any suggestions on the proper way to run a downspout underground? our recent torrential downpours here in western nc have begun to cause minor erosion problems in the yard and submerging the runoff for about 10′ in one spot and 20′ in another would be a major improvement.
what sort of piping? what size? how deep? seal it to the downspout or leave an open/covered funnel? ground freezing is only a very minor consideration here.
thanks- don’t want to do it twice!
m
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Replies
We use black corrugated plastic drain tile or the green rigid plastic. Sch 40 if you want to get real fancy.
I'm not green anymore.
what sort of piping?
Usually pvc, but abs is sometimes used.
what size?
4", but that depends on how much water you are running off, too. If you are taking 12,000 sf of roof off in just one d/s, you might need an 8" pipe. I'm guessing that 4" will likely work for the one d/s and for the short runs you are proposing.
how deep?
Now, there's a question. Short answer is actually easy--deep enough to pitch to daylight. You could elbow back up from some depth, but you might be making a mosquito sump out of the d/s leader.
seal it to the downspout
Plumbing supply house will have a d/s-to-pipe connector; you will need to now the size of your d/s beforehand (likely it's 3x4, but it's worth measuring).
The main thing is where it goes. If you are fortunate enough to have someplace above ground to send the water, it's easy. Otherwise you need drywell(s).
Corrugated is cheap, and easy because it comes in long rolls. The advantage to rigid PVC or ABS is that it is rigid, so it will not follow any sags you may have in the floor your trench. Sags can create clogs, though this is less of an issue with a rainwater system (as opposed to foundation drains), since you can generally blast the clogs out with a hose if you have to.
Rigid pipes also (obviously) are smooth on the inside, with make them somewhat less likely to clog with debris.
Edited 7/12/2005 12:23 pm ET by csnow
Keep in mind that clogging is a very likely occurrance, so provision for cleaning must be made.
It's wise to arrange the downspout so that overflow out of the pipe (if clogged or unable to handle the flow rate) will drain "harmlessly", vs depending on the pipe to prevent any such leakage.
4" schedule 35 PVC.
You can use the downspout connectors as cleanouts, but be sure and put in a new one every 360* of fittings and 95' of run from the last access point.
If you have to run under any heavy traffic ways, switch to sched 40 PVC there.
SamT
ARGH!!!!!!!!!!!!!!!I had a long reply complete with links to a nice picture showing how flex tubing and sag and form blockages.But I am not going to redo all of the research."4" schedule 35 PVC."So such stuff. There are Scheduled series of pipes which have constant wall thickness requardelss of the dia. And there are several common Sch available. Sch 40 is the most common for interior water and drain. There is a sch 80 for heavy duty applications. Sch 20 for central vac, and a sch 30, which is use is limited.There are SDR series of pipe, both rigid and flex. It stands for Standard Diameter Ratio and the wall thickness changes with the size of the pipe.But you did not use either of those. As shown in the picture you used S&D (Sewer and Drain Pipe) aka ASTM D-2729. S&D is even thinner wall, but it is the only one with a crush rating (3000 lbs IIRC). But never find out what that is a rating of or how it is measured. S&D and SDR35 have the same OD, at least in the 4" size and can be interchanged. But they have different fittings. But I found that between Lowes, HD, Westlakes, and Feldman's (farm supply) one would have one series of pipes, but fittings for the other series.An adapter is needed to go to from sch 40.SDR 35 and S&D both have an advantage in that they come with bell ends and don't need couplinges between sticks.Both come in two tyes. One with an o-ring ($$) that just fit together and the other plain that you solvent weld.As to sizing 1 4" will carry the full flow from 2 3x2 downspouts. But I check mine during heavy rains and they where only about 60% full so I was comfortable feeding 2 3x2 downspounts plus a short channel drain into each 4".I used about 3ft of corregated on mine to transition from the downspount to the S&D pipe. That saved lots and lots of fitting and elbows. But also allows me to push the tubbing down and away so that I can put a hose in it if need to clear it. Then where they join for the "long run" to the lake I have Y and stubed up a cleanout about 4" below the surface.And I measured and maped everything from the corners and side of the hosue so that I can quickly find it agin.A couple of years ago Andy E had an article on sizing gutters and downspounts complete with forumula and rainfall charts.It is available on the FHB web site.And NDS has some information on the capacity of pipes.http://www.ndspro.com/technical_info/index.aspx
I'd go with PVC as opposed to the black flexible stuff. It's a bit more expensive and harder to work with. But the black stuff can also get crushed more easily. And PVC is easier to eel out.
They make critter guards to put on the outlet end. I highly recommend them as well.
Both of the local big boxes as well as most any lumber yard will have the 4" black corrugated in 10' lengths. They also have a pop-up termination that you can put on the end if you have trouble getting it out to daylight. My SIL's place does not have enough fall around it and I am going to be putting in some of those. Just be sure you have enough fall and slope to keep it from coming back to the house.
She thought she could just bury the pipe and all would be cool. We were there during one of those real downpours and she had a fountain blowing out around each downspout.
View Imagehttp://www.lowes.com/lowes/lkn?action=productDetail&productId=25652-676-422G&lpage=none
Bob
Edited 7/12/2005 2:41 pm ET by RASCONC
i dare any critter to try camping in this pipe. the way it's been coming down lately, a salmon would have a tough go of it.
m
I tried those pop-up elbows like you show pictures of. But with them, the line neveer really gets cleaned out. Sticks, twigs, and gravel off the shingles build up inside the pipe and can't get out.Better to run it straight out to daylight if possible...
Chaos, panic, & disorder - my work here is done.
I agree, I recomended daylight first.