The fallen flue

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 damage reportedly allowed water intrusion into the roof of the first story garage.   The insured said the chimney fell as a result of wind.   The client said that the cause was snow load.   GEI was assigned to inspect the insured’s cabin to identify and determine the cause and approximate age of the damage.

The building was a single-family, three-story home of wood frame construction on a steep slope.   The roof consisted of sheet metal on plywood sheathing.   The exterior walls were of 2x stud construction with exterior plywood sheathing on the outside and gypsum wallboard on the inside.   The foundation consisted of conventional concrete spread footings.   Some snow still remained on the balcony at the time of our inspection.

The chimney that fell onto the balcony deck and impacted the guardrail was found to be 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 193 pounds – the weight of a reasonable size male adult.

The chimney fell off the furnace and onto the balcony.   Determining the cause of this event was not part of this evaluation, but it 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 200-pound man.

It is 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 facilitated by the snow accumulation on the balcony, which sloped towards the balcony guardrail.

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

Lag bolts of different lengths connected the chimney steel straps to the roof framing (prior to the fall).   The lag bolt non-uniformity was evidence of a faulty installation.

We observed water damage to the roof plywood sheathing where the chimney mounting straps had been embedded in the roof sheathing.   This led to a combined 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 connectors contributed to the collapse 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 in the sheared faces of the welds.   The collapse of the chimney was the result of a combination of construction and maintenance issues.

The outward tilting of the steel framed portion of the guardrail intermediate posts damaged the balcony waterproofing immediately around the posts.   This then allowed ambient 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 substantial impact.   In addition, there was no paint transfer from the guardrail to the chimney.   This indicated that, at most, 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.  The computations illustrated 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 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.

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 for the outward tilting of the balcony guardrail.

In conclusion, the primary cause of the distress observed was deficient construction (lag bolts) and maintenance of the structural elements of the balcony guardrail.   This was exacerbated by a combination of snow forces and impact from the fallen chimney.   The distress was likely to have occurred within the last three months before the date of the inspection.

The snow damaged camping lodge

This case involves a summertime campground facility built in 1951, and nestled high in the Sierra Nevada mountains. Over the winter, the camp was inaccessible and as the snow melted and the caretakers returned, they noticed an exterior wall in the main building that was bowed in by several inches.  Eventually GEI was called in for an examination.

Our inspection discovered the following:

  • A portion of the first story exterior wall of the main building had moved and cracked.
  • The exterior stairway to the second floor of the main building had collapsed.
  • The roof structure was sagging.
  • The foundations were cracked.
  • There was dry rot and insect damage at the base of some of the walls.
  • A visit to the attic showed that there had been repairs to the roof structure in the past.
  • The roof ridge beam in the vicinity of the earlier repairs was crushed.
  • Some of the purlins in the roof structure also were broken.
  • Some of the replacement posts in the attic had moved as well.

The next step was an evaluation of the observations.  Starting at the foundations, there had been some soil movement over the past number of years, but it was not serious and was not the prime cause of the observed damages.

The dry rot and insect damage needed repairs, but also had not yet seriously compromised the strength of the walls.

We discovered that there were really two separate issues-the wall and the roof, although both had been damaged by snow.

Researching the snow loads, we found that for the years of 1947 to 2004, the heaviest snowfall was in 1951-1952, with the maximum total annual snowfall of 444 inches.  The greatest total monthly snowfall was in January 1952, and was 127 inches.  We did not have all the data for the current snow season yet, but the incomplete data projected that the maximum total annual snowfall would be 157 inches.  The deepest snowfall was recorded in January with an approximate depth of 70 inches.  This indicated that there were heavier snowfalls prior and/or during the construction of the building.  Also, the retrofit to the roof structure indicated structural problems with the roof structure were recognized and corrected in the past.  We also detected evidence of multiple roofing materials. An excessive load from roofing materials, construction equipment and roofers walking on the roof during re-roofing can also damage a roof structure. Generally a building movement of this nature is caused by excessive or unbalanced snow load on the roof structure, and poor design/construction practices.  In this case, it was not a single event, but the cumulative effect on a roof that was not designed/constructed to take the snow loads that it was annually subjected to.

The issue of the damaged wall was also interesting.  There was another building a few feet away, whose peaked roof shed snow into the walkway between the two buildings.  Over the course of the winter, the snow slid off the roof of the second building and filled up the walkway between the buildings.  A winter caretaker reported that the snow was up to nine feet deep between the two buildings during the winter.  The buildup of packed snow delivered a lateral thrust against the wall, which was never designed to resist such a pressure.  The result was a series of broken 2 by 6 vertical wall studs and a five inch inward deflection in the wall.

The main building was in an eminent collapse mode.   It lost its structural integrity and could not resist any new forces or loads.  The weight of the building itself, more lateral movement in the wall, or a moderate wind/earthquake load would have caused the total collapse of the building.  It was therefore a hazard to the public; and was ‘red tagged” until repairs could be accomplished.

While it was inconvenient for the camp operators to use alternate facilities , our engineer averted disaster by his timely analysis.  If a thunderstorm had occurred while the lodge was filled with little campers, the story would not have had a happy ending.  The protection of the public is a responsibility that our engineers take very seriously.