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Drainage

Downspout drainage: how far, how to extend it and when to bury it

By Robert Stulpt Last reviewed

Short answer

Downspout drainage should carry roof water far enough from the house that it keeps moving away instead of soaking in next to the foundation. The Department of Energy’s building guidance says at least 5 feet; I start by thinking about 5 to 10 feet, depending on where the ground takes the water from there. A simple extension is usually the first fix. Bury a line only when you need to, and check local rules before connecting a downspout to any sewer.

On this page
  1. How far should downspout drainage go?
  2. Your options
  3. Buried downspouts: what goes wrong
  4. Can you connect a downspout to the sewer?
  5. Why gutters overflow
  6. How many downspouts, and what gutter size?
  7. Maintenance
Four ways to let a downspout out Four sections of a downspout next to a foundation, with the ground sloping away. Extension: a pipe on the surface carries the water away; it is cheap, visible and easy to check. Splash block: a concrete block spreads a small amount of water on ground that already slopes. Buried line and emitter: the water runs through a buried pipe with a continuous slope to a pop-up emitter at a lower spot. Storm sewer: the buried line connects to the storm sewer, only where a connection is permitted. Schematic, not to scale. Extension Cheap, visible, easy to check Splash block Small amounts of water,ground that already slopes Buried line and emitter Pop-up emitter Continuous slope; outlet lower than the pipe Storm sewer Storm sewer Only with a permitted connection
Schematic, not to scale. Check local rules before connecting to any sewer.

How far should downspout drainage go?

I don’t use one distance for every house. As a field rule, I like to start by thinking about 5 to 10 feet from the foundation, if the ground lets the water keep moving away from there. But five feet onto ground that slopes back toward the house doesn’t help, and neither does ten feet uphill. What matters is where the water ends up: the discharge has to end at a spot where the water keeps moving away.

The Department of Energy’s Building America Solution Center recommends that downspouts discharge at least 5 feet from the foundation. Some localities have their own rules, so check yours.

Your options

A simple extension is my first choice when it works. It’s cheap, you can see it, and it’s easy to tell when it’s blocked. A splash block is for small amounts of water on ground that already slopes well; I don’t count on one to fix a bad slope. I bury a downspout when an extension on the surface would be in the way, or when the water has to travel a long distance, and I want a cleanout or some way into the line whenever possible. A pop-up emitter can work well if the pipe keeps its slope all the way and the emitter sits at a low enough spot, but I don’t want it to be the only way out if it can freeze or get covered. A storm sewer connection is a good solution when there’s a permitted, properly designed connection. I wouldn’t improvise one.

Buried downspouts: what goes wrong

  • corrugated pipe that has been crushed;
  • sediment;
  • roots;
  • a sag (belly) in the pipe;
  • too little slope;
  • joints that have pulled apart;
  • an emitter grown over by grass;
  • a frozen pipe;
  • an outlet that sits higher than much of the pipe.

To check a buried line, I look at the outlet first. Then I run water into the downspout and watches how long it takes to come out and how much comes out. If a lot of water goes in at the top and almost nothing shows up at the bottom, there’s a problem. A camera can help.

Before digging, call 811. Virginia 811 says homeowners must contact it for all digging projects, at least three working days before they dig.

Can you connect a downspout to the sewer?

Don’t assume you can connect to a sanitary sewer, the one that carries wastewater from your house. In Fairfax County, connecting downspouts, sump pumps or French drains to the sanitary sewer without a permit is illegal, because the extra water can overload the system and cause sewage overflows (Fairfax County). The City of Alexandria also says that connecting sump pumps and roof downspouts to the sanitary sewer is not allowed (City of Alexandria).

A storm sewer is different. Alexandria, for example, requires roof drains and sump pumps to be connected to the city’s storm sewer where an inlet is available, which for one- and two-family homes means within 100 feet of the property line. Since a 2013 ordinance, the city can allow alternatives, including letting roof drains discharge to the street gutter at the director’s discretion (City of Alexandria, Memorandum to Industry 05-14, 2014).

So there’s no single rule for Virginia, let alone the whole country. Check the local stormwater and sewer requirements before connecting a downspout to any public system.

Why gutters overflow

In my experience, roughly from most to least common:

  1. Leaves and debris.
  2. A blocked downspout.
  3. An outlet that’s too small or blocked.
  4. A gutter with the wrong slope.
  5. Too much roof area for a single downspout.
  6. A gutter that’s too small for that roof and that rainfall.
  7. A roof shape that concentrates too much water in one spot.

I’ve also seen a gutter that was sized perfectly well look too small because a roof valley was dumping half the roof into three feet of gutter.

How many downspouts, and what gutter size?

I don’t use a rule of my own, like one downspout every so many feet. Sizing depends on the roof area, the roof pitch, how hard it rains where you live, the size of the gutter and the downspouts, the valleys, and how many outlets there are and where. For a new system, I’d rather the gutter installer work it out from rainfall data and roof area. I diagnose drainage; I don’t try to be a gutter designer.

Maintenance

  • Keep the gutters clean; debris is the most common reason they overflow.
  • Check that the downspout outlets aren’t blocked.
  • On buried lines, run water in at the top now and then and see how much comes out at the bottom.

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