Brick Veneer,
Metal Studs and Smashed Cars
In the early 80's somewhere in Texas
(I believe Houston) a whole section
of brick veneer fell from the
exterior of a high rise building
literally smashing a parked car
below. This incident was the first
indication that the marriage of
brick veneer and metal stud wall
construction was going to be a major
problem in high rise construction.
What led to this disaster? The chain
of small failures that led to the
major failure are logical and
fascinating. The chronology and key
contributing factors are as follows:
1.) Wind and Barometric Pressure:
When we enter a very tall building
you will often hear the low howl and
feel the rush of air into or out of
the building. Changes in barometric
pressure cause an imbalance between
internal and external pressure in
large buildings that takes a while
to equalize.
2.) An inflexible veneer over a
flexible structure: When you put a
brittle brick veneer system over a
flexible steel stud structure,
something's got to give - the wrong
thing.
Wind and quick changes in barometric
pressure exerted considerable forces
upon the wall envelope of the
building. This constant in and out
flexing caused the bond between
mortar and brick in bed joints to
fail. The resulting hairline cracks
went un-noticed and no one would
have imagined this as the beginning
of catastrophic failure.
3.) Moisture Intrusion: Unequal
barometric pressure within and
without of large buildings casts a
whole new light on moisture
intrusion forensics. Negative
internal pressure can literally draw
moisture into the cracks and
crevices of a building by the gallon
and did.
4.) Corrosion: Wet steel rusts and
corrodes away. These last two
factors sealed the fate of a system
that appeared to be well thought
out. Negative building pressure
literally sucked water in through
the failed bed joints. This in turn
was wetting the anchorage system.
Although the metal studs and the
wall ties were galvanized steel, the
self-tapping screws through the
studs exposed raw unprotected steel.
Eventually the steel stud around the
anchorage fastening screw failed.
Finally, high wind or extreme
pressure caused whole sections of
the brick veneer to literally fall
out of the wall to the street below.
