INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# Floor slope

## Floor slope

(OP)
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?

### RE: Floor slope

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.

### RE: Floor slope

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

### RE: Floor slope

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.

### RE: Floor slope

(OP)
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.

### RE: Floor slope

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

### RE: Floor slope

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

### RE: Floor slope

(OP)
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.

### RE: Floor slope

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.

### RE: Floor slope

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.

### RE: Floor slope

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.

### RE: Floor slope

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. ### RE: Floor slope 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 ### RE: Floor slope 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. ### RE: Floor slope 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. ### RE: Floor slope 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. ### RE: Floor slope (OP) 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. ### RE: Floor slope 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. ### RE: Floor slope #### Quote: 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 ### RE: Floor slope RE...you're right...left out a conversion factor. Mea Culpa ### RE: Floor slope No problems Ron, had to make sure because I put a slope in all my garages, normally 1:200 (this way it can be converted to a room in the future if the need arises with minimal$). Don't know what that is in inches per foot, but I have never had a complaint about extra moneys.

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

### RE: Floor slope

1:200 is very close to 1/16" per foot.

BA

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!