Floor slope

[SteelPE]

I am looking for a provision in a building code (IBC) that would indicate the minimum slope required for a garage floor. Does such a provision exist?

 

[JAE]

No minimum provision that I know of. If you are trying to ensure that water drains, usually a 1/2% slope is sort of a civil engineer's minimum...they usually prefer 1% but "rain doesn't stand on a level surface" either.

 

[woodman88]

The minimum per IBC is in Section 406.1.3 "...The area of floor used for parking of automobiles or other vehicles shall be sloped to facilitate the movement of liquids to a drain or toward the main vehicle entry doorway....". The problem is that there is no easy definition (per the code) of what facilitate means in regard to slope. I will go along with JAE answer.

Garth Dreger PE
AZ Phoenix area

 

[SLTA]

From the IRC, R309.4: "The area of floor used for parking of automobiles or other vehicles shall be sloped to facilitate the movement of liquids to a drain or toward the main vehicle entry doorway."

Agrees with what JAE said.

 

[SteelPE]

Thanks guys, I had already found this provision but I was looking for an actual number. The problem that I have is that there is no code provision that requires you to use the 0.5%. If the architect or owner wants to use a different number, there are no requirements to dispute said number.

 

[BAretired]

It is not a code requirement, but 1/8" per foot is a minimum slope that I have seen specified. That would be close to 1.0%.

Anything flatter than that is liable to disappear if you have expansive clay underlying the slab.

BA

 

[Ron]

Agree with BA...1/8" per foot is minimum slope required to cause drainage.

 

[SteelPE]

Thanks for the help guys. However, I am looking for a code reference. If there is no code reference (other than saying that it must pitch to a drain of the OH door) then that is an acceptable answer. I just want to make sure there is no reference.

 

[steellion]

SteelPE, it's not written in mandatory language, but ACI 362 recommends a minimum of 1.5% slope in any direction, with 2% being preferred for garages.

 

[Ron]

SteelPE...I did a key word search through the 2006 IBC using several different key words (garage floor, floor slope, slope to drain, 1/8" per foot, 1/8" in 12") and came up dry on each. As JAE originally noted...not in there!

A 0.5% slope also as JAE noted, is pretty much the bare minimum (for pavements). A 1/8" per foot is about 1% and will cause positive drainage; although not adequate for critical drainage such as a roof.

It doesn't appear that you have a section to reference, just a general consensus that it should be in that 0.5 to 1 percent range at least.

 

[paddingtongreen]

What is the required flatness of the floor surface. From that you can find the minimum practical to avoid puddles. Other than that, I agree on 1/8" in 12".

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[Ron]

I don't know that anything greater than 1% is really workable. For a typical 20' garage length, at 1% you have a 2-1/2" grade change. A 2% slope would give a 5" grade change...likely not workable. Would increase the cost of a typical 2000 square foot home by about $5000 for fill and compaction.

 

[rowingengineer]

Ron,
Your maths sounds off, because if you didn't grade the fill and just used extra concrete, you would get (20'x20'x (5/12)'/2 )*.333^3(6mx6mx.125m/2)= 3 cubyard (or 2.25cubm)which is about $2000 Max, probably more like $800 on a good day given.

Someone please check my maths this whole feet to yard to inches thing has me in a spin.

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it

 

[Teguci]

Code says the floor has to be sloped (not designed but constructed). Given placed concrete tolerances, anything less than 1/8" per foot can come back to the architect when the contractor builds it dead flat or with occasional puddles. If the Architect wants higher construction tolerances he will need to note that and the owner will have to pay.

 

[paddingtongreen]

Where I come from, the slope has to be shown on the drawing, and therefore, is part of the design. The Contractor won't slope the floor unless the drawing tells him to.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[Teguci]

To rephrase, if the drawings call for less than a 1/8" per foot slope without a specified higher construction tolerance, the resulting puddles, in my opinion, are owned by the Architect.

 

[SteelPE]

In this particular instance the architect does not show anything on the drawings other that the floor must slope in this direction. The code has no direction on how much slope is to be provided. It seems like nobody wants to take responsibility for this number.

 

[paddingtongreen]

As I said earlier, you must look at the flatness tolerance for the floor and slope it so that even the low points can slope toward the drain.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[BAretired]

The code has no direction on how much slope is to be provided. It seems like nobody wants to take responsibility for this number.

The code has no direction on how far apart the floors should be either. Some decisions are left up to the designer.

BA

 

[Ron]

RE...you're right...left out a conversion factor. Mea Culpa