My first post to this group so please forgive me if this has been
asked and answered.
I plan on burying my downspouts and having them merge into one 4"
drain pipe. The discharge will be at a nice point far from my house.
The length will be about 200 ft from the first downspout to the
discharge. There will be a total of 4 downspouts merging into the same
My question is: How many downspouts can I run into a single 4" PVC
pipe within the 200 ft length? I live near Chicago and we get plenty
And ice. I suspect a 4" pipe will freeze up a week after the first
snow and not thaw until April.
IMO- you need to go either with at least a 8" pipe or use shallow
ditches to prevent freezing. The number of downspouts doesn't
matter-- the surface area that you're draining does.
I've got a 12" culvert that takes the water from one side of a 2-car
garage. It has a smooth bottom is well pitched and is on the south
side of the garage-- but it gets 1/2 full of ice sometimes. I'm
glad I didn't use 6" pipe.
gets crossways in the pipe, and jams in a seam at the 100' mark.
If you MUST take your downspouts below ground (and it is seldom a good
idea, IMHO), run them into a collector box, with the outlet pipe halfway
up one side. Make sure the lid is something you can lift off by
yourself, and that you can reach down far enough to clean out the box
once a year or so. Your local concrete flatwork company will have all
the bits you need- this is standard commercial/parking lot stuff.
The traditional method of proper pitch to the finish grade near the
house, and splash blocks, works much better IMHO, and is a lot cheaper
and easier to take care of. At least you are running them away from the
house- idiot previous owner here ran them straight down to the
(basically dead) foundation drains. Guess where the water ended up? I
sawed those off and added elbows before I even closed on the place. My
sister& BIL's place had a buried drain, and the PO either didn't know
how to slope a drain line, or the ground heaved. One failed joint right
below the downspout, and it all ended up in the paneled basement,
starting high on the wall. (It gave my sister, a world-class SWMBO, an
excuse to make him gut and remodel the basement the way she wanted it...)
Good point about the distance. I was concerned about that so I am
planning a having few cleanouts. I also plan to splice in a "tee" into
each downspout before they go under ground. That way if the system
backs up or gets clogged, water that backs up the system will flow out
the tee in the down spout. Plus I'm using pvc and not corrugated pipe
so I can run a snake if needed. Less chance for that twig to get
My yard gets very wet and the drainage is not the best. Any water in
my yard goes to my basement and my sump pump runs about every 3
minutes certain times of the year. I'm also planning a french drain to
divert the underground water which is a bigger problem. So I think
this is the best thing.
Regarding the collector box you mentioned. I like that idea. Can you
point me to a website? I did a search but couldn't find anything. Is
there another term to use? I tried "collector box" and "filter box"
without much luck.
situation. Each downspout runs into its
own flex 4" line, underground to the
edge of the hill. The house is set into
the mountainside. The one place where
the 1 for 1 was not done, was for 2 very
short pieces of gutter, approximately 5'
each, each with its own downspout.
These run to the edge of the hill
through a single 4" line. Also, we
don't really have a frost line here, so
it shouldn't freeze. I used to live in
the Chicago suburbs where everything
froze. I can't tell you how many time
my sump output froze. Unless you can
get it deep and very vertical
underground, it'll probably freeze.
Thanks for the freezing tip. But it will only freeze if water is in
it. If I install it right then after it rains the system will be
empty. Your sump pump output must have had a low spot where water
collected and froze. We have had a very cold winter and mine has been
fine. Even if it does freeze, I'll have "tees" spliced into the
downspouts so the water will back up and flow out the tees.
BTW, I used to live in the Sacramento, CA area. Had no real concept of
the freezing line until moving out here. i think it's something like
3-4' here and my guess is back home it's 4-6".
in my case. I 1 1/2" going underground
and it froze once where it came out at
the property edge. Now the house has
a 4" line going from the house to the
property edge, downhill. The 2 pumps,
120v and 12v, come out from the basement
and go loosely into the 4". The 4" is
large enough that, even in below 0
temps, it will drain. But, I could see
a situation, which snow and ice near the
exit point, where is could dam up and
freeze. But, that's the new owner's
Wanna do this job right the first time-- and pat yourself on the back
every time it rains & your neighbors are pumping their basements?
