# Split laminated shingles

Recently inspected this roof with diagonal split lines in the top layer of a laminated shingle off the corner where a single story roof wrapped around a two story corner.
The roof is a low slope, 2/12 maybe, over an un-heated screened in porch, partially running over a 4/12.
Any ideas what would cause this and how to comment on it. Only area in roof where this was noted.
Location, Northern Michigan.

I’ve seen roof shingles, stuck to the roof from ice damming, get damaged like that when someone has tried to pry the ice off.

The Haag field manual has photo with same fault and it describes the cause as moisture or temperature related causing expansion of the decking. The shingle is fixed in position and the moving deck splits the shingles. The diagonal line is caused by the forces which are highest on the longest vector which shows itself as a split line at 45 degrees to the horizontal and vertical forces (vectors).

Mark, can you put the last sentence in simplier english?

Sorry James I’m using an iPad in a conference. I’ll be back tomorrow with an illustration that I hope will make it clear.

Seeing it is in Michigan i would say scraping ice off , could be the deck issue doesnt really matter, Damage shingles , recommend repairs

in sim-plier

that dang diagonally splitting force occurs across the 8’ length of the 4x8 sheathing ;~))

Thank you Barry for the simpler sentence. If you look at the diagram you can see the two main forces at work; F1&F2. (Formula not shown) The forces are highest at the corners of the shingle at an angle F3. Result is a split as seen on roofs from time to time.

Thank you Barry for the simpler sentence. If you look at the diagram you can see the two main forces at work; F1&F2. (Formula not shown) The forces are highest at the corners of the shingle at an angle F3. Result is a split as seen on roofs from time to time.

Thanks Mark! It makes sense now, and even more sense the way Barry explained it.

Santa’s sleigh, hard landing.

P.S. A better description would be “asphalt 3-tab shingles”, not “laminated”.