roofingshingles
I have architectural shingles. I noticed on a few of them that the some of the lower portions of the top layer of the shingle are loose, as shown.
What is this condition called? If I search for delamination, I get results about the seal between two different shingles failing.
Should I just re-adhere with roofing tar/adhesive? You can see where the original adhesive was at the bottom and mid-points of the shingle. Any other thoughts?
I wouldn't worry too much about it. The plywood is not typically supporting a load of more than the paper and asphalt shingles that were placed, even more so if you have a considerable pitch on your roof to where it would be difficult or impossible for a person to walk on. It basically serves so that you have something to nail the shingles down securely.
Most newer homes use plywood, I have an older home that used what looks like rough cut deck planks and those are mostly still original. The last time I had my roof replaced, they had to change out a few boards that were terribly dry rotted and some that were badly damaged from previous water damage by the oh-so responsible homeowners who had the home before me. Other older boards look noticeably damaged by the most recent nails but they continue to hold down the shingles and I would still feel safe to stand on my roof.
As long as the shingles are doing their job then the plywood will not be exposed to any water, and as long as your attic has good ventilation during the summer time then you should have nothing to worry about for the next 15-20 years at least.
In brick/masory homes the vertical slots are called weep holes.
Their purpose is to allow the rain water that soaks through the brick to come back out. From what I learned, about 10% of what gets on the brick passes through since the brick is porous. On the back side of the brick there is a drainage plane, or surface that has been traditionally tar paper nailed or stapled over the wood framing. The paper is lapped so the water as it collects goes over the laps and continues down where the through wall flashing turns it back out the wall through the weep holes.
7-28-2018 edit
I just re-read the question and seen I really did not answer the question at all. The horizontal gap is typically not there. as Lee Sam mentioned, counter flashing should be there, but I hope is still there deeper inside the recess.
For some reason the builder decided to set the brick on a steel lintel (beam of a sort) above the roof, instead of below the roof where this space would not be seen. If the through wall flashing allowed it, typical counterflashing could still be applied although there would be no backer for it. Backer would keep it in a vertical plane. As a mention counterflashing is used to cover the base flashing that is covering the tops of the last row of shingles.
This sketch is not the only way to do it, but it is the best way to do it, IMO. The problem is, the potential to damage the all important through wall flashing is quite possible (the black line behind and under the brick).
To simply fasten something on top of the shingles for the sake of holding something in place to hide the gap would also have a strong possibility of making leaks in your roof.
Best Answer
Its delaminating like you said! The shingle is made of two mats that are adhered together giving the shingle its dimension! This is a manufacturer defect and more commonly happens on steep or mansord roofs! You can try and make a claim with the manufacturer if you know what kind of shingles you have! Best thing is get a couple tubes of roof cement and put a dab under any loose spots so they don't end up sliding on you!