Minimum slope to drain a parking lot.
Minimum slope to drain a parking lot.
(OP)
I am constructing 2 buildings with a driveway and parking lot inbetween each building.
I am in Moore Oklahoma.
My buildings are 300' by 60'. My concrete drive and parking spaces are 70' between buildings.
I have a gabled roof on each building I am draining 30' of run off per building or a total of 60' of roof run off in a 70' parking lot. ie 130' total run off.
I am taking the water to the street. So at the back of the parking lot in the center I am planning on sitting my valley 8" below the floor level of each building.
My question is what is the absolute minimum that I can set the flow line grade?
Concrete people say 1 foot per 100 (1%). So at the front of my building my "V" in the driveway would be 3 feet 8 inches making the parking slope pretty steep.
I am sure there is math to figure this out. Everyone says if you don't have this 1% slope the water will not drain. If I put in a .5% slope I would have 26 inches of fall at the front. I don't see how a driving wind can hold back a wall of water 26 inches tall to flood buildings.
Any help is greatly appreciated.
Thanks
I am in Moore Oklahoma.
My buildings are 300' by 60'. My concrete drive and parking spaces are 70' between buildings.
I have a gabled roof on each building I am draining 30' of run off per building or a total of 60' of roof run off in a 70' parking lot. ie 130' total run off.
I am taking the water to the street. So at the back of the parking lot in the center I am planning on sitting my valley 8" below the floor level of each building.
My question is what is the absolute minimum that I can set the flow line grade?
Concrete people say 1 foot per 100 (1%). So at the front of my building my "V" in the driveway would be 3 feet 8 inches making the parking slope pretty steep.
I am sure there is math to figure this out. Everyone says if you don't have this 1% slope the water will not drain. If I put in a .5% slope I would have 26 inches of fall at the front. I don't see how a driving wind can hold back a wall of water 26 inches tall to flood buildings.
Any help is greatly appreciated.
Thanks





RE: Minimum slope to drain a parking lot.
Professional and Structural Engineer (ME, NH)
American Concrete Industries
www.americanconcrete.com
RE: Minimum slope to drain a parking lot.
RE: Minimum slope to drain a parking lot.
There might be local codes that dictate minimum slopes. Further,assuming you are in the US, you have ADA requirements that must be met as well. Not as simple as you might assume....additionally, if you obtained a permit based on a particular civil drainage plan, changing that might require a permit revision.
RE: Minimum slope to drain a parking lot.
Is this a concrete slab? Usually parking lots are in Asphalt. In either case, I have always maintained 1% for the finished grade and as little as 0.5% for the piping depending on the minimums allowed.
Ron: I think he is in Moore (or less) Oklahoma. Kinda flat there???
Mike McCann, PE, SE (WA)
RE: Minimum slope to drain a parking lot.
Long day of deposition....still cranky!
Yes, Mike's advice is good; however, the project civil engineer should have shown this on your plans. It isn't whether a wind will hold back that amount of water for a backup, but how fast the water gets to its exit point and the ability of the exit point to handle that amount of water quickly.
A parking lot will drain at 0.5 percent slope. If you are putting in an asphalt parking lot, not a big deal. If concrete, this slower movement of water can affect the joints in the concrete, so make sure they are sealed properly.
RE: Minimum slope to drain a parking lot.
Yes it is a concrete drive.
There is no drainage retention on the lot. We drain to the street and at the bottom of the drive 3/4 mile away there is a huge pond that serves as retention for the sub division. So the drainage flows directly out of the parking lot down the approach and to the gutter curb.
CVG: What is the 100 year flood level statement. I do not know what the level is. I am more or less at the top of a slope, no one drains on me, I am probably 50 feet above the overflow of the pond down the street. I don't see how I could possibly flood unless I pour a concrete drive just inches below the floor grade. I see parking lots, Walmart, Lowes ect much larger than mine with almost no slope to their drainage ares.
Ron: "Further,assuming you are in the US, you have ADA requirement." Yes I am in the US, and ADA is a pain in the rear and that is one reason why the question is asked. If a ADA parking spot is located at the front, you will need a elevator to lift the car to the spot if it is poured on a 1% slope.
My plan is to put the ADA spot about halfway down the buildings.
RE: Minimum slope to drain a parking lot.