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3/8" ACCEPTABLE TOLERANCE ON CONCRETE? 3

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structurebeton

structurebeton

Structural
Apr 24, 2003
88
A residential contractor is telling me that 3/8" differential for a 32" distance on concrete is an acceptable construction tolerance. Where would he come up with something like that? Can someone point me which standard he could be referring to? He claims his concrete floor can have that much diferential and it is still an adequate construction.
 
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That sounds like it is just sloppy work. If it is a slab, how big is the slab? Is it just a footing?

Ask him where it shows it is acceptable.

I haven't looked at the ACI or codes, but they should have the answer. What do your specs say?

Dick
 
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ACI has tolerances listed in their publications.
 
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It is a basement slab, with walls bearing directly over the slab. Some floors are not level on the 2nd story. The contractor claims it is because the concrete is not level, but still within concrete floor tolerances...Slab level tolerance used to be 1/8" on a 10ft distance according to the contractor's guide to quality concrete construction.

I was just wondering if any has seen other references for concrete tolerance for floor slabs.
 
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ACI 117-06. But I think it only applies if referenced in your Specs.
 
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I did not specify anything for this project. This is an existing new house (18 months old) which I was called to evaluate the cause of floor unlevelness.
 
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The normal standard of construction for a slab is 1/8" in 10 feet, but this could be hard to enforce if there was nothing in the specs about it.

Needless to say that this slab is a little out of standard, just a little. Like 12 times +-.

Mike McCann
MMC Engineering
 
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How much is the second floor out of level?

If the slab is not cracked, there probably is not settlement there, but just the surface variation. Since the first and second floor were framed on the slab there was either no corrections made during construction or there was additional settlement or shrinkage. If there is just one 3/8" variation in the foundation slab, you could not expects this to telegraph up to the second floor, but would be distributed in a larger general area.

It does not seem logical that a 3/8" slab variation would cause a major settlement in a structural apparently built to standards unless there were other factors that caused an owner to hire an engineer on a hunt for a single probable cause. - Is the owner in a conflict with the builder over other issues?

Dick
 
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ACI 117 provides 1/2" in 10-feet for conventional floors. This is the basically the minimum acceptable. The 1/8" noted above is for superflat designated floors and shouln't be applicable to residential concrete unless specified. Please do not try to evaluate on anything other than a standard 10-foot straight edge or floor flatness measurements, it really muddies the waters when trying to argue without referencing standardized tolerance measurements.

If you could get a peak at the IRC code, there may be additional guidance in there for you on this.

Greg
 
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There are two means of accepted measurement of floor flatness and level. The "f-number" concept uses a single number to depict the floor flatness (ff) and levelness (fl), with criteria ranging from equivalence to the older reference of 1/8" in 10 feet, to "superflat" conditions. The "f-numbers" are based on measurement with a Face Floor Profiler, commonly called a "dipstick".

As others have noted, 1/8" in 10 feet is a common tolerance and achievable without much difficulty. The noted 3/8" in 32" is absurdly bad construction for a floor slab. Chairs won't sit flat, tables will rock, people will stumble.

 
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Ron,
1/8 in. in 10 ft is a common tolerance only because it was in use for many years when no one measured floors, and is now in use because some specifiers don't understand floor flatness. And it definitely is not "achievable without much difficulty," especially for residential construction. In fact, ACI 117-06 doesn't even include that tolerance. The tightest straightedge tolerance in ACI 117-06 is 3/8 in. in 10 ft for 100% compliance. There is virtually no need for a residential floor that is flat to within 1/8 in. in 10 ft or with an FF number of 60, the superflat category. As stated in ACI 117-06, "Only skilled contractors, using sophisticated equipment, will be able to achieve this level of quality." That level of quality is specified for high-rack warehouses, TV studios, or other floors that must be superflat to perform well.
 
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For residential, some codes require a slope to 'sump' for basement floors.

Dik
 
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Is the construction going to use tiled flooring? Maybe, just maybe, the contractor is arguing that structurally there is no problem and the differntial may be built out by the bedding for the floor tile. This is typically done here in Asia from what I see (including my condo in Thailand . . . arggggg).
 
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BihH -

The grout or second pour of low strength concrete is also common in India where the "wet rooms" (kitchens, entries, bathroom, showers)in a home where the floors are tile. Additionally, there they also have the dual waste situation where they have "gray" and "black" water separated.

I think in this case, the 3/8" variation on the basement floor slab is being looked at as a the possible cause of settlement on the second floor (unless I missed something).

Dick
 
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concretedoc...I'm aware of the application of 1/8" in 10 feet tolerances. No, it isn't required in residential construction; however, residential concrete construction is generally miserable and about anything a contractor can do to adulterate the concrete and its finish gets done.

1/8" in 10 feet isn't anywhere near an Ff of 60...that requires extraordinary techniques, attention to mix design characteristics and skilled craftsmen. With a little skill and readily available tools, 1/8" in 10 feet is achievable, but you can't start with a slump of 6 inches then add water to get it even higher and expect to achieve that tolerance and a durable finish.

My whole point is that 3/8" in 32" is deplorable concrete construction and should be rejected, residential or not.
 
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The argument that the concrete floor in the basement is causing the sloping in the the 2nd floor is bogus because the 1st floor is not as bad as the 2nd floor, therefore, the sloping in the 2nd floor is caused by structural framing problems, such as undersized floor joists to support the walls...

I just wanted to know if the argument of an 3/8" concrete differential is an argument that can be thrown out right off the batt.
 
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Regarding the tolerance - "Standards" such as this are often enumerated in a publication that is authored by the Home Builders Association. Needless to say, they tend to be somewhat generous toward the home builder.
With that said, it is likely that any agreement between the builder and the homeowner has some language referring to HBA standards as the measure that applies.
It might be "sloppy" and it might not conform to anything by ACI, but it is likely to be the legal standard that applies in this situation.

 
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The builder needs to go by IRC2006 which is state mandated. IRC refers to ACI. How can the HBA standards be less than IRC/ACI?
 
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