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Haag discusses buckling and splitting of asphalt shingles due to thermal expansion/contraction in their comp roof field guide.  I was recently on a roof that had severe splitting (pic attached).  The contractor claimed wind damage but changed his mind when shown the pics in the Haag guide. 

Regarding re-sealing of wind lifted tabs, there's no pricing in MSB either.  We try to agree on an amount of roofer labor required.

I observed charcoal 3 tabs cracked horizonaly in the middle of the tab(on all 3 tabs, one shingle I guess)) and it was in the middle of the 5inch tab. Not ever shingle but 15-20 (or 45 tabs) on the South slope. The  was in the the Mississippi valley. I have always thought is was caused by plywood deck movement under shingles from the freeze and thaw on bright sunny days after and ice storm or several inches of snow. I still do not know exactly what caused this but I am 100% convinced it was wind/hail...... darn it....... This was old damage I observed  while looking for hail hits.

this seal and reseal comp roof,s are myths that roofers preach. They did not start sealing roof's until the 1970's. The all use to flap. Bryan ole bud are you still a mugwomp? I am going to start another scoping boot camp, (for profit) and need an expert speaker.
(mug on one side of the fence, womp on the other),

Not that it matters, but I work for multiple companies including one of the largest national insurers. They tell me to pay what's owed, but in the event of a gray area to decide in favor of the insured and document my reasoning. It's called "adjusting".

Tabs are sealed to protect them from wind damage. Storms will break the seals exposing the tabs to future storm damage. Frequently, storm debris will be blown in under the tabs, lifting them so they'll never reseal on their own, and making them even more susceptible to future storms because they're lifted.

Along comes your local friendly roofer who has never seen a roof that didn't need to be replaced, and who tells the insured that their roof is storm-damaged and should be replaced by the evil insurance company. I explain the above to the insured and roofer and agree that the broken seals appear to be storm damage even though the shingles are intact. (Roofer now has a gleam in his eye) However, since the shingles are intact, I tell them that we'll pay to have the tabs resealed. I explain that resealing is a common procedure that will bring the roof back to it's pre-storm condition which is what we're responsible for. All the manufacturers have published procedures for manual sealing but I carry a copy of Certainteed's TIS #119 which details the methods and materials to be used.

Most insured's are happy, and the carrier is happy if the insured is happy (and it didn't cost much). I'm happy because a problem has been averted. The roofer is not happy.

Seriously?

Exactly how is this a grey area?

It's a grey area if it's a grey roof, that's how............

Or, is it gray?

I don't believe that expansion and contraction of roof decking causes cracks in shingles. 

Unless the home is more than 40 years old, roof sheathing on almost all roofs with felt and fiberglass shingles is either OSB or laminated plywood. The current standard used by most residential builders is 7/16" to 1/2" OSB on 24" centers.

Expansion and contraction of roof decking is predictable as weather conditions change. Because the sheet of OSB is nailed around it's perimeter and down the center it is less likely to move there. Where the butt ends of the sheets meet, clips are added to connect the sheets of decking together to minimize displacement. It is most likely to move in between the rafters by bowing inward toward the attic. Look at the typical modern roof early in the morning or late in the evening, when the angle of the sun is low in the sky. Some spaces between the rafters will have a shadow because the decking has drooped slightly. I have seen some severe cases.

In order for shinles to crack, either the set of nails above the crack or below the crack would need to move significantly. If the diameter if the nail hole is the same as the diameter of the roofing nail, no movement could have occured vertically to cause a horizontal crack.

Thanks Ed for your input. I have seen this more than one time in more than one city and it was always charcoal or black 3 tabs and thebottom 2 .5 inch of the broken tab was still sealed down The deck was kinda bouncy AND I just assumed it was 13/32 plywood on 2 foot truss. I never looked in the attic.The t pattern of complete breaks on 3 tabs gave me the impression only one shingle was involved.. The break was caused by the bottom 2.5 of the exposed tab being seal down so well that it could not move upward when some force was pulling from the top. Well I am still in the dark. Someone give us the answer.

Oh the shingle no more than 20 year weight and appeard to be about 8-9 years.

A google search on key words: asphalt shingles thermal movement   provides some enlightening info on the various possible causes.

http://www.google.com/#hl=en&so...bfff7f9103