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Old 12-17-2010, 09:17 PM   #1
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New Bulge Under Shingles


I was up on the roof today for the first time since winter has begun and I noticed a strange bulge that was not there a couple of months ago. It's about 2 1/2 feet long, a foot wide and rises a couple of inches. The whole area feels solid. The roof is two layers of 3 tab asphalt shingles over an OSB deck. The attached picture is as clear as I could make it. I will be re-doing the roof in the spring, but before then I am wondering what the hell is going on. Anyone know? Thanks.

(the bulge stretches across the middle of the pic)
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Old 12-18-2010, 02:03 AM   #2
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Could be the tar paper rolled up at a seam.....water penetrated and froze, causing it to heave. Melted away in the thaw and left you with a nice "lump". You'd be surprised at how sturdy rolled tar paper can feel.

Good luck!

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Old 12-18-2010, 09:31 AM   #3
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It's your OSB racking at the joints.
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Old 12-18-2010, 09:47 AM   #4
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could be some water has been getting in around that chimney flashing..?
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Old 12-18-2010, 11:01 AM   #5
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Whatever sheeting you replace, use plywood, not OSB.
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Old 12-18-2010, 12:10 PM   #6
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Why Rusty?
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Old 12-18-2010, 02:20 PM   #7
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Because beaver barf (OSB) falls apart when wet. It's not as bad as partical board but still should not be used.
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Old 12-18-2010, 08:22 PM   #8
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Thanks for the input. I imagine I should plan on replacing all the OSB? This roof project is getting better and better.
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Old 12-18-2010, 09:39 PM   #9
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OSB is used all the time as an underlayment with no problems. Yours is not a material issue. Install anything too tight and when it expands it's going to buckle like that. This is why they tell you right on the product to leave an 1/8" gap
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Old 12-18-2010, 10:24 PM   #10
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Quote:
Originally Posted by OldNBroken View Post
OSB is used all the time as an underlayment with no problems. Yours is not a material issue. Install anything too tight and when it expands it's going to buckle like that. This is why they tell you right on the product to leave an 1/8" gap
I agree OSB is used all over the country for roof decking it is my opinion that it is missing an "H" clip and now starting to buckle I would leave it alone (provided it does not get any worse) since you are going to replace the roof in the spring. and once the shingles are off it will be an easy fix.

Good Luck
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Old 12-19-2010, 12:01 AM   #11
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It appears the leak is above and closer to the chimney flashing, hence the second ripple there.

Osb is inferior to plywood mostly in it's drying ability after wet. Not recommended for walls in your City: http://www.google.com/url?sa=t&sourc...JSz4eA&cad=rja

Or around a Coastal area: http://www.coastalcontractor.net/cgi...ticle.pl?id=14

It will probably hold that shape: http://alcor.concordia.ca/~raojw/crd...say000292.html

As said, the gap is not there, installed tight without an "H"- clip: http://www.buildingscience.com/docum...d%20in%20walls

Sorry to depress you further...... http://www.ewpa.com/Archive/2006/aug/Paper_266.pdf

Gary, South about 35 miles
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Old 12-19-2010, 06:23 AM   #12
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Quote:
Originally Posted by GBR in WA View Post
It appears the leak is above and closer to the chimney flashing, hence the second ripple there.

Osb is inferior to plywood mostly in it's drying ability after wet. Not recommended for walls in your City: http://www.google.com/url?sa=t&sourc...JSz4eA&cad=rja

Or around a Coastal area: http://www.coastalcontractor.net/cgi...ticle.pl?id=14

It will probably hold that shape: http://alcor.concordia.ca/~raojw/crd/essay/essay000292.html

As said, the gap is not there, installed tight without an "H"- clip: http://www.buildingscience.com/docum...d%20in%20walls

Sorry to depress you further...... http://www.ewpa.com/Archive/2006/aug/Paper_266.pdf

Gary, South about 35 miles
I reread to OP and he doesn't mention a leak, am I missing something?
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Old 12-19-2010, 08:51 AM   #13
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OSB does not bow like that. It swells if anything when it gets wet. Plywood bows just laying flat on the ground. Although any board will bow without the proper spacing.

GBR, that first link is for walls that have no vapor barrier, not vented roofs.

I'll use OSB every time over plywood.

I haven't seen a pic of the OSB board from the OP yet.

Here's a good link http://bct.eco.umass.edu/publication...d-and-plywood/

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Old 12-19-2010, 11:36 AM   #14
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Yeah, I'm thinking your problem may be originating from that chimney also. It's not the sheet bowing in the middle, it's the joints racking.
Seems like an awfully old roof to have two layers AND osb under it. Then again, you do live on the rusty side of the state.

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Old 12-19-2010, 06:56 PM   #15
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I presumed there was a leak at the missing cricket or upper corner flashing, not the first time I would be wrong..... I've had OSB bow the 10' edge studs right out/off the wall, with a gap installed, after much rain. Inspectors around here have made the framers cut the gaps at the sheet edges, if left out. Just not my favorite product as it dries out slowly compared to plywood.

MJW, I did state walls for that link, read it again, slowly. Just showing what I think of that smelly (formaldehyde) product after 30 years of installing it professionally on walls and roofs since it came around in the '80's. (No choice)

“Irreversible edge swelling has been the biggest knock on osb. Manufacturers have done a good job of addressing this issue at the manufacturing facility and during transportation by coating panel edges. But the reality is that builders don’t limit osb use to full-sized sheets. The edges of cut sheets are seldom if ever treated in the field. Houses under construction get rained on. And if you use osb in an area of very high humidity, like over an improperly vented attic or over a poorly constructed crawlspace, you are asking for trouble.
Osb responds more slowly to changes in relative humidity and exposure to liquid water. It takes longer for water to soak osb and conversely, once water gets into osb it is very slow to leave. The longer that water remains within osb the more likely it is to rot. Wood species has a significant impact. If osb is made from aspen or poplar, it gets a big fat zero with regard to natural decay resistance. Many of the western woods used to manufacture plywood at least have moderate decay resistance.” From: http://bct.eco.umass.edu/publication...d-and-plywood/
OSB and plywood are about equal except when wet. Plywood (2.7) has almost twice the vapor permeance of OSB (1.5) and 10 times the moisture diffusivity: Chart: http://alcor.concordia.ca/~raojw/crd...say000129.html

We can only guess at the problem until the OP wants to remove the shingles. I would check the chimney carefully. I agree there was no gap but also think water is involved. My 2cents…..

Gary

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