Downspout Drainage questions - HELP!

Discussion in 'Homeowner Assistance Forum' started by pbmendez, May 21, 2006.

  1. pbmendez

    pbmendez LawnSite Member
    from Houston
    Posts: 2

    We are having a new driveway poured. As preparation for this, and to help pull water from the foudnation, we want to connect the 4 or 6 if possible downspouts to an existing drain line that runs the length of our lot (approx 90')

    To set the image: The existing 4" thin wall drain line is on the far end of the driveway - going parallel to the drive. The house and downspouts are across the drive (approx 13')

    We are in Houston, TX - so not a ton of rain here - assuming we don't get any hurricanes.

    Questions:

    can we connect 4-6 downspouts to a 4" drain line.

    We have dug a trenc - getting the slope is what is proving challenging. Do you suggest starting at the highest point in the run or the lowest and working bckward?

    Beside the 4" pipe we are running 2 - 3/4" electrical condiuits the length of the drive. We have our trench approximately 6" wide.

    Once the pipe is in there, is it sufficient to fill the trench just with the dirt we removed, taking care to compact it? Or do we need rock? Should we be putting the pipe on a bed of rock/gravel etc.?

    We are planning for the top of the pipe to be a minimum of 9" from the top of the anticipated concrete. Is that sufficient to avoid cracking of the driveway?

    Lots of questions, thanks for answering whatever ones you can. We have spent a couple days out there, adjusting thingns alot. Your help is appreciated.
    :dancing: :dancing:
     
  2. Dirty Water

    Dirty Water LawnSite Fanatic
    Posts: 6,794

    4" drainline can move more than 100 gpm. More than adequate for even the worst of storms.

    Have it pitched properly is important, once the trench is dug and the pipe is laid, go over the entire run with a level every few feet and make sure you have good fall, you only need 1" or so every 10 feet.

    Is this drainline going somewhere (Curb, drywell?) or is it a perforated line that will seep out all the water during the run?

    If your are just moving water, you don't need to lay down rock with the pipe, if its designed to be a french drain then line the trench with a fabric barrier, put down a few inches of 1 1/4" drainrock and then lay your pipe, backfill with a few more inches of drainrock and wrap the fabric around that. The purpose of the fabric is to keep the soil and drainrock from mixing and ruining the draining purposes.

    After that, you can backfil with soil.

    9" is plenty deep to not crack the concrete, however you will need to have very good compaction or it will develop hairline cracks as the ground settles.
     
  3. tylermckee

    tylermckee LawnSite Member
    from wa
    Posts: 248

    4" pipe will handle damn near any residential house downspout drains no problem. I would just start from the top and work your way to your existing drain, give yourself as much slope possible, shoot for at least 2%, less will work but the more the better. once you get the pipe laid run along the length and make sure you dont have any "bellies" in it (where it dips, bows, etc). backfill with dirt is just fine, just keep the big rocks off the pipe. 9" is plenty of cover just run some type of compactor over it a few times. Such a shallow trench you dont really need to backfill and compact in lifts.
     
  4. pbmendez

    pbmendez LawnSite Member
    from Houston
    Posts: 2

    Is this drainline going somewhere (Curb, drywell?) or is it a perforated line that will seep out all the water during the run?

    The drain at the end of the run, crosses the drive and connects to the existing drain line which exits at the curb into the street.

    9" is plenty deep to not crack the concrete, however you will need to have very good compaction or it will develop hairline cracks as the ground settles.

    Great, Thanks!
     
  5. gammon landscaping

    gammon landscaping LawnSite Senior Member
    Posts: 550

    more fall the better is incorrect! you can move more water through a level pipe than a pipe on a 45 as any plumer will tell you. it has more to do with friction in the pipe than water speed. but some slope is fine. there is no way for us to know if a 4 inch pipe will handle you flow untill we know the size of your house. i 1200-1800 sqft worth of roof. you should be fine if your house is 2000-3000 sqft you would probably want to run a 6 inch line. but another pluming fact, 2 4 inche pipes will not carry the water of 1 6 inch pipe. a 6 inch pipe will carrie about 2.25 times the water of 4 pipe. it works out cheaper. another thing to consider is the drain pipe you are running it into. what is it? if it is a roof drain, what will be the volume of water in it. if it is a basement drain or footer drain then you could have a problem if it ever becomes cloged, it could flood you basement. just some thoughts if it is a small home and it is another roof drain you should be fine
     

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