Roof Downspouts & Leaders: Defects, Leaks, Repair Guide
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Downspout or gutter leader 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
Roof gutters downspouts & roof drainage control systems
Questions & answers about roof drainage systems: downspouts & leaders: installation, maintenance, repairs, leaks, screens, routing, clogs, and just about anything else.

Gutter roof drains, downspouts & leaders: Here we decribe the types of defects or leaks in the downspouts or leaders for roof drainage systems: leaks or other defects that cause basement or crawl space water entry.

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Roof Downspout or Leader Defects

This article series discusses how to choose, install, diagnose & maintain roof gutters & downspouts, & roof drainage systems to prevent building leaks and water entry. Our page top sketch is provided courtesy of Carson Dunlop Associates.

See GUTTERS & DOWNSPOUTS for a guide to types of roof gutter systems. See GUTTER DEFECTS LIST and DOWNSPOUT / LEADER DEFECTS for examples of common mistakes in handling roof runoff. Also see EAVES TROUGH, INTEGRAL GUTTERS and YANKEE GUTTERS that are discussed in separate articles.

Quoting from Carson Dunlop Associates' Home Reference Book:

Downspouts collect water from the gutters and discharge it into drains or onto the ground. Underground drains (usually made of clay tile, cast iron or plastic) become clogged or break below grade. If an underground downspout malfunctions, water problems will likely develop in that part of the basement. There are two options.

Exterior digging and repairs can be undertaken; however, it is faster and cheaper to simply disconnect the downspout and redirect it to discharge away from the house. It’s also easier to monitor the performance, and problems are corrected easily. Downspouts should discharge above grade onto the ground at least six feet from the home. The slope of the ground in this area should be away from the house, to direct water away from the basement.

Our list of common downspout or leader defects shown just below is followed by illustrations or photographs of many of these conditions. Gutter defects are discussed in detail separately atGUTTER DEFECTS LIST

Downspout empties too close to the building, concentrating water against the foundation, a very likely source of basement or crawl space water entry. Details are at Downspout Extension Spills Too Close
Downspout empties onto soil that slopes back towards the building. Details about controlling surface runoff and roof drainage disposal by proper site grading are found at Surface Contouring to Dispose of Surface or Roof Drainage Runoff
Downspout connections facing wrong way - leaks. Details are at DOWNSPOUT LEAKS
Downspout buried sections using perforated pipe near the building. Details are PERFORATED PIPE DOWNSPOUT DRAINS
Downspouts connected to footing drains, building interior drains, floor drains, or sewer system (storm drain connections are ok). This is a common but serious mistake made by uninformed builders. Adding the load of roof runoff to building foundation drains overloads that drain system and invites basement or crawl space water entry and even flooding. A basement flood from this mistake can happen very suddenly, often less than 10 years after new construction, when a hand full of leaves or other debris enters and clogs the footing drain system through the gutter and downspout system. Details are at DOWNSPOUTS BURIED / BELOW GRADE
Downspouts clogged at gutter connection, elbows, or anywhere in their routing. See DOWNSPOUT DEFECTS, MORE
Downspouts damaged by clogging, ice, frost, animals: splits, holes, tears, leaks. See DOWNSPOUT LEAKS
Downspouts disconnected, loose, or missing. See DOWNSPOUT LEAKS and DOWNSPOUT DEFECTS, MORE.
Downspouts (& gutters) missing from upper or secondary roofs. See DOWNSPOUT DEFECTS, MORE
Insufficient size or number of downspouts to handle roof drainage water volume. In general, provide a downspout for every 35-40' of gutter length. More downspouts may be needed around complex roof structures. See DOWNSPOUT DEFECTS, MORE
Buried downspout lines made of perforated pipe close to building. Details are at PERFORATED PIPE DOWNSPOUT DRAINS

Downspout Extension Spills Too Close to the Building

Gutter and Downspout Details (C) Carson Dunlop Assoc

The sketch at left illustrates a major cause of wet basements and crawl spaces: the downspout ends too close to the building, backfill at the building has settled, and in addition, the original grade left from the excavation to build the foundation remains as hard-packed soil that directs spillage back towards the structure.

Sketch courtesy of Carson Dunlop Associates.

Our photos below illustrate downspouts emptying too close to the building. At below left you can see erosion that is sending most of the roof runoff out of the downspout and right down the foundation wall. At below right a downspout is terminated on the deck surface. That detail can lead to slip/fall hazards (slippery algae-covered deck boards) and basement water entry (due to in-slope grade towards the building, hidden below the deck surface.)

Downspout empties too close to building (C) Daniel Friedman

Downspout spills on deck (C) Daniel Friedman

Downspout Empties onto Settled Backfill

Here we show the most common roof drainage system error that leads to basement or crawl space water entry: the downspout empties too close to the building foundation wall.

This mistake, combined with settled backfill that slopes back towards the building sends this concentration of water from the roof right into the building.

While there are rules of thumb for the length of downspout extensions (minimum of six feet, or more from the building), the common sense downspout rule is:

When the water leaves the end of the downspout, it should keep going away from the building, not back towards it.

Sketch courtesy of Carson Dunlop Associates.

Downspout Empties onto Sloped backfill over compacted in-slope virgin soils or clay

A more subtle version of the "downspout too close to the building" problem we described above is illustrated in the sketch at left.

After a building foundation and structure have been completed, backfill may have been spread around the building and may appear to slope nicely away from the structure.

But because the new backfill is less compacted than virgin soil, even though it slopes away from the building, water soaking through the backfill may encounter below-ground hard-packed original soils that slope towards the structure.

The result is a hidden in-slope grade problem sending roof spillage or downspout spillage right back into the building.

Sketch courtesy of Carson Dunlop Associates.

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GUTTERS & DOWNSPOUTS - see detailed links at page left

Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. Thanks to Alan Carson and Bob Dunlop, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education including the ASHI-adopted Home Inspection Training Program (home study course), publications such as the Home Reference Book, report writing materials including the Horizon report writer, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
Building Pathology, Deterioration, Diagnostics, and Intervention, Samuel Y. Harris, P.E., AIA, Esq., ISBN 0-471-33172-4, John Wiley & Sons, 2001 [General building science-DF - ** Particularly useful text **
Dampness in buildings, Diagnosis, Treatment, Instruments, T.A. Oxley & E.G. Gobert, ISBN 0-408-01463-6, Butterworths, 1983-1987 [General building science-DF]

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.

Carson Dunlop's Home Study Course for Home Inspectors can be examined online at that company's website. More about home inspector education and other educational materials is organized at InspectAPedia.com at Home Inspector Education.
Certainteed Weatherboard fiber cement siding and trim products - see certainteed.com/ or see certainteed.com/resources/sidingandtrimspecsheet.pdf
"Flashing: the plain solution to leaky walls", Thomas E. Remmele, Manager, Technical Services, Sto Corporation, Building Standards, November/December 1999 p. 21-25.
"Weather-Resistive Barriers [copy on file as /interiors/Weather_Resistant_Barriers_DOE.pdf ] - ", how to select and install housewrap and other types of weather resistive barriers, U.S. DOE
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Roof Downspout or Leader Defects

Downspout Extension Spills Too Close to the Building

Downspout Empties onto Settled Backfill

Downspout Empties onto Sloped backfill over compacted in-slope virgin soils or clay

Questions & Answers regarding this article

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Technical Reviewers & References

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair