Definitely a shingle defect on the caps as the roof shingles next to the caps show no problems or premature deterioration. Our roofs really do not get “overheated” as they are (or should be) designed to withstand the temps expected at the top surfaces (especially where much hotter down south where surfaces temps can be 150+*F).
Venting barely affects the temperature at the outer surfaces which receive the direct sunlight. One study done by Building Science Corp in Florida showed only 2-3F temp rise in shingle surface temps with unvented attics under them. How can a 2-3F shingle temp rise be the cause of shingle failure for a shingle that may operate in a seasonal temperature regime of freezing to 100+*F??
When is an attic overheated?
It has been claimed by some on this board that they have measured attic temps of over 160F in attics down south…and this is with venting! Up here in temperate Nova Scotia, unvented attics will only get in 110-125F range, yet folks claim these attics are overheated and will severely shorten shingle life!!
Before the addition of insulation in attics, there was little deliberate venting of attics. These houses had asphalt shingles and no manufacturers were claiming the unvented attics were ruining their shingles prematurely.
With the addition of insulation to attics, the spaces above the insulation now became cold and if you had a wet/damp house below with no airsealing at the attic level, warm moist air rising from below would condense on the now cold roof boards. Adding ventilation in most cases** would cure the condensation. So ventilation eventually became part of better building practice and codes. Somehow, shingle manufacturers jumped on the bandwagon claiming the ventilation was also needed to save their shingles from overheating.
Dr. Bill Rose (Phd building scientist at U of Illinois) says that manufacturers are hiding behind the venting requirement to save themselves from lawsuits (and there are many if you do a GOOGLE search) due to poor shingle quality. Remember the price of oil 10 years ago was down to $10/barrel…asphalt was cheap. In one month, January, this year, the price of asphalt went up 20-25%…in a period with the least demand for it!!! We have seen many, many pictures of shingles with premature deterioration on this website . SO, we should be putting the blame where due, the manufacturers, and remember that lack of venting is not the main cause of premature shingle failure!!
** About 2 months ago, I consulted to government here on a house in their low income energy retrofit program. It had a severe attic condensation problem in the first winter (08-09) after being blown with cellulose fiber (walls + ceilings)in summer 08. The owner (an older widow and only occupant) consulted with both a roofer and a local code inspector in summer 09. Both told her she needed more attic venting, which she had installed last year.
During this past winter, which was a mild, warmer winter here (March had 2-3 weeks of May temps), she felt the house was colder…and she had a worse attic condensation problem!!!