Then dig deep enough for your cellar to drain to daylight without
those pumps. Size the drain to take your roof runoff & inside and
outside perimeter drains. Solved freezing, and cellar dampness with
You sound like you're fighting the idea of going bigger than 4".
Don't. It is too small volume-wise[unless you have a very small
house], freeing-wise, and clogging-wise.
If you can't afford to do it right, save your time and money until you
I whole-heartedly agree with aem as far as NOT taking the output from
your downspouts below ground.
I'm in east central Iowa -- climate similar to the Chicago area. In
winter, the snow melt and/or freezing rain will not run through the pipe
fast enough to avoid freezing in a shallow 200 ft. line, even a 4" PVC,
especially in a winter like we've had this year. The ice will accumulate
and block the line. I doubt any number of cleanouts will enable you to
clear that line once it's blocked.
If you MUST proceed with your plan to route the downspouts underground,
in winter you could use the cleanouts to dump deicer (calcium chloride
pellets) into the line to PREVENT a freeze-up. This winter -- with heavy
snow and freezing rain and many deep-freeze/melt cycles -- that's what I
did with my sump pump discharge line, a 1.5" PVC feeding into a
dedicated 60 ft. 3" PVC exterior drain line. I have a cleanout (one leg
of a "Y" fitting) where the sump discharge exits the house and enters
the 3" PVC line; the discharge immediately flows through deicer dumped
into the cleanout and carries the pellets down the line. It worked well
but it was a bit of a PITA keeping a good supply of deicer in the line
at all times and that was with only a 60 ft line that served only the
HTH. Good luck.
Iknow you're gonna do it with pipes, but some carefully use
a tiller and a string level, making a gentle and manageable
drainage swale. With plastic from the house, out about 8 feet,
and the dirt used to make a positive slope from the house,
covering the plastic far enough so it gets away from the house.
But anyway, you can convert to 3" pipe after the downspout
transition. Easier to bury. Use good leaf guards up above.
I have two roofs on my 60' long house, one higher than the other. The
one end of the house has level ground, the other has a fairly steep
slope dropping away from the house. The upper roof gutter drains toward
the sloped side of the house, and when it reaches the end of that roof,
it drops via downspout to the lower roof's gutter, then into the lower
roof gutter, then along that lower gutter to the sloped side of the
house. It then drops down a downspout to the ground and into a 4"
plastic elbow connected to a 4" pipe which exits about 30' downhill from
the house. It's been there for 26 years with no problem, except for the
chipmunks occasionally building nests in the pipe, but they are flushed
with the rains.. The same type system is at the opposite side of the
houser, so we're talking about 120' of gutters between the 2. It has
never rained hard enough to overflow the gutters, unless blocked by
leaves or debris, which can happen to any length of gutter that is not
Without doing a lot of math, I doubt whether 4 downspouts draining into
a single 4"' pipe would cause a problem with a standard sized house.
Math would give you the total volume of each downspout x 4, and the
total volume of a 4" pipe, and even if the volume of the 4 downspout is
more than the volume of the pipe, the downspouts rarely, if ever, have
to deal with a full volume of dropping water. If it ever does, somebody
better be building an Ark.
I have checked the flow of water from the 4" round pipe during a hard
rain, and the depth of the water coming out was about 1" to 1-1/2" deep
from each of the two gutters
Thanks. Feeling much better about my decision. I thought about going
up to 6" pipe after the second downspout or even running two separate
lines each taking on two downspouts. But all that is too much work..
and material. I do think that 4 downspouts running into one 4" pvc
line is adequate. Your experience helps me make my decision.
I did that at my house but only had to run about 30 ft to surface it.
At the only entrance to the drain pipe, I transitioned to a 6" collar
and cut a cirlcle of 1/4" hardware cloth to fit inside. After leaves
are down and gutters cleaned, I just lift the circle of hardware cloth
and dump the crud....hmm...I have forgotten to do that for several
years now. Better check it today!
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