I am running my downspouts to buried pipe to be piped away from my house. The side I am working on has two downspouts. I am also adding about 5 small atrium drains. The underground pipe that will lead to daylight will be about 70 feet long. (This is not a straight run, there are curves as I am going parallel to the front of my house, turning, then going parallel to the side of my house.)

In that 70 feet, there will be approximately 17 inches of drop.

What size/how many underground pipes would you recommend?

On 10/21/2015 9:15 AM, wrote:
I am running my downspouts to buried pipe to be piped (snip)

What size/how many underground pipes would you recommend?

It all depends oh how much water you need to get rid of and how many
leaves dead gophers and snakes have accumulated in the pipe. For a
straight run here ya go, it's a start ..
http://www.calctool.org/CALC/eng/civil/hazen-williams_g

On 10/21/2015 9:15 AM, wrote:
I am running my downspouts to buried pipe to be piped away from my
house. The side I am working on has two downspouts. I am also
adding about 5 small atrium drains. The underground pipe that will
lead to daylight will be about 70 feet long. (This is not a
straight run, there are curves as I am going parallel to the front
of my house, turning, then going parallel to the side of my
house.)

In that 70 feet, there will be approximately 17 inches of drop.

What size/how many underground pipes would you recommend?


Do you live in a climate where temps go and remain below periods for
longish (more than two weeks) periods? If so, you'll need a wider
diameter pipe to handle the occasional ice buildup inside the drain
pipe. Same for if your area gets substantially heavy rains at times.
If you've got significant roof area, you'll have a lot of run off, and
that has to be factored in also.

I live in a small house in Minnesota and ran two french drains from my
downspouts. The longest starts in the back, runs along the side and
connects to the downspouts at both corners, then runs downhill until
the end peeps out of the ground - about a fifty foot run in total. I
used a four-inch diameter pipe, but it couldn't handle all the runoff
from both downspouts during the very heaviest rains, so I ended up
running a new drain from the front downspout. I have a third french
drain from the downspout on the opposite corner, again with a
four-inch drainpipe, about an eighteen foot run, and it's worked out
fine.