Buried Downspouts & Underground Drains for Roof Runoff
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• Buried or underground roof drainage downspout defects, clogging, overflowing, holes corrosion, leaks that cause wet basements or crawl areas
• Proper installation of buried downspout extensions
• Proper installation of French drains & seepage pits at flat sites
• Gutter & downspout defects cause wet basements & crawl areas
• Questions & answers about installing, maintaining & repairing buried roof drainage piping, downspouts, leaders

Photo of a Buried Drain Line that Should be Abandoned

The buried downspout drain line shown at left is one that we'd recommend abandoning - it connects to a drain line that enters the building through the foundation wall and passes below the basement floor, incorporating a basement floor drain, ultimately connecting the the sewer line.

Buried or below-grade downspout extensions in new construction are (or should be) directed either to "daylight" downhill from the structure so that water will drain away from the building by gravity, or they are connected to a storm drain.

For flat sites it may be necessary to drain into a drywell or "French drain" system or into a pumping chamber that sends drainage to a remote storm drain or drywell. See FRENCH DRAINS for details of handling roof runoff at flat or poorly-drained sites.

When a buried downspout line has become blocked (or if you're not sure if it has become blocked) we recommend that you disconnect the downspout above grade and install an above-ground extension to direct water away from the building. This step can stop basement flooding from several hidden downspout drain problems including

• Clogged or broken buried downspout drain line
• Buried downspout line (stupidly) connected to the building footing drains
• Buried downspout line connected to drains that run through and/or under the building basement floor
• Buried downspout line connected to local septic or sewer piping

Sketch courtesy of Carson Dunlop Associates.

The dramatic roof drainage leak shown at left includes several interesting observations made at this nearly-new home:

• The roof gutters were overflowing, sending water down and behind vinyl siding - you can see water pouring out of the "J" channel at the center of our picture of this Pawling New York Home.
• The buried downspout line (visible under the deck) was blocked
• The ground under the deck was lower than surrounding soils (the deck was constructed before final backfill and grading were performed), forming a "pool" of water against the building rear foundation wall.

These conditions are likely to lead to basement flooding, if not immediately, as soon as the footing drains clog or a crack opens in the poured concrete foundation wall.

The sketch at left illustrates several reasons why it's a bad practice to connect roof drainage downspouts to drains that run through the building or under the building floors.

• Clogs in the vertical section of the downspout can lead to leaks through the building foundation wall.
• Blockages in the under-floor drain combined with high volumes of roof runoff water entering the system send the entire roof runoff into the building basement or crawl space
• Debris flowing down the downspout drain (leaves from gutters) can block floor drains or even the main building sewer line, leading to sewage backups into the structure.
• Debris flowing down a downspout drain that has been (foolishly) connected to the building foundation drain system can block that drain leading to basement flooding from either roof runoff or surface and subsurface runoff, or both.

Sketch courtesy of Carson Dunlop Associates.

Some builders consider that if they use perforated 4" drain pipes to transport roof drainage away from the building, the water will "soakaway" harmlessly into the soil even if the end of the buried drain line is blocked or never taken to daylight. Both of those are mistakes.

• Perforated buried drain lines near the building allow roof spillage to leak against and into the foundation wall.
• If the downspout line end is not taken to daylight where water can continue draining away from the building (or to a storm sewer), the blocked line will eventually back up in times of heavy rainfall or wet soils, leading to building leaks and water entry.

If we see perforated drain lines close to the building (photo at left) we expect that the building will eventually have a basement water entry problem. A "fix" for this problem is to abandon the buried drain line entirely. See Buried or "Below Grade" Downspouts for more notes on abandoning buried drain lines.

As our photo illustrates (left) it is usually a mistake to connect a downspout line to a buried pipe that is too small - in this case obviously smaller than the downspout drain itself.

In periods of heavy rain the small-diameter plastic pipe shown here won't handle the volume of water running off of the roof.

On occasion we find that a buried downspout line has been used to dispose of basement or crawl space sump pump water. That's probably fine. But don't use your buried downspout line to dispose of graywater from sinks, laundry systems, or showers. In most communities it is illegal to dispose of gray water on to the soil surface or into nearby waterways.

Our photo (left) shows a basement sump pump drain line connected to a buried downspout drain.

And be sure that the buried downspout drain line that you are using to carry off sump pump water is properly installed and that it is not connected to the building footing drains.

Watch out: We have found buildings whose sump pumps were busily pumping away trying to get rid of basement water while discharging the water to an improperly installed drain that simply sent the water right back into the footing drain and right back into the basement.

• The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop, and from the InspectAPedia bookstore. The 2010 edition of the Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ^® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.