What caused this roof failure?

[KAlmquist]

House was built in 1966. The roof was redone in 1994, with Bird Mark 80 fiberglass shingles placed over the original shingles.

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The roof sheathing is 5/8 inch C.D. exterior grade plywood (presumably CDX plywood in modern parlance). I'm guessing the deformation is due to water damage. This roof is over a cathedral ceiling. Water is entering the exterior wall of the house, and since there are no obvious problems with the siding or the rest of the roof I'm guessing that the water is penetrating the roof at this point, running along the interior of the ceiling and into the wall.

Was the flashing done correctly?

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[Bill Kibbel]

Was the flashing done correctly?

When the second layer of shingles was added, they did not re-install or replace the flashings at the chimney. They just threw on the new layer and caulked the joint. The leak and damage appeared after their check cleared.

It's wrong - and now there's considerable damage to the sheathing and probably adjacent materials.

[KAlmquist]

Thanks for the reply, Bill. Curiously, it looks like they did reinstall the flashing on the other side of the chimney (at least they got a shingle under it).

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[Marc]

I'd place blame for the rotted decking on a combination of things...poorly installed flashing, poorly constructed chimney cap and last but not least, the double layer of shingles.

I haven't read anything on how multiple layers of shingles ends up damaging the roof deck. Instead, I've seen it with my own eyes and fixed it with my own hands. It holds moisture well.

Marc

[Jerry Simon]

I haven't read anything on how multiple layers of shingles ends up damaging the roof deck. Instead, I've seen it with my own eyes and fixed it with my own hands. It holds moisture well.

Must be a regional thing (humidity?). I've walked thousands of roofs covered with multiple layers of shingles, and unless flashing or some such is leaking, I can could probably count on one hand the number of soft roof decks I've found.

[Eric B]

What's the chimney used for?

What is the condition of the flue liners?

Is the roof properly vented?

Is the water problem only at this end of the roof?

[KAlmquist]

What's the chimney used for?

What is the condition of the flue liners?

Is the roof properly vented?

Is the water problem only at this end of the roof?

The flue on the left is connected to a wood stove, the middle flue is connected to an unused fireplace, and the flue on the right is not connected to anything. I don't know enough about chimneys to say anything intelligent about the flue liners.

The house has soffit and ridge vents.

The only place I've encountered water in the house is at that end of the roof. There is what appears to be a water stain in the ceiling closer to the other end of the house, but I don't know how old it is.

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[Charlie R]

In at least one photo, there is some shattered brick on the roof. This indicates moisture in the brick chimney from the bad chimney cap already mentioned. Look around the interior, especially inside that unused fireplace for white stains (efflorescence) which would be evidence of water intrusion from the cap also. Water damage to the sheathing is probably from the flashing but some could be from water getting into the bricks too. Needs a good roofer and a good masonry contractor.

[Eric B]

Kenneth, All you can really do is speculate right now. And honestly, do you even know if the staining represents a current moisture problem? You said that there are soffit and ridge vents but is there actual air flow through each rafter bay? Until an invasive evaluation is done all analysis will be nothing more than guessing. As an inspector I might mention (verbally) some possible causes but I wouldn't be pointing anyone to any specifics. The last thing you want is someone wearing blinders because of something you said / wrote.

[John Kogel]

The old stains are probably from when the roof leaked before the reroof.

We know the owners were cutting costs because they had the new roof laid over the old. So likely the old roof leaked for a while as well before something was finally done.

I suggest the chimney flashing was already leaking in 1998, so the sheathing was wet. The roofers slapped a new layer on and trapped moisture where the old roof was leaking. Then it looks like the flashing continued to leak in that area. It all needs to be fixed properly.

[Tom Raymond]

I suggest the chimney flashing was already leaking in 1998, so the sheathing was wet. The roofers slapped a new layer on and trapped moisture where the old roof was leaking. Then it looks like the flashing continued to leak in that area. It all needs to be fixed properly.

That's my guess, and the chimney is a newer and seperate issue.

[jimd4j]

I agree, it's all speculation with out removing the shingles, the sag in the roofing point to a installation job with the sheeting, did they run out of moisture barrier? when you get down to the sheeting check where the seams run along with moisture penatration a miss placed seam can lead to a lot of problems.good luck ,saving$ sometimes leads to poor preformence.