Backed-Up Downspouts

Underground solutions for the overflow

Ask This Old House Crew
Photo by Matt Kalinowski

We purchased an early-1900s barn that was converted to a home about 5 years ago. The place is in great shape but for one thing: Two of the downspouts lead into the ground, and during heavy rains they back up. How can we solve this problem?
— Cathy , Rockport, MA.


Roger Cook replies: First, take down the downspouts and leaders, and remove any debris. If they're clear, the prob-
lem is somewhere underground. I fix this kind of problem all the time.

Downspouts that disappear into the ground send water into a pipe (usually PVC) that leads to one of three locations: to a municipal storm-sewer system, to "daylight" (a point lower than the house where water can flow out at grade level), or to a dry well, sometimes called a catch basin, which is filled with pea stone so water can percolate into the surrounding soil.
But often the drainpipe is stopped up somewhere underground by dirt and leaves, by tree roots, or from being crushed by concrete trucks
driving on the lawn, a common occurrence during remodels. (In daylighted drains, check first for blockage at the discharge end of the pipe.)
Sometimes, dirt and leaves can be poked out with a hand-held plumbing snake or flushed out by sticking a hose with a high-pressure
garden nozzle down the pipe. Avoid power snakes; they'll clear blockages in metal pipes, but can destroy the lightweight plastic pipe that's typically used here.)
If that doesn't work, I fish a metal plumbing snake into the pipe to determine where the blockage is, then use a metal detector to find the end of the snake. (You could also get a pretty good idea where the clog is by marking the snake close to the ground after it hits the clog and then taking it out and measuring from the mark to the snake's end.) Next, I dig up the area around the blockage and cut out and replace the clogged or crushed section of pipe.
If water still backs up after the drainpipe is cleared, then the culprit is probably a clogged dry well. Often, the only solution is to dig it out and replace it. The 50-gallon plastic dry well I use is made with a hatch in the top. That way if the basin ever clogs, it can be cleaned out easily without having to be dug up.
After digging a pit, I lower the assembled well into it, then connect the drainpipe. I like to use Schedule 30 pipe, which doesn't cost as much as Schedule 40 and is harder to crush than lightweight Schedule 20. And before the well is buried, I always wrap it with landscape fabric to keep silt out, then surround it with pea stone to encourage water dispersion.


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