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Installing Downspout Drain Lines

DEAR TIM: I need to bury downspout drainage pipes in my yard before the yard is seeded. Where is the best place to put them and how deep should they be buried? What type of pipe do you like? How far away from the house should the pipes extend? A friend suggested using pop-up valves to help water the lawn and plants. Are those a good idea? Rich T., Jackson, MS

DEAR RICH: Stormwater drainage from roofs is a topic sometimes ignored by builders and homeowners alike. I can't tell you how many houses I see where the downspouts empty onto a splash block at the base of the foundation. Often these homeowners are plagued with water seepage into basements or crawlspaces and it's no wonder. A heavy rainfall on an average sized roof can produce hundreds and thousands of gallons of water that spew from the different downspouts located around the house.

There is a hard 90 degree fitting in the ground in the lower left corner of this photo. All of the other fitting angles are clearly at 45 degrees.

There is a hard 90 degree fitting in the ground in the lower left corner of this photo. All of the other fitting angles are clearly at 45 degrees.

I regularly visit the Southwestern part of our great nation and am somewhat astonished that stormwater is not collected and stored by homeowners that live in this arid area that is in the clutches of a punishing drought. Rainwater can be easily collected and piped to above or below ground plastic barrels or tanks. If the storage is above-ground and placed at the highest part of the lot, drip irrigation piping can be extended from the water storage. The stored rainwater can then be used to help irrigate plants that otherwise would have enjoyed the drink before the house was built.

Before you proceed with any work, you should check with your local government to see if they have special stormwater rules and regulations. Sometimes you have to pipe this water to special underground storm sewers or above ground channels. Some local governments or agencies have no rules or regulations.

I usually dig a trench about 12 to 14 inches deep for downspout drain lines. If the lot is fairly flat, the pipes will get deeper the farther they extend as you should create 1/8 inch of fall for every foot the pipes run. The pipes should never be buried in the non-compacted fill dirt that is placed against the foundation. Over time this dirt or soil settles and it can cause piping to break, kink or develop reverse, or backwards, slope. Downspout piping can cross the uncompacted fill at a 90 degree angle so that it is placed in undisturbed soil. But as the soil adjacent to the house settles over time, this small length of piping needs to be checked and lifted to ensure it drains.

Smooth 4 inch diameter plastic SDR-35 sewer pipe is the material I prefer to use. This pipe has a smooth interior and closely resembles the thick-walled plastic piping used for interior house drain and vent piping. Fittings can be permanently welded to the pipe with PVC cement or you can buy rubber gasketed fittings that require no glue. If you install either type as directed, tree roots that create clog nightmares will never be able to enter the piping system. I am not a huge fan of the corrugated flexible black piping for downspouts. It can crush easily and it is nearly impossible to clean with professional drain cleaning equipment.

If this was a job in an existing lawn, I would have used plywood next to the trench as I operated the ditching machine. But since this is new construction and the yard needs to be final graded, it didn't make a difference.

If this was a job in an existing lawn, I would have used plywood next to the trench as I operated the ditching machine. But since this is new construction and the yard needs to be final graded, it didn't make a difference.

All underground bends in downspout piping should be made with 45 degree or smaller angle fittings. 90 degree angles underground become obstacles in the event the piping has to be cleared by a professional drain-cleaning company. You can use a 90 degree angle at the base of the downspout where the underground piping begins, as a drain cleaner can usually insert his metal snake here with no difficulty.

If you are allowed to drain your stormwater on your own lot, do so as far away from your home as possible. Try to pipe all water to a low point away from your home. Do not drain more water to a point on your lot than would have ended up there naturally before your home was built. Simply keep in mind where the water is falling on the roof and where that water would drain if your house had never been built. If you pipe the water where it used to go, you should not harm any of your surrounding neighbors.

Inline popup valves do a good job of allowing rainwater to discharge onto your property, so long as you are allowed to drain the stormwater on your property. Try to strategically place them where they will do the most good for your vegetation.

An invaluable tool that will come in handy in future years is a collection of photos that are shot as the downspout piping is being installed. If you stand back and include parts of the house in the photos and place shovels or other objects in the photos for scale, these prints will help you locate the pipes in the future. Over time it is very easy to forget where hidden pipes pass in the ground.

My own photos saved me a ton of work just last year. I had to install a small field drain in a side yard. The photos I had taken 17 years before allowed me to locate within five minutes the drain pipe to which the new drain was to be connected. I could have dug for an hour and missed the pipe by inches without the aid of the photographs.

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7 Responses to Installing Downspout Drain Lines

  1. Hi Tim,

    Re: "I usually dig a trench about 12 to 14 inches deep for downspout drain lines." -- would the same depth be sufficient in Canada where I live? I was talking to somebody at Home Depot and they repeatedly warned me that no underground drainage pipe should be closer to the surface than 4 feet (for the fear of freezing).

    Would appreciate your opinion -- I am about to start a drain pipe burial project, don't want to dig too much, but if freezing is a concern, I'd probably have to go deeper than 4 feet.

    AG.

    • Alex, your question requires lots of typing, plus I have some questions for you so I can give you the correct answer(s). I only do pithy answers here in the comment section. If you want to protect the investment you have in your house and not waste time or money *hoping* you make the right decision, you should talk to me on the phone for just 15 minutes. It'll be the best investment you've ever made in your home!

      • Hi Tim
        We have a crew who is currently installing the under ground spouts, I noticed they have only dug down maybe 8" we also live in Canada and it can really get cold! I would like to know the proper way to install before our guys leave....thanks

  2. Tim,
    Same question on the underground horizontal drain lines for down spouts. My experience has been the horizontal lines freeze (glacier style) and eventually block the pipe closest to the exit point. ALL lines eventually exit at ground level away from the house and therefore the ground freezes HARD in that vicinity...thus the glacier ice. HOW do you prevent this? Add a heat tape? And IF yes, one has to remember to turn it on/off as the conditions change. Oftentimes it is very cold with NO snow melt off the roof, so heating the pipe is not necessary. Will the heat tape damage the plastic pipe? What IF Schedule 40 was used? Thanks in advance for your advice. We are doing a NEW home build and want this to be taken care of permanently. Plus, some of the drain lines will go "under" paved areas like a driveway and/or patio. Therefore, got to get this right.

    • Install a wye fitting and above-ground clean out far upstream where you can open it and add a very salty brine hot-water solution IF it does freeze.

      Brine should melt the ice and open the line.

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