Vertical Cracks in 3Tab Shingles

[Rick K. Kie]

My neighbor has three areas on his hip roof with 4' long cracks in the shingle running vertically from the ridge to the soffit. I have not looked in the attic, can anyone tell me why shingles would crack this way?
I am guessing snow load with 3 layers of Shingles.

[iniquette]

Sounds like sheathing may be sagging across the truss span causing the cracking possibly. Need a pic though, just a guess.

[Rick K. Kie]

I'll post a pic soon just took it! its a hip roof I dought there are trusses but i will look.

[bjones5]

Originally Posted by rkie

My neighbor has three areas on his hip roof with 4' long cracks in the shingle running vertically from the ridge to the soffit. I have not looked in the attic, can anyone tell me why shingles would crack this way?
I am guessing snow load with 3 layers of Shingles.

Not just snow load, although snow doesn't help the problem. You state 3 layers of shingles......only 2 are allowed in most states, provinces. Manufacturee's advise 1 layer only. If you read the fine print on their waranty, the roof has to be "as new" before shingling or the warranty is void. In simple terms, an old roof has to be resheeted.

[Rick K. Kie]

I walked the roof last night. there are only two layers of shingles. Lots of spotty moss buildup that could be cleaned off. I just am curious to why they would crack in this direction. There are several sections like this!
They bought the house last year and the inspector said the roof wouldn't need any work for 5 years.

[iniquette]

After seeing the pic I still say they are saggging between trusses. Where the crack is is probably a truss or rafter. Still, just an opinion right or wrong.

[rmaday]

Originally Posted by rkie

They bought the house last year and the inspector said the roof wouldn't need any work for 5 years.

Foolish statement by that inspector.

[bjones5]

Originally Posted by rkie

I walked the roof last night. there are only two layers of shingles. Lots of spotty moss buildup that could be cleaned off. I just am curious to why they would crack in this direction. There are several sections like this!
They bought the house last year and the inspector said the roof wouldn't need any work for 5 years.

If you can, get into the attic and look at the trusses or rafters, looking for any damage. Also note the absence or presence of H clips in the sheathing if the span between rafters is greater than 16" o/c.
As a sidenote, an astute observation by Mr Maday. I wonder if the inspector even went up on the roof.

[bjones5]

One other possible reson for the 4' cracking.......the sheathing may not be sitting on the rafter or truss as it should. Again, a trip into the attic may answer a lot of ???

[Rick K. Kie]

i guess I will look in the attic and report back, thanks for the suggestions.

[William M. Corbett]

Most of the time osb is 4' wide. I am with Ian. Iwould guess the cracks are in line with the seams of osb.

[Russell W. Meyers]

Rick, (Just another thought.)

When you're in the attic, check to see if it is a pre-fab house with a panelized roof system. These sysyems were typically 4' wide and would often sag between the doubled edge joints. If it is this type of system, the doubled edge joint could also be pulling apart during snow loading and causing the shingles to crack. An overall picture showing the relationship of the cracks to one another might be helpful. Definitely some structural movement / deflection taking place to cause this damage. (May be individually reinforced rafters over which the shingles are being stretched and torn when the rest of the roof sags.)

[Kenton H. Shepard, CMI]

Those splits are over joints in the underlying layer of shingles. It's a type of thermal cracking, meaning it's caused by contraction, sometimes made worse by shingles shrinking over time.

When shingles get cold, they contract and the joints between them get wider, stressing the shingle in the course above which bridges the joint (which has also contracted and is smaller). When the strength of the adhesive strip bond exceeds the tensile strength of the shingle under these circumstances... the upper shingle will split.

The joints align like that because the shingles were installed racked... in other words straight up the roof instead of offset at each subsequent course.
Racking is almost always... but not always... an improper installation.