I’m installing a new asphalt driveway (4″ base, 2″ asphalt) that will run 80 feet in from street, then open into large parking area (55′ x 30′) at the rear of the house. (Please see attached diagram, not to scale.) The driveway will be lined with belgian block throughout, which will eliminate runoff to the sides.
In getting estimates, all paving contractors stated that a drain (cesspool) should be located in front of/near the garage door area to deal with water runoff.
My questions to the pro’s here:
1. Is a drain really recommended? If so, what capacity?
2. I’d prefer that the parking space in front of the garage not acquire the appearance of a “bowl” with a drain in the middle (Circle “A” on the plan.) Can the drain be installed without a dip – flat on flat – and still be effective? If not, what’s the recommended pitch?
3. If the drain is located farther away from the house and garage at spot “B” (see plan) what’s the recommended pitch away from the house?
Any other thoughts or suggestions greatly appreciated. Thanks in advance.
Replies
1. Yes a drain is necessary... water in garage is a bad thing. Is it "always necessary"? No... but more times than not, it is. Capacity? A consult with an engineer is not that expensive if you have all of the drawings, elevations, etc. If you don't want to go that route.. oversize it.
2. Have you thought about a straight drain-grate, all the way across the front of the garage? It looks much better and has a wider margin for error on the grade, as it covers the entire front of the doorway. The "dip" can be relatively small... but without elevations and my asphalt guy sitting right here, I am at a loss to tell you exactly how much. Your asphalt contractor should be able to give you some ideas.
3. I wouldn't do "b". the idea is to have the water flow away from the door. If you do it at that location, te water is flowing in front of the door... and can run inside if the conditions are right.
Edited 8/11/2004 3:15 pm ET by Rich from Columbus
I've got about 15 years in asphalt paving, so I hope I can answer with some authority. Go with "a", or like the previous post, consider a trench drain in front of the garage with a pipe on one end to carry water away. Option "b" will give you a funky "vee" shaped profile in your parking area, as all of the water from the house will have to travel farther to get to "b". As far as the minimum slope for drainage, most paving contractors will say 1% as a minimum, 2% is better. Architects and engineers sometimes design for 1/2%, but that's tough to do with asphalt. One thing to consider - if you plan on being where you are for a length of time, consider 2% slope to the "a" drain. That way in 15 to 20 years you can have a thin overlay of asphalt placed over what you have and not loose your slope for drainage. Go with the minimum drainage and you will be tearing it out and replacing it after that 15 to 20 years, as there will be no room for a thin overlay.
Thanks for the valuable advice! Your pointers and suggestions will make for a winning result.