Asphalt shingles diagonal cracks 1

[smb4050]

I saw an unusual problem and I'm wondering if anyone else has. On hail damaged asphalt shingle roof, diagonal cracks at 3 foot spacings can be seen in the shingles. See attached photo. When on the roof, there are more cracks than can be seen in the photo. The cracks aren't due to hail damage, so what cause them. To me the logical cause is due to torsional loads (wind)on the building, but why did the shingles crack and not the sheetrock ceiling? There are cracks in all 4 roof sides, and they change directions indicting a circular pattern. One interesting point is on one roof side the cracks run one direction at one end and the opposite direction at the other. It's possible the ceiling could have been fixed. I'm questioning if the cracks are the result of a manufacturing defect or cheap shingles? It's a smaller wood framed building, 50' x 61' x 9', with slab-on-grade construction built in the early 1990's. The roof is a hipped roof with a 5:12 slope, pre-manufactured trusses @ 24" c-c w/ 2x6 top & bottom chords and 4' overhang. It has 5/8" cdx roof sheathing. Over all the building looks petty solid, but fastener type and spacing for wall or roof sheathing is unknown. This isn't a complex building or an expensive problem, but I haven't seen it before and I find it interesting and thought other engineers might also. Thanks,

 

[ToadJones]

well, here is my opinion.
I have installed many 'a roof myself over the years.

It appears that the cracks are on the third tab of a three-tab shingle.
I think this is directly related to the installation technique.
Although it is not recommended by most manufactures, some roofers will lay the shingles straight up the roof in 3 foot wide passes rather than "pyramiding" the shingles.
This causes the roofer to lift up the last shingle on the end as he makes his way up the roof with each successive coursein order to slip the next shingle underneath.

 

[ToadJones]

Could very well be shipping damage as well. Like something bashed the edge of the bundles.

 

[dhengr]

Toad:
I generally agree that it is most likely an installer caused problem. But, they do not all appear to be on the right or third tab. Could these corners be flexing over a high nail head below?

 

[Ron]

TJ..I agree. You nailed it (ok, ok...bad pun). I also noticed it was on the last tab of the three, so was more likely related to installation than manufacturing. I also wondered if it was a possible roof-over as was popular for a while, but the shingles look too flat for a roof-over.

If it was built in the early 1990's, it is about time for a re-roof. The striations in the shingle indicate a loss of granules on the areas that were likely bent up during installation as TJ noted.

 

[msquared48]

This is not the sort of problem to get bent out of shape over here guys. Just blame it on the Architect!

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Ron]

Mike...I like that!!

 

[ToadJones]

getting back to the original post, I would say that torsional wind loading being the cause is very far fetched. It's a far-reaching conclusion. To say that the torsional deflections of the building were so consistent and manifested in such consistently cracked shingles is actually almost comical...I DO NOT mean any offense by that.

Also, while unsightly, these cracks will not cause a leak because of their location.
That roof has already seen the better part of its life. Most shingles of that time were 20 yr warranty and the high end 25 years.
Ron can probably verify the previous statement.

Ron also may have more input, but I have been called to some "hail damaged" shingle roofs (sister is an insurance agent). They were all after local storms widely covered by local media. It amazed me that nearly every single one of these "hail damaged" roofs was already 10 yrs past the time when it should have been replaced, in a terrible neighborhood, and owned by a customer a few months behind on their insurance premium.....I'm just saying (-:

 

[Ron]

I agree again with TJ...the shingles have probably seen their better years go by. If there was hail, it probably only removed granules at a higher rate in the areas where the shingles had been previously strained by bending.

Agree also that his has nothing to do with the structure, structural movement or wind loading.

 

[smb4050]

I didn't think of an installation issue, but it seems logical also. These are not the original shingles. When I asked when they were installed, and the owner didn't know as he bought the building 5 years ago and it was before that. This isn't a reroofing and I didn't see any high nails. The shingles looked flat and well fastened. The cracks continue for several rows always on the diagonal so I don't think they were installed in a striip. My bad for not checking if the cracked tabs were at the end of the shingles. I've got more photos so I'll go back and see if I can tell where the shingles butt.