Concrete slab flatness standards

Bearded Wonder

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Joined Jan 21, 2011

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Discussion starter · #1 · Apr 20, 2016

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We were talking yesterday at the office and the topic came up of what is the reasonable amount of tolerance for a residential slab as far as flatness? Seems like when I was a superintendent for a company years ago, they said it could vary up to 1" over the entire slab, and no more than 1/2" in any 10, and they considered that "flat", which seems pretty loose to me.

Is there some general standard that I'm not aware of? I know generally there is some variation across a slab even with a good Concrete crew, but what is an acceptable amount?

Thx.

 

asevereid

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Joined Jan 30, 2012

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#2 · Apr 20, 2016 (Edited)

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I'm not aware of any requirements for the finishing/flatwork crews , but the NWFA and TCNA have their own requirements for slab flatness.
I think the NWFA requires less than 3/16 or 1/8 deviation in 10'?

I know the restaurant I was just working at had a deviation of 5/8 over 6'....right where a 16' long walnut slab table had to be installed... With legs that had very little adjustability... SUNUVABITCH!

 

9

91782

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#3 · Apr 20, 2016

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Residential you say? Whew!

Man "flatness" standards are many and varied and complex.

3/8" in 32".

I've seen both worse and better.

 

J

jlhaslip

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#4 · Apr 20, 2016

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The concrete guy I use drops a quarter into water collecting in the low spot and expects a dry side.

 

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91782

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#5 · Apr 21, 2016

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SmallTownGuy said:

Residential you say? Whew!

Man "flatness" standards are many and varied and complex.

3/8" in 32".

I've seen both worse and better.

Click to expand...

Might as well get the NAHB book on standards:

https://builderbooks.com

https://builderbooks.com/media/flip...edia/flippingbook/pdf/rcpg_4e__contractor/r/c/rcpg_4th_ed-contractor_final4.pdf

page 5:
--------
"Performance Guideline: Except where the floor or portion of the floor has been designed for specific drainage purposes, concrete floors in living areas will not have pits, depressions, or areas of unevenness
exceeding 3/8 inch in 32 inches. (See “Taking Measurements” in the
Introduction for information on 32-inch levels.)"

 

B

builditguy

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#6 · Apr 22, 2016

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I always tell people, there are no low spots. Only high areas.

Or

That's not a low spot. It's so level, it's like a piece of glass. The water has no where to run.