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Gary Mohel
12-30-2009, 04:20 PM
What is proper concerning the levelness of a slab on grade foundation? I've heard 1" in 20' is alright on new construction but I have no idea where that comes from. I haven't located the information in the IRC.

Dan Harris
12-30-2009, 04:52 PM
What is proper concerning the levelness of a slab on grade foundation? I've heard 1" in 20' is alright on new construction but I have no idea where that comes from. I haven't located the information in the IRC.

AZ requirements are 1/4" in 12' I believe thats the same as the NAHIB? [some builders assoc. workmanship requirements]

chris mcintyre
12-30-2009, 06:46 PM
I've heard 1" in 20' is alright on new construction but I have no idea where that comes from.

El concreto finisher :)

John Kogel
12-30-2009, 07:56 PM
The Canadian National Warranty Program max "out of level" on a concrete floor is 1/4" in 32" or max slope of 1/240 times room width. Yeah, that second rule is the same as saying max slope 1" in 20 feet. :)
I would use the first for measuring smaller bumps and dips, 1" in 10.67 feet.

Jerry Peck
12-30-2009, 08:38 PM
"levelness of slab on grade"

versus

"flatness of slab on grade"

I believe what is being discussed really is "flatness", i.e., "in plane" or "out of plane".

One could have a "flat" but "unlevel" slab.

Also to consider is what flooring it to be installed as wood floors require a rather "flat" (in plane) slab.

A.D. Miller
12-31-2009, 04:46 AM
Slabs-on-grade are subject to two tolerances. One is the overall tolerance above and below the specified elevation and the other is the flatness and levelness of the floor finish. Flatness is the degree to which the surface approximates a plane. Levelness is the degree to which the surface parallels the horizontal.

The industry standards are:

ACI 117-90, Standard Tolerances for Concrete Construction and Materials, American Concrete Institute

ASTM E1155-87, Standard Test Method for Determining Floor Flatness and Levelness Unsing the F-Number System, American Society for Testing and Materials

For levelness, the rule of thumb is L/360, or take the length of the concrete slab in inches and divide it by 360, giving you the amount in inches of allowable deflection from level.

For flatness it gets rather complicated in that one must know how the floor was finished, i.e. bullfloated, straightedged, flat, or very flat . . .

Scott Patterson
12-31-2009, 09:46 AM
My rule of thumb is if I can notice that a slab is not level, then it is! If you can see it or feel it then it is. Pretty darn simple if ya ask me! ;)

Matt Fellman
12-31-2009, 06:58 PM
I use the golf ball trick JP talks about....

I just got a great deal on some Tiger Woods balls on Ebay... they came attached to his wife's hand :)

A.D. Miller
01-01-2010, 02:12 PM
I use the golf ball trick JP talks about....

I just got a great deal on some Tiger Woods balls on Ebay... they came attached to his wife's hand :)

MF: oUCH!:eek: