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Underground downspout drains - how

WillieWonka's picture

I received a request to route downspouts on a house into an underground drain pipe (which does not exist) and out to the curb. My questions are how is the best way to do this,  using rigid PVC or the black corrugated ADS pipe?

The home sits above the street level about 3 feet as is the ground level. The length of the home front to back is approxamitely 70 feet give or take 10 feet. The downspouts in question here run along this entire length, there about about 4 in all. There is one downspout at the back corner, one at the front corner, and 1 or 2 in between.

the HO wants me to trench from the one farthest back all the way to the front where the curb is and run these 4 downspouts into a main drain that is to drain at the curb. The front of the house is about 10 feet from the curb where the water is to be dumped on the street.

Is rigid PVC better here, say 4" sloped towards the street using Y fittings? And if so is normal PVC cement ok to use below ground?

Or is the black corrugaed flexible ADS pipe used in foundation drains the best route to follow and use Y fittings, couplings and the "sock" over it to prevent sediment from getting inside?

Any opinions on a good professional installation method are greatly appreciated.


If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time.  -ME
If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time.  -ME

(post #98822, reply #1 of 19)

Is there a storm drain or catch basin for you to tie into? Yocan use either sch 40 PVC sewer pipe or flexible ABS (which can be brought without the holes used in footing drains). Order either of them as tightline. We prefer to use the PVC as it lays straighter. The ABS sometimes flexes as the soils compact creating low spots which can fill up with sediment reducing flow rates.

When you bring all of the four inch pipes together I would recommend going to at least a six inch line. If there is a catch basin available you knock a hole through the side, place the pipe and fill it with expanding concrete (Jet Set is a brand name).


Adam Greisz

Owen Roberts Group

10634 East Riverside Drive # 100

Bothell, WA 98011

Wood is Good Adam Greisz<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />  

(post #98822, reply #2 of 19)

Don't forget to check with the town/city as to what is approved.

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(post #98822, reply #3 of 19)

In keeping with what Bob says. These are illegal in many areas. Also a waste of good water. If I have a crew run into one of these (I work as a Roadway designer), we generally remove them as far back as the propertyline, then have the HO remove the rest.

Be sure of where the property line is. If a crew snags it with a backhoe on city land, there is no guarantee that an illegal run will warrant any attention from the city.

At a previous home, I did run my spouts underground to a drywell under a Birch tree. The tree's roots prevented erosion, and Birches like wet soil. This would probably work with any species of tree you see lining riverbeds.

If it can die, I can kill it.
Certified Brown Thumb, 4th degree

(post #98822, reply #4 of 19)

I also used to drywell instead of sending the water down the road. We have a combined storm sewer system in Everett WA. I love the idea of feeding my thirsty vegetation.

Adam Greisz

Owen Roberts Group

10634 East Riverside Drive # 100

Bothell, WA 98011

Wood is Good Adam Greisz<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />  

(post #98822, reply #5 of 19)

My engineer wife and I just put in a similar system in my home, although I don't have quite the slope that you do--more like 1.5 feet.  We used black corrugated 4" pipe (it was cheap) and it works very well.  No problems with the system.  But if you examine fluid dynamics of smooth vs. corrugated pipe, the smooth pipe is, of course, a much better option as the flow will have significantly less resistance.

(post #98822, reply #6 of 19)

I did this a couple of years ago. I used rigid PVC.

The reason being that the corragated flex can collect organic material from the roof which will still there and start "growing" and formin a block. Also it takes a lot more work to keep a constant slope with a sag that will collect water and trash.

But I used about 2-3' section of flex to go from the downspout into the rigid pipe. That saved lots of work getting all of the angles right and it also allows me to easily push it down and away if there is a clog.

Also the rigid is easier to clean out if needed.

And since you are wraping around the house put in a couple of cleanout after a couple of 90's. Put in a Y with a stub up and threaded cap so that it is about 3-6" under the dirt. Then make a map giving the location off the corner of the house.

There are 3 different commonly available 4" pvc pipe.

Sch 40 which is the heaviest and most expensive.

