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I have two downspouts whose discharge I need to get past a sidewalk. Currently for each gutter, corrugated tubing is run underground, under the sidewalk, for approximately 20 feet where it discharges out the side of the hill approximately 18 inches lower than where it began (it's not a steep hill).

One of the corrugated tubes has a dip in the middle of the run which isn't ideal, but otherwise during the summer this configuration works decently for the time being. In the winter is a different story--the tubing quickly freezes up and remains frozen until the ground thaws, which creates big problems for roof melt-water and early-Spring rainfall.

In the winter I've tried disconnecting the tubing and installing downspout extensions that run to the near edge of the sidewalk (so the water runs across the top of the sidewalk and then down the hill). This allows the gutters to drain properly but creates some icing problems on the sidewalk. I don't leave it like this in the summer due to concerns that the quantity of water will erode the concrete in those areas.

What is the ideal configuration so it can drain properly?

I've attached a crude sketch and a photograph.

Sketch: sketch

Photo: photo

  • does the one that doesn't have a dip in it drain properly in the winter? – DrewJordan May 26 '15 at 16:58
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    Anything preventing digging the defective one up and giving it a proper gradient so it will drain? Or does it do a tremendous dip under the walkway? – Fiasco Labs May 26 '15 at 18:23
  • Neither of them drain properly in the winter. The discharge end covers with snow and then eventually it'll freeze back up the whole tube. – Luke Z May 27 '15 at 0:15
  • I have the same problem. I am considering simply switching the configuration twice yearly and running the downspouts into pipes that rest on top of the sidewalk during the winter season, then converting back to underground pipes the rest of the year. Have not figured out the best way to do that and I wanted to avoid that but I don't want stuff freezing and backing up either. – user44684 Oct 18 '15 at 13:42
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The preferred solution that I've seen is to discharge the gutter through a couple inch air gap into a catch basin that outputs into the underground drain. The air gap allows for water to drain into the yard when the catch basin freezes solid.

And while it's a bit late to change your underground drains, I prefer the solid pipe installed with a slight slope over the corrugated tubing. It's less likely to collapse over time and water doesn't have anywhere to be trapped in the tube.

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One option to consider is adding a heating wire to each pipe, perhaps extending into the bottom of the downspout. That way water can flow away and not over the sidewalk. The heater does not need to operate 24x7. A thermo control could engage it at a suitable range of pipe temperatures (or representative air temperatures). Perhaps from 20–31 °F (-7 to -0.5 °C). Warmer than that and water will flow freely. Colder than the low end and probably no water would be coming from the roof.

Another idea is that it looks like the eave might be wide enough to put the gutter mostly past the sidewalk. Instead of discharging into the downspout, what if it were disconnected and replaced with a rain chain? It can slant outward somewhat to keep the sidewalk drier.

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