Bad downspout connection (C) Daniel Friedman Where do Leaks Occur at Roof Downspouts or Leaders?

  • DOWNSPOUT LEAKS- CONTENTS: Common Leak Points on Downspouts & Downspout Connections - Downspout defects, clogging, overflowing, holes corrosion, leaks that cause wet basements or crawl areas
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Roof drainage downspout leak points:

This article describes the places where you are most likely to find leaks in the building roof drainage system downspouts or leaders.

This article series discusses how to choose, install, diagnose & maintain roof gutters & downspouts, & roof drainage systems to prevent building leaks and water entry.

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Common Leak Points on Downspouts & Downspout Connections

Gutter and Downspout Details (C) Carson Dunlop Associates

Article Contents

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Common leak points at downspouts include:

  • Upper elbow below the gutter, leaking at seams and elbows due to damage from clogging and frost
  • Downspout leaks at vertical seams that have burst from swelling wet leaves or frost
  • Clogged lower elbows near the lower end of the downspout

Sketch courtesy of Carson Dunlop Associates.

Downspouts Split by Leaves, Swelling Wet Debris, or Frost

Downspouts may be split and damaged from swelling organic debris (leaves) or by freezing. The result is leaks against the building wall and foundation. Keeping a strainer at the gutter-to-downspout connection will protect the downspouts from becoming clogged and thus splitting.

Split downspout due to frost (C) Daniel Friedman Split downspout due to frost (C) Daniel Friedman

Of course, if the downspout is connected to a buried drain line that is also blocked, water backing up into the downspout will, in freezing climates, still freeze and burst the downspout.

Downspout Leaks at Connections & Elbows

You might be surprised but the dislocated downspout "connection" shown at below-left is very common. Don't assume that the building's downspouts are all connected - it's worth a close look, especially if there are signs of water entry or dampness in the basement or crawl space.

Bad downspout connection (C) Daniel Friedman Bad downspout connection (C) Daniel Friedman

At above right you can see two downspouts descending the building wall. The left hand unit is leaking a bit at the elbow. The right hand downspout has lost its elbow and extension, and leakage has rotted the building wall.

Gutter and Downspout Details (C) Carson Dunlop Associates

What is the proper direction or "female" end to "male end" of downspout joints?

The sketch at left illustrates the direction of water flow off of a roof - in this case a "flat roof" that drains to two roof scuppers.

The enlarged section of downspout connections (circled detail at lower right in the illustration) explains that downspout section connections and downspout elbow connections need to be installed so that water flow will always be directed to the interior of the next or "down-slope"
downspout component.

Sketch courtesy of Carson Dunlop Associates.

Downspout Extensions that Lack Adequate Slope

Our downspout extension line photos below show what happens if the downspout extension is too flat, or if it ends aimed "uphill" from the downspouts themselves: the downspout extension simply backs up and during heavy rain, spills by the building.

The photo at below left shows a black flexible 4" drain line and tee intended to conduct roof spillage away from the building. But following the drain line we found it ending pointing "up hill".

Bad downspout connection (C) Daniel Friedman Bad downspout connection (C) Daniel Friedman

A closer look into the downspout extension connecting tee (below right) shows that the line contained standing water and was not draining.

Downspouts Emptying Below Decks & Porches

Downspout spills below deck (C) D Friedman

An often hidden basement water entry problem is traced to a downspout that the building owner thought was safely handled below an attached deck or porch.

On closer inspection we may find that the downspout spills below the deck and against the building, or that an extension has fallen off, or as we show at left, the downspout extension slopes up-hill.

Notice the water stains on the foundation wall near the downspout?

Particularly because many builders construct the deck before final backfill and grading, soil below the deck slopes back towards the building, increasing the risk of basement or crawl area water entry.

Sometimes desperate measures are needed to successfully extend a downspout out from below a deck. The photos below show a combination of a downspout that was spilling below a deck, an inside building corner, and a wet basement (not shown).

Bad downspout connection (C) Daniel Friedman Under Deck Downspout extension (C) Daniel Friedman


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