Thread: levelness of slab on grade foundation

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.

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Originally Posted by Gary Mohel

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]

Originally Posted by Gary Mohel

I've heard 1" in 20' is alright on new construction but I have no idea where that comes from.

El concreto finisher

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.

"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.

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 . . .

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!

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

Originally Posted by Matt Fellman

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!