Interior garage floor!

[engr567]

Does an interior garage floor slab - concrete slab on grade - need to slope for drainage? Is there any specific requirement on this in ACI? I would appreciate your help.

 

[ToadJones]

Not sure about any ACI provisions, but I do know that:
1). Yes, you should slope it
2). In some localities you are not permitted to have a floor drain unless it is tied to sanitary sewer, NOT storm (which I think is ridiculous).
3). If you are in a cold/snow area and are required to slope the floor out towards the garage door (floor drain not permitted), be prepared to have your garage door freeze shut and tear the weather stripping off when you open it!!!!

 

[engr567]

ToadJones, thank you. Do you know if IBC or any code talk about this requirement?

 

[ToadJones]

My only experience with it was local building codes (counties) when building residential homes. Some counties/municipal building codes had a provision for it, and some did not. I guess you might be best checking local codes.

My preference was always to slope the floor to the center of each bay and install a drain in the center. This drain was then run to the same location as the downspout roof drains....or storm sewer. Many places do not allow this because of potential contaminants from the garage floor. However, I can see no difference between my truck leaking gas on my garage floor and making it into the storm sewer vs. my truck leaking gas directly onto the road!
I guess there needs to be such rules to keep people from doing foolish things like pouring motor oil into their garage floor drain.

 

[cvg]

sending a gallon of used motor oil down the sanitary sewer to the treatment plant is not really a good option either. The typical way this is handled in an industrial or commercial setting is to install an oil/water separator or a grease trap.

 

[ToadJones]

Well, good luck getting contractors to install a oil separator in residential garage!
Point well take though...

 

[MiketheEngineer]

Also there was the theory that gasoline fumes would run downhill and out the door (or pass the loosely fitting gasket)... At least that was what I was taught.

Most cities in this area (StL) want about a 2'' drop in 20' or so.

 

[msquared48]

Also, frequently water heaters are in the garage. If one leaks, it's good to have the slab sloped so the water runs out the garage door, not into the crawlspace, into the house, or just sit there.

Some like to wash their garage floors too. Same idea.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[wannabeSE]

Seismicpe,
See 2006 IBC 406.2.6. The code requires that the floor be sloped to drain or main entrance, but it doesn't specify a minimum slope.

 

[ToadJones]

again, I just caution that if you are in a cold weather area with snow, don't just simply slope the floor to run out the garage door.

 

[Splitrings]

I think typically an 1/8"-1/4" per foot is used on garage floors, with an 1/8" being more typical. I recently used a 1/4" per foot on a 36' deep garage because the landowner wanted to be certain it would drain. Now that the slab is in place it appears 1/4" per foot on such a deep garage is probably a bit excessive. Maybe in shorter lengths 1/4" would be ideal.

Other considerations; seal the floor, use individual drains under each vehicle if at all possible, especially in cold snowy areas, use insulation and/or vapor barrier under slab especially if it is a higher end type garage, we even have people installing radiant heat in garage slabs.

 

[engr567]

thanks all.