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Air Ducts in Slabs-on-Grade ?

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My post, way back whenever, probably involved ducts embedded within
elevated, structural concrete floor slabs.  I have never heard of air ducts
being cast into slabs-on-grade.   It seems to me that the types of problems
that you are now experiencing could have been predicted by any competent
structural engineer, even back in 1950.  Then again, single family homes
didn't usually involve engineers back then, and very few do today.  Texas
state law still does not require such homes to be designed by licenses
professional engineers.  Our firm does not, and will not, do any residential

Now then, my specific answers to your questions are:

1]	No.

2]	I recommend that you fill all of the voids 100% with high strength
grout.  This can be done by pumping.

3]	This probably varies from company to company.  Have your lawyer read
your insurance policy.  Perhaps you can hit the jackpot ... are there any
signs of mold? <grin>

I am forwarding this correspondence to the SEAINT Listserv.  Perhaps one of
the 20,000 other subscribers can help you.  You can monitor the responses
without subscribing by searching through the living archives at

Good luck!

Stan R. Caldwell, P.E., F.ASCE
Vice President
Halff Associates, Inc.
8616 Northwest Plaza Drive
Dallas, Texas  75225
Phone:  (214) 346-6280
Fax:  (214) 739-0095
Email:  scaldwell(--nospam--at)

-----Original Message-----
From: Ken Schaefer [mailto:kens(--nospam--at)]
Sent: Monday, January 28, 2002 4:00 PM
To: scaldwell(--nospam--at)
Subject: in slab ducts

While doing some searching on the internet, I came across bulletin
board in which you had responded to someone asking questions about
in-slab ducts.  If I'm mistaken, my apologies and just let me know.

If not, I've got a couple questions for you.  I have a home in Fort
Worth built in the 1950s.  Each room has at least two air returns
along the baseboards.  All of the air returns, run through the slab.
Evidently, they were some type of box form as there is nothing but
concrete on all four walls of ductwork.

We've had piers (18 ft deep) placed around the entire perimeter of
the home to stabilize some movement.  In spite of this, there are
evidently cracks in the slab the run all the way into the ducts.
During heavy rains, this allows rain water to flow into the ducts.

My questions to you are:

1) Have you seen this problem before?

2)  If so, can it be suitably resolved by sealing off all of the air
returns (without filling the duct cavity with concrete or other
material) and creating new in-ceiling air returns through out the

3) If in fact you are able to comment on any of this, might you have
experience as to whether Insurance companies cover this type of
structural failure?

Thanks for you assistance.

Ken Schaefer
Blanchard Schaefer Advertising and Public Relations
1112 East Copeland  Suite 310
Arlington, TX  76011
Fax 817.860.2004

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