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This article describes defects in roof leaders or downspout systems such as inadequate number of downspouts to handle the volume of roof drainage, missing, lost, or damaged downspouts. 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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Also see DOWNSPOUT LEAKS or start this topic at DOWNSPOUT / LEADER DEFECTS; also see GUTTER DEFECTS LIST for other sources of wet basements or crawl spaces caused by problems with the roof drainage system.
Our photo of an upper roof with no gutter (below left) shows how seriously water splash-up may stain or affect building walls. Not shown (not visible) in that photo is wear on the roof shingles from water splashing from above. Our photo at below right shows algae growth on shingles from a downspout spilling across roof shingles.
We often see early roof shingle wear, staining, or even roof leaks on lower roof slopes in areas where drainage from an upper or secondary roof slope spills onto the lower roof slope.
Sketches in this section courtesy of Carson Dunlop Associates.
A solution to the wear problem caused by spillage from upper roof slopes onto lower roof slopes is the installation of gutters on the upper roof slope combined with a downspout to conduct that upper gutter's drainage contents directly into a lower roof gutter or even directly to the ground.
Watch out: in the illustration shown if the splash block does not conduct water far enough away from that basement walkout stairwell water may cause damage to the stairwell sides.
Especially in freezing climates we often see frost heaves and collapsing concrete block stairwells that have been exposed to main roof or small auxiliary roof water runoff.
Sketch courtesy of Carson Dunlop Associates.
As we've stated earlier, a rule of thumb is to install a downspout for every 35-40 feet of length of gutter. But there are some other considerations to keep in mind.
If the roof design prevents good gutter slope (less than 1" of gutter drop in 200" of run) then adding more downspouts can help prevent gutter overflow in periods of heavy rain.
Adding more downspouts (and larger gutters) can reduce the frequency of gutter overflow due to clogging on roof slopes close to trees, especially pines and firs whose smaller needles wash into and clog gutters and screened gutters.
More downspouts will be needed for discontinuous runs of gutters along irregular roof eaves or slopes.
Sketch courtesy of Carson Dunlop Associates.
Use of strainers both helps and hurts with the downspout and gutter clog and overflow problem.
Installing a strainer in the gutter where it empties into a downspout helps keep the downspouts clear of debris and clogs. As Carson Dunlop point out, the gutter itself will clog more quickly with a strainer installed however.
Watch out: if your downspout system includes buried lines, clearing a clogged buried drain line can be difficult and expensive. For buried drain line systems we recommend that you always keep strainers installed at the downspouts at the gutter drain points.
[Click any image or sketch to see an enlarged, detailed version.]
It's usually easier to clean the gutter than to clean the buried downspout drain line. Sketch courtesy of Carson Dunlop Associates.
Our photos below show unusual downspout extension damage - doesn't it look as if something has "chewed" the aluminum downspout ends? in fact that was just the case. The building owner explained that when a squirrel or other rodent entered the downspout the family dog became quite excited by the animal's noise or odor even though the humans were unaware of their visitor.
The dog, frantic to get to the now trapped animal, tore up the downspouts with its bare teeth. The second downspout dog bite photo (below right) was the same phenomenon observed at a different property. More than one dog with strong jaws finds downspouts interesting.
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