What causes this?

What copperman and tinner said . . . we replaced a roof on GAF's dime also. Late 90's was when the original roof was installed, so seems like the problem was confined to that time period.

I seem to remember that it was the GAF Timberline that started the dimensional line. We had a 25 year Timberline installed on a church. They were organic construction at the time, and they didn't last 15 years. Loss of granules was pretty dramatic.

I think CT was first but here is GAF patent.....

http://www.freepatentsonline.com/4717614.pdf

Mike H Said: but I dont think dimensionals were even in existence then??? Three tabs and T-locks, only shingles I ever did. Your explanations make perfect sense.

Does anyone remember what year dimensionals came out in? - and what brand? I know when I put my roof on in 1985, they were pretty fresh on the market. Maybe very early 1980's? And I think it was GAF that lead the charge with Timberline. They were originally made with their back laminate piece offset of the main body by about an 1/8" of an inch or so; so that they overlapped a bit at each butt seam.

I installed a Johns Manville dimensional shingle on my house in 1985. After 13 yrs., they had split / ripped speratically all over the roof (too much stabilizer used in the asphalt mix!). I filed a claim with Johns Manville and a Rep came out and claimed it was deck movement (fortunate for him that I wasn't home at the time or else he would have found himself thrown off the roof). The felt paper was still fully intact at the places I had removed the shingles! Thank God J.M. doesn't make shingles anymore!

On the other hand, I did a replacement roof on a church and you could tell it was deck movement. The cracks were all lined up with a 4x8 sheet of plywood. You could see almost every outline of the plywood. There was no ventilation installed on this Stress Panel roof. After stripping the shingles, we added firring strips 16" o/c and another layer of OSB.

Pull a few shingles and see what the condition of the underlayment is like, and then see where the seams of the roof deck are at. This will definitly tell you what is at fault.

Well here in the great white north, i've seen that many of times. Usually you'll see it in new construction. That being said, It's the expansion and contraction of the foundation. The ground will freeze then thaw, letting the foundation settle. Transfering that to the roof line. The crack is way to vertical to be a Timberline problem. It's structual."COPPERMAN" makes a point.

Cool. I love the days I learn something worth learning. Thanks Copperman and Tinner.

I learned to shingle by racking, with all nails installed of course, but I don't think dimensionals were even in existence then??? Three tabs and T-locks, only shingles I ever did. Your explanations make perfect sense.

Thanks guys.....I kind of figured it was a defective shingle. This house was built in 1998.

There are about 4 or 5 of these cracks. The shingles are racked and the cracks are from the eave to the ridge, if you notice.....the cracks are in a perfect straight line and are where the shingle seams meet. These cracks are 22' and almost a perfect line. The decking is staggered, no interior cracks and roof decking feels very solid.

Thanks!

I've seen it often. In each case, the common denominator was the sealant holding tightly, AND the end nail was not in every other shingle at the split. They always happened within a few inches of a joint where the shingles were staggered back and forth straight up the roof, and a nail was skipped.

They are the old GAF Timberline shingles. they had a recall years ago on them after a class action law suit. what happen is the seal down cement was to aggressive and did not allow the shingle to expand so they ripped up in straight lines like that. I replaced many of them on GAF's dime

im not a shingle roofer, but that looks like a stress fracture. did they stagger their seams on the decking? almost looks like they didn't.

Looks to me that whatever was holding the roof up on the left side fell in. We had a situation once(w/o that weird crack) where we thought he had a leak that fucked up the sub/fascia but his supporting post had sunk into his flower garden and left that portion of the roof sunken in. Thats weird though, any inside damage?