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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.

UPDATE:

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, 2011 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, 2011 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, 2011 at 9:29
  • 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, 2013 at 15:21

6 Answers 6

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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?
    – Derek Downey
    Jul 9, 2011 at 16:00
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    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, 2011 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.
    – Derek Downey
    Jul 10, 2011 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!
    – Derek Downey
    Jul 10, 2011 at 0:16
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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, 2015 at 15:12
  • That is amazing photo work. I wish I knew how to do that...
    – Lee Sam
    Mar 1, 2017 at 3:36
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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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I vote your builder as the worst in America. If you look at the pic "from below" you'll see that: 1) the truss spacings vary, 2) the shingle nail spacing vary, and 3) I'm betting you don't have enough attic ventilation.

1/2" Plywood roof sheathing can only span up to 16" (in some areas of the country with little or no snow, that spacing can be increased due to what is called, "short duration loading".) That one truss spacing looks like more than 24", in which case you need 5/8" min. (By the way, I like five ply for that.) I'll bet he used 1/2" plywood and spread the trusses apart for some reason, (I.e.: miss a chimney, etc.). I'd talk to the Building Inspector about that.

From the bottom view, you can see the shingle nails are all over the place. They are not "in line" and the spacing goes from a couple of inches apart to an area where there are maybe 2-3 nails per shingle. That is not allowed by ANY roofing manufacturer. They are suppose to be uniformly spaced. No wonder the shingles are buckling. (Oh, if you want to check a really obscure thing, check the distance from the butt (bottom) of the shingle to the nail. Read the wrapper (or go on line and read the "nailing instructions".) Few roofers actually nail in the correct "line". This is important because it will warp the shingle where the nail penetrates the 2nd shingle below the exposed shingle and cause a leak. Also, check to see how many nails are required in each shingle...I'll bet it's 5, unless you're in a "high wind area", then 6.

You need 1/150th the area of the house for CROSS ventilation. Or, if you place 50% but not more than 80% in the top of your roof (ridge vent or gable end vent) if it's more than 3' above the eave, then you can reduce the amount of ventilation required to 1/300th. It looks like you have a ridge vent, but I'd check the eaves. I'd bet it's way too low.

How much did you pay for your Building Permit, which included inspections? You got robbed.

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