was last painted.

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The base of the balcony guardrail was observed through the garage ceiling. One of the two lag bolts that connected the guardrail post to the garage wall framing was missing. It was this deficiency that was the principal cause of the outward tilting of the balcony guardrail.

In summary:

· The chimney did not fall due to either wind or snow load. It fell because its mounting bolts and straps were corroded and inadequate.

· The wood framed handrail had already separated before the last time that it was painted.

· The steel handrail base was not significantly damaged by the falling chimney.

· The steel handrail base was leaking water due to lack of maintenance for at least three months before the chimney fell.

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