SDR 35

Sewer and Drain (ASTM D-2795 or something like that, not sure of the exact number). It is the lightest weight, and cheapest, but has a crush rating of 3000 lbs.

Use S&D unless you have to go under a driveway or other place that it might get damaged.

S&D and SDR35 have the same OD and will use the same fittings althought technically they are different. You need an adapater to go to Sch 40.

Also S&D and SDR35 come with bell ends so that you just connect one to the other without couplings. But there are 2 types. One with an O-ring and does not need solvent, but is much more expensive. Get the solvent type.

BTW, the mini-excevators are great for this kind of work and you should find them at a rental yard.

. William the Geezer, the sequel to Billy the Kid - Shoe

(post #98822, reply #7 of 19)

PVC is fine, the glue is used underground all the time.  You can also use SDR 35, both are used in this situation. Where I live,[Baltimore,Md. you are required to do your situation].  Just make sure that you have a slope to the curb, it doesn't have to be much; say 1/8 per foot.Lots of luck.

"If all else fails, read the directions"

(post #98822, reply #8 of 19)

As I live in an area with high water prices, I elected to install a large, plastic cistern underground in front of my home. All downspouts lead into it via a 4-6" PVC pipe that has a 1/8" slope towards the front of the home. The footing drains are separate.

The ends of each string of connections around the house has a "Y" cleanout underground as with downspouts it is not a question of if they'll clog, but when.

The cistern will have a small efluent pump that'll water the garden as needed. Excess water goes into a drywell the city made me put in (clay soil, go figure). The drywell overflows into the city sewer, which may, some day, be updated from its current 1880's condition to feature a separate sanitation and storm sewer.

Like others have said, check with the city as to what hoops they want you to jump through before you can get fined. Plus, with the right soil conditions it can be simpler to install a drywell that'll also benefit the nearby plants. I simply went somewhat overboard to ensure that the clay soil that rings my home never gets a chance again to batter the foundation walls to death.

(post #98822, reply #10 of 19)

What is the difference between a drywell and cistern? Why would one be chosen over the other? What are the requirements for each and how are each constructed? Not trying to be dumb, just taking it as an opportunity to learn more about something I don't know much about.

If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time.  -ME

If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time.  -ME

(post #98822, reply #11 of 19)

A cistern is a water-proof tank that is usually filled by rain water. They are quite common in arid parts of the world where every drop of water is hoarded. The modern sub-surface ones usually have three holes in them: 1 inspection port, an inlet, and an outlet. Our cistern is made of some hard, thick thermoplastic and is rated for everything from holding sewage to potable water. When installed properly, the outlet port is lower than the inlet, that way no water pools in the intake. We chose a cistern so as to be able to use some of the water off our roof to water the garden with the help of a small pump.

A drywell is usually a combination of concrete rings with lots of holes and/or loose rock that is set into the ground with some geotextile to disperse water. Naturally, the rate at which water can be dispersed is highly dependent on the local soil conditions. Sand/gravel work best, clay soils stink. Our neighbors needed to dig down 16 feet to find sand so that their driveway would no longer flood. Our dry-well is not constructed that well and will basically hold 500 gallons of water before spilling over into the municpal sewer system. Given enough time, even the 500 gallons will disperse.

Edited 7/20/2005 12:04 am ET by Constantin

(post #98822, reply #9 of 19)

We generally use sced 20 or sched 30 drain pipe that fits together and has Ys available. on this last one, we went with sched 40 because there will be tracks and trucks driving over it. Plan to have 1/4" drop pewr foot if you can. and keep it buried as dep as you can if you are in a frost area. I have seen failures from level pipes that hold water and freeze, from traffic crushing pipes, and from tree roots growing in.
It is also a good idea to screen the exit end or varmints can build nests that block the flow of water



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(post #98822, reply #12 of 19)

We use both PVD and ADS (the black corrugated stuff) as landscape contractors.  We use a Ditch Witch trencher with a 4" chain.  It makes a wider trench = easier pipe laying.  Buy yourself a trenching shovel (ZAK company).

If PVC, use the thin walled stuff.  SCH40 is total overkill, unless like many others have stated, it could encounter compaction.

