A few months ago, we noticed that the roof tiles on the backside of our roof were developing many raised bumps. The roof is only 2 years old, so we called our roofer, who said that this was a "bubbling" phenomenon he's only seen once before and the last house he'd seen it on did not have enough ventilation.
The thing is that we have both gable vents and roof vents, which both the roofer and I would have thought would be ample ventilation. We do have a bathroom fan that vents into the attic, though. Is it possible that:
(1) There are TOO MANY vents in my attic, preventing the proper flow of air and trapping it in the attic?
(2) The bathroom fan that vents into the attic is counteracting the ventilation?
I can't be sure of anything without seeing the roof but I have heard the exact same story many times. In every case the shingles were defective. The installer said it was due to poor ventilation. The manufacturer asked for many forms to be filled out with lots of questions about ventillation. Many of the stories end with the homeowner hiring anther roofer to fix it. The one I like is the one where the homeowner was a general contractor and had a difficult time proving to the manufacturer that the rafters were completely exposed inside. Finally he called the outlet that supplied the shingles who immediately replaced the shingles and paid for the repair, no forms, no questions.
IMHO asphalt shingles can only bubble if they are defective. (see below) Ventilation might extend the life of your sheathing but there is no evidence that it shortens the life of your shingles nor could anyone even claim it would in so short a time. Manufacturers require ventilation in their warranties so they can have a way out in case of failure. It is routine to claim lack of ventilation first, then settle if the customer is persistant. But you won't believe how much red tape is involved. Try asking your roofer to talk to his shingle supplier. If you know someone who buys from them get them involved too.
By the way, you should not terminate your bathroom vent in the attic for other reasons, the specifics of which depend on your climate.
I looked this problem up in my favorite roofing consultant's book "Roofing Failures" by Carl Cash. The problem is called "blistering" and it can be caused during the manufacturing process by the following conditions:
1. the felt dryer on the roofing machine, just prior to the coater, was inoperative
2. the glass felts were unusually moist
3. the binder on the glass felts was incompletely cured
Last edited by mighty anvil; 10-10-2005 at 03:24 PM.