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I just had a roof repaired (shingles replaced) because of hail damage. As far as I can tell, everything looks good. Except for one section, there's what I would only describe as a large bubble.

Are bubbles normal on new shingles, in such a way they'll work themselves out? Here's a picture, though it might not be apparent.

roof bubble

There are other soft spots in the roof, but this is by far the largest.


Thanks for responses. I got into the attic and this is what I found:

enter image description here

Uneven seam where the two pieces of plywood meet. Wood doesn't look damaged to me, though (not really a wood guy either!).

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Is it really bubbling up, or is the rest of the roof sinking down from roting plywood? Get a look from inside the attic and see if any of the plywood is turning black. – BMitch Jul 9 '11 at 2:23
@DTest, bubbles in a new (properly done) shingled roof isn't normal. Shingles should lay nice & flat on the roof. I think @BMitch could well be onto the real problem (above comment), did the weather get underneath your old shingles and soak the roof sheathing (normally OSB or Plywood)? – Mike Perry Jul 9 '11 at 4:18
Bubbles after more than a day or two of sunny weather are not normal. There is a problem under there unfortunately. – shirlock homes Jul 9 '11 at 9:29
Thanks for responses. Added an attic picture. – DTest Jul 9 '11 at 15:58
Plywood doesn't have to rot to do this, only warp. Moisture or age. Newer construction often is done with clips between the sheeting to prevent or reduce this. – Fiasco Labs Jul 8 '13 at 15:21
up vote 7 down vote accepted

Bubbles in a roof like this are NOT normal. They indicate a problem underneath. Is it serious? Possibly. It will probably decrease the life of the roof.

The shingles will have been nailed down, so this is not a case of the shingles simply pulling loose. Especially if the roof is soft there, it seems this must be a case of the plywood underneath having gotten wet and as it dried out, then warping and bubbling up underneath. The plywood should have been replaced where there were problems.

Edit: After seeing the interior picture, it looks like there was some water contact there at some time. Is it still happening, or is this old, perhaps when you had the hail damage? I find it useful to use a moisture detector - Wagner Moisture meters. It is something I have for woodturning purposes, but it is useful to resolve problems like this. You may be able to rent one, since it hardly seems worth buying one for one use though.

If there is still moisture there, it is possible that water is still getting in, that the roofer made a mistake somewhere. Water can be insidious that way, getting in the tiniest of cracks.

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Thanks for response. Updated question with attic picture. Can an uneven seam like this just be nailed down. Or will the whole piece of plywood have to be replaced? – DTest Jul 9 '11 at 16:00
This is probably not something that can be easily just be nailed down, if as is likely, the plywood has delaminated under the shingles. Possibly the plywood had gotten wet, then with the new shingles on top, the water had no place to go, so the plywood stayed wet for long enough that it delaminated. Find out if the plywood is still wet there first, if the water is still getting in. – user558 Jul 9 '11 at 18:42
It's possible it's years wet. Just bought the house in February, hail damage in April. Roof was put on yesterday and it probably got wet when they were putting the roof on, as it started raining while they were working. – DTest Jul 10 '11 at 0:10
THat being said, I don't think it's still happening. I'll try to find a place that rents a moisture meter. Thanks for the suggestion and answer! – DTest Jul 10 '11 at 0:16

This problem likely has little to do with the shingles and lots to do with sagging within the plywood decking (AKA sheathing.) I modified your picture a bit -- noise was reduced to get rid of the color/light variations coming from the shingle aggregate, and an adjustment was made to increase contrast.

enter image description here

As you can see, you have lines going up and down your roof. These are your rafters underneath, and the low points are caused by the sag in the sheathing. This causes your roof to be "wavey" and although it isn't desirable, it is not altogether rare. It does appear that that one area is slightly worse than the rest, but nonetheless, the problem isn't limited to that one specific area.

Any idea how old the sheathing is?

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Woah! It took me a couple minutes to get what you were showing, but that's some pretty cool detective work! – Zach Mierzejewski Nov 22 '15 at 15:12

It's hard to tell from the picture, but the interior shot shows what looks like water on the beam, and possibly on the plywood too. It is damp to the touch? It is significantly darker than the other wood?

As you've had the work done recently I'd call the builder back in and get him to have a look. If anything needs doing - especially if it's due to a fault in the materials or the way it was fitted - he should do it for free (or at least at reduced cost).

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I see a few issues with the interior shots:

  • moisture
  • missing h-clips between the plywood
  • rafter spacing seems too wide (though I can't quite tell from the shot)
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Respecting @DA01 mention of H-clips, an addition often dispensed with by skillfull sheathing installers (by the trick of the trade by which uniform gapping is achieved without clips):

At first I thought the sheet bowing was being dubiously attributed to lack of "edge confinement" by clips, their primary purpose being related to sheet expansion allowance. However, looking at where H-clips could have been, it also seems evident that there is no expansion gap between sheets--they seem to have been nailed down in snug fit by the original, very-likely-unlicensed, roof and shingle installer: the sheather installed panels wrong; the shingler failed to insist on correcton before felt and shingles went on.

After many (or even few) years of seasonal sheathing heat expansion, accompanied by sheet bowing and nail pulling/loosening, it would be no surprise to find loose and softened panel undulations more or less paralleling the rafters; and a good likelihood of water intrusion if shingles and paper tearing occurred...leading up to the need for (what can only be best described as stop-gap) repairs.

Since shingle roof repair is usually more difficult and more problematic than new roof, the likelihood of any recouping on account of the recent repair defects is slim to none--especially to unsheath and resheath an entire roof originally sheathed by another "roofer."

It would be a safe bet that most licensed roofers would spot such a defect and decline to do repairs--something which which roofers generally avoid anyway--for fear of "buying" a householder's existing problem or impairing his own license and bond.

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