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Brick Veneer, Metal Studs and Smashed Cars


mgbinspect
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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.

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In large high rise buildings it's not so much a barometric pressure problem as it is a stack (chimney) effect. The elevator shafts are the worse for creating the updraft effect. This is why a lot of the high rise buildings are in a negative pressure. Now with the advent of electronic controls they are able to place static pressure sensors on each floor as well as outside. The building automation control scheme will average the sensors on all the floors, measure the pressure outside and then control the amount of outside air that the air handler(s) bring in to compensate. These air handlers are also VAV (variable air volume)which can change the amount of air delivered based on static pressure needs.

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  • 3 years later...

Mike, On your write up. Will you go into more details on mortar IE high lime and brake down the types of mortar Type N and so on.

Thanks

Erik

Hi Eric. This is about a 3 year old thread. I'm not sure MGBInspect has been around in here much in the last couple years.

It is a pretty good write up, though.

Good questions on the Type N vs. High Lime Mortar.

You might want to just google up up any of the DeGruchy sites and read up, or the US Heritage Group in Chicago.

http://www.usheritage.com

or

http://www.degruchymasonry.com

Degruchy is remarkable. US Heritage has an excellent matching service.

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Kurt, Thanks for the links. I really have appreciated what you guys have shared on the forum. I really fill it has helped me. Not only what I have learned off the old post. But it has taken my reports to the next level. I can find things here I haven't been able to before.

Thanks,

Erik

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Kurt, I gotta tell you, I LOVE your avatar! And, at 58, I can tell you that picture was me at about maybe 4 years old. I can assure you that's something you only do once - far more affective than child protectors. I remember that experience to this day as vividly as if it happened yesterday. Yoddi... yadda.... Lol...

Golly, while I have been gone for a year or so I already feel the guilt of having drifted from the topic. Shame on me! Don't reply to this latest comment. It's all coming back to me now...

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