We use a laser transit to determine the overall grade change from back to front, divide it by the total distance, then trench.  We raise/lower the boom to get close to the desired depth at a given point.  Always go a bit deeper in clay soils, it's easier to backfill a couple of inches (and then jump on it) than to dig it out. 

Do not use perforated pipe of either kind.  It's usually only necessary next to basements.  We've seen roots 20' long inside the pipe.

PVC is superior because it won't suffer near as much from settling.

Like Bill Hartmann said, it's a good idea to run ADS from a downspout into PVC.  The flex allows you to remove the drain from the downspout.

Standard PVC cement is perfect.  The grey stuff is better than the clear.  Remember, this cement is used in irrigation under pressures far higher than your drain will ever see.  If you use ADS, tape your fitting with pipe tape.  It's black with white labeling indicating how thick it is.  It's adhesive makes a decent seal to deter roots.  But in the long run, for you and your fellow man (the next owner), PVC is better.

We usually run 3" pipe from the downspouts, eventually converting to 4" for the final run to the street.  Most places it's illegal to put this water into your sewer (i.e. toilet) line.  We/re in CA, so our rains and yards aren't big enough to require larger pipe.

Consider putting in some collection points/drains in the landscape to collect excess yard water.  Use drain boxes with a small well that sits lower than the pipe outlet.  This collects debris and sediment before they enter the pipe.

(post #98822, reply #13 of 19)

I learned from the code officer today that you cannot dump the water out onto the sidewalk as we planned. Water must be dumped onto the curb of the road, meaning one must go under the sidewalk and cap the sidewalk with a special lid.

That's a joke. The reason is because in the winter time waster will dump onto the sidewalk and freeze. Well duh, if water is collecting on the sidewalk it'l prob collect from regular snow melt and freeze, so what's the point? Geesh, I hate gov't.

If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time.  -ME
If at first you don't succeed, try using a hammer next time...everything needs some extra persuasion from time to time.  -ME

(post #98822, reply #15 of 19)

Pyrotechie, I suppose it depends a bit on where you live. Up here in the Northeast, I have observed some truly impressive iceberg build up from very minor leaks like a trickle from the shut-off valve for the water main for our house.

That valve used to reside in the sidewalk and when it started leaking, the ice floes that followed on the sidewalk were almost impossible to remove. The leakage rate was next to nothing but the supply was pressurized, so the slab of ice just kept growing until the DPW fixed the valve.

From a liability point of view I would also not be caught dead covering a side-walk with water in our climate. All it takes is a thin layer of ice to make people end up on their backsides and possibly the ER.

(post #98822, reply #16 of 19)

I think Constantin and your code official are right - Dumping water on a sidewalk is a REALLY bad idea in a cold climate.

You only live once, but if you do it right, once is enough. [Mae West]

(post #98822, reply #17 of 19)

Draining gutters unto concrete also stains the concrete. 

If there are trees in the vicinity of the house an underground downspout water dispersal system needs to be augmented with some kind of gutter cover system to keep the tree debris our of the gutters and then from clogging the drainage system.  Waterfall is one that I know of.  There are others.  Also, in this situation, black corrugated ABS would not be the best choice of pipe.


(post #98822, reply #19 of 19)

Did the code officer mention what all that water working its way under the sidewalk and heaving in a freeze/thaw cycle would do to your walks?

If it can die, I can kill it.
Certified Brown Thumb, 4th degree

(post #98822, reply #14 of 19)

First, should find out the square inches of downspout. Add the total square inches of all the downspout to gather. That will tell you the size of the pipe running to the street. The square inches of the pipe running to the street, should be at least the total of all your downspout's. Because if the out the pipe has less square inches than the total of all of your feed pipe into it. It will cause water to back up. You're out feed pipe should also be smooth. It should also have one or two clean out installed. So you can use a hose or a snake to clean out any sediment.

(post #98822, reply #18 of 19)


I used 4" PVC with Y's. The gutter installer recommended that as the smooth pipe doesn't give leaves and debris anything to snag on. It would be wise to use gutter screens as a precaution. I would think the corrugated pipe would have low spots and plug easily.