Asphalt shingle failure mechanisms
rshuman
| Posted in Energy Efficiency and Durability on
I looked at a 13 yr old house yesterday and found most of the asphalt shingles were severely curled and, obviously, needing replacement. The roof was unvented and insulated below the deck (i.e., no foam on top) but I don’t know much more than that. The undersides of the rafters in a small storage area were covered with rigid foam. I was wondering what possible mechanisms (besides cheap shingles) could lead to such failure after a pretty short period of time. Thanks for any and all ideas.
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Replies
Rob,
The biggest enemy of asphalt shingles is heat. Asphalt shingles fail sooner in Miami than in Minneapolis. They fail sooner on a south-facing roof than a north-facing roof. And they fail sooner if they are black than if they are white.
Of course, quality also matters. Cheap shingles fail faster than high-quality shingles.
Most asphalt shingle manufacturers won't honor their warranty unless the shingles are installed on roof sheathing that has a ventilation channel under the sheathing. The presence of a ventilation channel doesn't lower shingle temperatures very much, however, so there isn't much logic to this requirement. For more information on this issue, see All About Attic Venting.
Hi Martin,
Thanks for the reply. You mentioned a lack of ventilated roof sheathing as a possible (but not probable) construction detail that could help undermine the shingles. Do any other roof construction details come to mind? I have read lots of stuff on this site about how, and how not to, insulate cathedral ceilings. Could moisture issues accompanying the placement of air-permeable insulation directly against the underside of the sheathing help hasten the demise of the shingles? I am not saying this was done, just wondering aloud. Just looking for some speculation that could help me make some decisions about the 'reliability' of the structure.
The house is located in CZ 6A, right on the coast.
Thanks.
Rob,
Q. "Could moisture issues accompanying the placement of air-permeable insulation directly against the underside of the sheathing help hasten the demise of the shingles?"
A. No -- not unless the roof sheathing became so rotten that a home inspector put his foot through your roof sheathing while trying to inspect the chimney. (A foot through the sheathing can certainly damage your shingles.)