Originally Posted By: lewens This post was automatically imported from our archived forum.
Gerry
I’m going to say none of the above. Looks to me as if the shingles were lapped under the previous row as when two workers are on the same row and one of the guys got lazy and hit the nails through the shingle instead of lifting it.
Originally Posted By: gbeaumont This post was automatically imported from our archived forum.
this can be cause by many things, but most commonly by either underdriven nails, or by being installed with nails that are too short (very common when the roof has a second layer)
Originally Posted By: jquinn This post was automatically imported from our archived forum.
Gerry,
let me guess, the nailing instructions on the bundle said "apply 4 nails per shingle...any ole random pattern will do, and they need not be applied to any shingle in particular."   
Originally Posted By: jmyers This post was automatically imported from our archived forum.
But to add to Gerrys statement:
but can also be caused by wet sheathing, trapped humidity in the attic space or by poorly ventilated attics. 
Originally Posted By: wpedley This post was automatically imported from our archived forum.
Joe M is right on track.
It actually appears to me that this roof had been replaced before
and the" heathing"was just nailed randomly, and now the nails are working their way out from humidity in the attic. Seen this before. 
