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RE: Flatness Tolerances for Residential Slab

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The way it is supposed to work is by requiring compliance to ACI 117 which is where concrete tolerances are invoked.  The IBC and other buildings codes invoke ACI 318 which invokes ACI 301, but both of these are strictly for structural concrete.  A slab on grade is NOT structural concrete.  ACI 117 is only invoked if you require compliance in the specifications.  


A back door is the phrase "in a professional workmanlike manner" or some other leap of faith specification statement.  Ideally, you should invoke ACI 117 in your specifications.  Most canned specifications do invoke ACI 117.  In construction disputes, I point out that ACI 117 is the only place that defines a "standard of care".  I challenge contractors to come up with any other published document to define "standard of care" for concrete tolerances.


Now after all of that, there is a section in ACI 117 that specifically deals with slabs on grade (ACI Sect.  There is a separate section (ACI 117 Sect 4.5.6) on the flatness and levelness tolerances (FL and FF numbers) per ASTM E1155.  There is a lot of confusion on the topic.  I would advise that you read the commentary on how they define the tolerances.  I always advise engineers to thoroughly read ACI 117 and the commentary.  That is a major area for liability.  If you have specified no tolerances, they could legally build a 20% grade in a "flat" slab on grade. 


Good luck.

Harold O. Sprague

-----Original Message-----
From: Bill Polhemus [mailto:bill(--nospam--at)]
Sent: Thursday, October 16, 2003 9:15 PM
To: aec-residential(--nospam--at);
Subject: Q: Flatness Tolerances for Residential Slab


Although I'm willing to do my own research, I thought I'd try the lazy man's way, and ask here:


What are the governing standards one can cite for the flatness of a residential slab on grade foundation?


Is there anything specific in IBC/IRC? Or would ACI be the place to go?


I've got a residential slab foundation that varies more than 3" in elevation between high and low, has "canyons" and saddleback ridges, etc. I need to know how to ding the contractor for this, chapter and verse.



William L. Polhemus, Jr. P.E.

Polhemus Engineering Company

Katy, Texas USA