Q&A / 

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.


21 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.


    • 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.

  3. Tim,

    You recomend 4" diameter pipe, but I am trying to determine how many downspouts I can run in one 4" diameter pipe. I live in KY and the way the lot is set up, I will have plenty of slope and it will be draining into a creek, but the square footage of my roof is approx. 4500 sq ft. This is a new construction and I am trying to get the drains installed before I sow my lawn this fall. I have had people recomend running a 4" line for each drain and others saying that all of them could drain in one pipe. Thanks for any help that you can provide.

    • Put half the roof on a 4-inch pipe and the other half on another 4-inch pipe. Where the two pipes meet to run to daylight, increase the pipe size to 6 inches.

  4. Tim,

    I need to run the roof runoff from the gutters to a lake behind my house. I currently have the gutters draining into 4" PVC and then into 2 lines that are 6" PVC. The roof is 5000SF. The PVC is buried. during heavy rains one of the runs to the lake doesn't seem to keep up. The rain overwhelms it. The landscaper says that it's because the run drains into the lake below the waterline. Does this sound right to you?

    • Yes. If the outlet of the pipe is UNDERWATER, then the water pressure in the lake is reducing what can run through the pipe. The outlets of the drain pipes MUST be open to the air for maximum flow.

  5. Hi Tim,

    Will pop-up emitters freeze up in the Midwest (northwest Missouri)? If so, what is a good alternative solution? Thanks in advance.

  6. I live near Detroit Mi, we have lots of snow and frost. We've been installing underground downspouts in our area for over 20-years. Our area is mostly clay so we need to take the water away from the home, to keep the basement dry. I sell a system with a filter installed under the downspout (just before the system inters the ground), then go at least 10-ft away from the home to a 4" pvc tee, a strainer on top to discharge water installed over a post hole filled with pea gravel. The tee over the gravel (what we call a mini French drain) prevents the system from holding water for very long.


    I'm a college-trained geologist with a specialty in hydrogeology - the study of ground water. I'm sad to tell you your system has virtually no ability to dissipate water because the deeper you go in clay soils - into the B horizon - there's LESS ability for the water to move through the clay. What's more, most of the post hole is filled with stone so there's very little capacity to hold water. I'm afraid your system is based on bad science.

  7. Jonathan Lozier
    Great website and very informative. I plan on installing a french drain with 4" perforated HDPE approximately 30' in front of my house. I own a backhoe which is necessary in order to dig through my very heavy clay soil. I have plenty of room for pitch and the overall length is rough 150' around the back of the house. I plan on burying the gutter downspouts with 4" solid HDPE and having it run right over top over the perforated out to day light, essentially stacked.I figure dig one hole for several purposes, the roof water is not going into the french drain pipe it will be contained within its own solid pipe. One 4" solid pipe for each down spout. Question: I live in upstate NY and the winters are rough, I am very worried about the 'glacial effect' within the drain pipes, how do prevent that? do I have to dig down 4'?
    Thanks for your time

  8. Tim,
    First let me say " Thank you " for the time & effort you freely invest into this site.
    I recently ripped up all the grass (weeds) in the backyard of our new house. We live in Pennsylvania area incase that may effect your opinions. Currently our rain spouts empty where they end and I know this is the worst possible case. While the backyard is nothing but dirt Id like to install a drainage system to remove water away from the home. Backyard is approx 60ft from back of home to rear fence, slightly sloping away from house. Outside of rear fence is a 20ft evesmeant between the neighboring yard. My plan is to install a drain box w/grate under each downspout, each traveling to one of Two main 4in PVC (one main for each side of house) each main will end discharging into one of two buried perculating dry wells.
    My soil makeup is mostly Clay, I did a Perc Test by digging 4ft deep hole with a post hole digger & filling with water, after three days the water has dropped maybe 2inches. so my concern is will the drywell perc system even work for me? If not what might you suggest?? I'm also planning on putting a 12x12 shed in the lowest back corner of the yard on a concrete slab, have the area dug out to begin preparing the base for the shed. It recently rained and I noticed the hole filled with water in the one corner which sat pooled for some time.. I need to do whatever I can to address drainage prior to pouring cement for shed slab and seeding the lawn. I know this is a lot to take in but I figured the more information i give the better you might envision my situation. Thanks in advance for any help your able to offer.

  9. The fact that people in the southwest (of the United States) don't collect rainwater is not surprising because it's actually illegal. "Water rights" is the "third rail" in politics in the west. If water falls on your ground and you don't have rights to it, you have to let it go downstream.

  10. We bought a house ten years ago previously owned by wanna-be gardeners who installed a lot of "stuff" we are just now discovering. One of those things is a downspout that goes into the ground. We have no idea where the water is draining; that side of the house is very close to our neighbor's property. Would the City be able to tell us if that pipe flows into the City sewer system? This house was the first built in the neighborhood...Are there any other clues we could look for? The house sits on a slight hill so the logical thing would be a pipe that comes out somewhere near the street/curb near that side of the house, but not seeing anything like that...

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