In their April 2011 Steep Slope Technical Point Newsletter, GAF addressed damage to shingles from gutters and downspouts when runoff is left unchecked.
When gutters and downspouts from an upper roof spill out onto a lower roof, damage can occur to fiberglass-asphalt shingles. They note:
- Erosion Occurs: The shingle grit on a shingle’s surface can erode under a gutter outlet or downspout. Erosion might be visible in 1-2 years (or less) or potentially be less severe, all depending on the amount and force of water being discharged onto the shingles. Erosion wears the surface of the shingle, eventually exposing the asphalt, causing premature aging and a shortening of the shingle’s life.
- Leaking may result: If the water spilling onto the roof is forceful or high volumed, it may be strong enough to get in between the shingles, causing a roof leak. Depending on the conditions, it might take years to notice the leak inside the home and, by the time it’s noticed, extensive damage might be found on the roof deck, insulation and ceiling.
- Organic materials may grow: with a higher moisture environment created under a downspout or gutter outlet, shingles underneath will likely dry less quickly than the rest of the roof, creating an environment where moss, mold, fungus, algae or other vegetation may grow. This type of vegetation can damage the roof or building.
- Walls can be damaged, too: Water discharged near an exterior wall can have it’s own problems. Water can cause wood rot, cause flashing to fail or mortar to deteriorate. The cost to fix issues related to water damage can be expensive.
Shingle Damage by Gutters & Downspouts
GAF Report on Gutter & Downspout Damage
Taking these issues into account, this newsletter notes damage to GAF shingles from loss of shingle grit or erosion due to gutters ad downspouts draining onto lower roofs is not their responsibility under the Terms of their Limited Warranty.
Since water management is so important, what can be done to address the issue? MasterShield recommends one of our own installation methodologies:
- Don’t filter the water twice: Once the water has been collected in the gutter protection system, make sure it stays contained through a downspout linked into a lower gutter or into a longer downspout routed directly to the ground.
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No one wants to cause premature aging to their roof. That aside, it's also uncommon or unpopular to install gutters and downspouts that link to lower gutters. Given that it may affect your roof warranty, it may be something worth reconsidering to offer additional protection for your home.