Buckling shingles

[scottzilla]

You can see a bubble forming under my shingles and if you look closely there is a wavy secton of shingles running up the roof.

The black streak to the left is what's commonly referred to as roof algae.

The bubble does not seem to get worse when it rains and there doesn't seem to be any water intrusion (I cannot see the bubble from the inside because the spot is behind an attic knee wall).
Here's another pic.

Anyone know what causes this? Roof is 12 years old.

 

[srmofo]

is the roof vented properly?

is is the shingles popping up like that or is the decking underneath it popping up?

 

[NUTTSGT]

My first guess would be plywood sheathing that is separating.

 

[Mantown]

nail backing out

 

[reptilezs]

improper nail pattern

 

[OldmanB]

Impossible to tell,unless you know what's under the shingles

 

[Mister Moose]

Maybe stating the obvious, but why not get out a ladder and take a look under the bulged shingle?

 

[kbs2244]

From here it looks like delaminating plywood.
Most likely due to not enough venting installed when they put in the knee wall.

 

[signcrafter]

Based on what you said, "behind a knee wall so you can't see behind it", I would go with improper venting which led to sheathing delaminating. How is the space behind your knee wall ventalated? Soffit vents, ridge vents, roof vents, gable vents? The best way to vent something like that is soffit vents to allow air into the space behind the knee wall, then use foam baffles stapled to the underside of roof sheathing where(I'm assuming here) that the interior is drywalled up to the "attic" space above the ceiling and then that space vented using ridge vent. If you don't have good venting in the space behind the knee wall and have been having hot weather like most of the country it can cause major problems like this. That space is like an oven with the sun shining on dark shingles all day reaching temps well over a hundred plus. Try and find out how that area is vented. If this is the case and the interior is finished it can be an expensive fix. The easy fix would be to try and cut some vents in the roof or the gable ends. But that probably wouldn't be the right way to fix it depending on a bunch of things.

 

[SARG]

Replaced several sheets of "buckled" plywood last year & it looked just like your picture.

The sheathing had become wet because of a stove vent that had become loose and vented moisture into the area.

 

[Gary S]

Replaced several sheets of "buckled" plywood last year & it looked just like your picture.

The sheathing had become wet because of a stove vent that had become loose and vented moisture into the area.

Quite possible ^..

The first thing I would do is go up there and step on the bulge. Does it feel like just the shingles, or is some part of the roof causing it? I'd almost bet on the roof.

Plywood has a bad habit of doing things like this when the layers decide to delaminate, or when you get some moisture in it. If you have plywood there, it is a good suspece.

I much prefer OSB for roofs and walls because it is usually more stable in the long run.