Just to add to one of the posts above about poor installation of the shingles. I was speaking with a roofer a while back and he said that many contractors use nail guns to speed up the installation time. But, many of their employees do not adjust the amount of air per shot and OVER drive the nail into the roof, sometimes punching the nail head partially through the shingle. A strong wind comes along and if the tar/glue is not adhered enough for some reason or just not strong enough, the nail pops right through the already damaged shingle and the shingle flies off. When I installed shingles on my large shed up North, I used a gun and had it adjusted to the point where I frequently had to go back down the row with a hammer and tap the nail head flat to the surface of the tile. If the shingle that came off, shows holes where the nail popped through, I bet someone had already damaged the shingle when they drove the nail in. I understand that there are different types of roofing nails too. Just my opinion as well as my two cents. I am not an expert.
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