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Minimum Floor Slope for Drainage

radioatlas

radioatlas

Registered User
Joined
Sep 27, 2018
Messages
25
Location
North Carolina
Where I'm from, we've always used 1/4" per foot slope for floor slab drainage as is recommended by the ACI. Does the IBC, plumbing code, or any other model code dictate what the actual minimum floor slope is for drainage? Example: IBC 412.3.3 states: "Floors shall be graded and drained to prevent water or fuel from remaining on the floor."
 
Ok maybe that is why my marbles roll down,, in my office?

What year IBC?? IBC 412.3.3

ok 2021 for aircraft hanger

Normally chap 4 is specific to something
 
I've thought at least 1/8" per foot. Not more than 1/4" per foot. I think minimum for "flat" roof is 1/8" and iirc same for roof drains. Seems no hard code guidance (maybe showers?)
 
Thanks to all for replies. North Carolina Building Code (based on IBC 2018). Interior application for an airport hangar. Can't find any actual hard guidance in the code as to what the minimum slope is to achieve "prevent water or fuel from remaining on the floor." Would less than 1/8" be acceptable?
 
Irc

The building code requires that a garage floor be sloped towards the door, but does not specify a minimum slope. It is usually 1/8” to 1/4” per foot. Here is the citation from the International Residential Code (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."

GarageFloorSlope.jpg
 
The building code does not define all situations. When it does not then it is left to the discretion of the designer.
 
The building code does not define all situations. When it does not then it is left to the discretion of the AHJ.
 
Be very careful what you ask for. If the the AHJ decides when the code does not require then the AHJ, and I argue the building official, will have liability for all problems that the owner has with the design. This fits in very nicely with an exemption to governmental immunity.

We live in a system of laws. To give the AHJ the authority to impose requirements not required by properly adopted laws is incompatible with our system of laws.
 
Oh but there is a law. It's a code that states that the floor shall slope to a drain or the door. So as a building official I should blindly accept whatever is presented? A few thousands of an inch can be proven to slope towards a door.
 
Most concrete contractors can do a 1/8" per foot slope with only a few birdbaths. Only the best concrete finishers can do much less of a slope without birdbaths.

On the other hand, most corporate hangars are kept spotless, so any water or fuel is likely to get cleaned up right away.
 
radioatlas said:
Thanks to all for replies. North Carolina Building Code (based on IBC 2018). Interior application for an airport hangar. Can't find any actual hard guidance in the code as to what the minimum slope is to achieve "prevent water or fuel from remaining on the floor." Would less than 1/8" be acceptable?
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Well, there's a lot of subjective judgement imbedded into the word "remain".
Water has surface tension, and the ability for it to move depends not only on slope but also the texture of the floor surface.

Also, if a floor is moist, does that mean water has "remained"? In the roofing industry, the definition of ponding is determined by water remaining after 48 hours.

Is the goal to prevent slips and falls? There are plenty of floor systems that can maintain a DCOF when wet.
 
Yikes said:
Well, there's a lot of subjective judgement imbedded into the word "remain".
Water has surface tension, and the ability for it to move depends not only on slope but also the texture of the floor surface.

Also, if a floor is moist, does that mean water has "remained"? In the roofing industry, the definition of ponding is determined by water remaining after 48 hours.

Is the goal to prevent slips and falls? There are plenty of floor systems that can maintain a DCOF when wet.
Click to expand...
May also be concerned about mold buildup too?
 
Often walkways around buildings are designed with 1-2% cross-slope to encourage water to drain away from the building. Also on large slabs there are usually saw-cuts or "breaks" every 10ft (or more) and those can be designed to help encourage proper drainage. The designer designs, the AHJ approves. It's not a pissing contest.
 
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