# OSB sheathing troubleshooting.



## RMcBride (Dec 21, 2009)

Greetings:

We are having a call-back issue on one of our houses. The 7/16" OSB sheathing on the sides of the house is buckling so badly it had caused the vinyl siding to unzip itself. We frame with 2x6 studs, 24" O.C. and cover them with 7/16" OSB and then half inch dow blue foam board. 

The OSB is nailed on correctly, but is bowing out from the house between studs a good 4-5 inches.. We cut a small section out and found zero moisture behind it: the insulation, drywall, OSB - all bone dry. The attic is venting correctly and there are no other obvious signs of trouble.

Any thoughts?


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## Framer53 (Feb 23, 2008)

RMcBride said:


> Greetings:
> 
> We are having a call-back issue on one of our houses. The 7/16" OSB sheathing on the sides of the house is buckling so badly it had caused the vinyl siding to unzip itself. We frame with 2x6 studs, 24" O.C. and cover them with 7/16" OSB and then half inch dow blue foam board.
> 
> ...


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## Fence (Mar 5, 2010)

...


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## JonM (Nov 1, 2007)

Sounds like the OSB got wet somehow...:thumbsup:


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## RMcBride (Dec 21, 2009)

We checked everywhere - it was installed during our dry months - covered with the foam the day after it was hung. No sign of moisture on the outside or inside. Insulation is bone dry as is the drywall.


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## Framer53 (Feb 23, 2008)

RMcBride said:


> We checked everywhere - it was installed during our dry months - covered with the foam the day after it was hung. No sign of moisture on the outside or inside. Insulation is bone dry as is the drywall.


I wonder if the OSB had cured when you used it. I still bet you got some bad OSB. 

Have you contacted your supplier?


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## RobertCDF (Aug 18, 2005)

Just saying... I doubt it would have happened on 16" o.c.


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## PrestigeR&D (Jan 6, 2010)

*Rob's point*

That's what i was thinking 24" oc Could it really be the OSB? 
Brian


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## Kgmz (Feb 9, 2007)

Which way did you hang the OSB, vertically or horizontally?

OSB does have a strength axis and some sheets are designed to hang vertically and some are designed to hang horizontally.

What does the stamp on the back of the sheet say? You will see the strength axis on the stamp.

Also did these sheets have those painted lines on them to show 24" or 16" O.C., were the lines running the long length or the shorter width of the sheets. Those lines also show the strength axis.


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## Warren (Feb 19, 2005)

Did you gap it properly?


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## BKFranks (Feb 19, 2008)

Did you maintain a 1/8" spacing between panels? All the OSB manufacturers I looked at call for it.


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## Kent Whitten (Mar 24, 2006)

If it was installed bone, bone dry, then moisture could still be the culprit. Say it came from the factory overcooked, you installed it in the driest of dry months, and used the OSB that has SYP chips in it, then once the water vapor gets to it, it is quite possible to buckle, especially 24" OC. 

What about the orientation of installation? H or V?


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## JT Wood (Dec 17, 2007)

Are you saying the osb is buckling out 5" between studs?

Are the studs all true?

Your 8' sheet would be like 8'3" if it had that kind of bowing


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## loneframer (Feb 13, 2009)

Gapping the sheets on ALL sides is crucial, regardless of whether or not you think moisture is or will be a problem. The fact that foam is over the OSB tells me that there may have been a high level of moisture trapped behind the foam at some point in time. OSB will expand with high relative humidity alone.

Whoever mentioned the strength axis has a great point too. Even CDX plywood will buckle between the studs if ran vertically, under certain circumstances. The strength axis with OSB has to run perpendicular to the studs for best performance.

I'm also not fond of 2' centers with 7/16 OSB under any conditions. I know it's span rated, but I still have my doubts as to how it will perform under that condition.

The bottom line is too many factors are working against you here and unless you gapped the sheets, none are in your favor, regardless of how it's fastened.:thumbsup:


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## loneframer (Feb 13, 2009)

RMcBride said:


> We checked everywhere -* it was installed during our dry months* - covered with the foam the day after it was hung. No sign of moisture on the outside or inside. Insulation is bone dry as is the drywall.


 This may work against you, due to the fact that the material will expand with high humidity in the air.


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## Joasis (Mar 28, 2006)

I hate to be the first one to predict what is coming, but you will be re-sheathing the house where the problem is. Where it is still straight on the house, it probably is fine. 

Dry sheets + butted tight = bowing between studs when humidity is high. 24 centers didn't help, but would not have mattered with proper spacing.


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## festerized (May 19, 2007)

Could there be a chemical reaction with the glue from the OSB and the foam?


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## Cletus (Jan 7, 2008)

RMcBride said:


> ...is bowing out from the house between studs a good 4-5 inches...
> 
> Any thoughts?


Across a two foot stud bay, the material would have to expand at least an 1 1/4" (5%) in order to bow out by 4". A 1/8" panel gap would be irrelevant at that rate of expansion. I believe 1 or 2% is the typical rate due to changes in humidity. It was stated that there was no evidence of water intrusion found. If it's even possible, the panel would have to be soaking wet to begin to expand by 5%, and I would expect it be crumbly mess of wood chips at that point. 

I don't have the answer but I suspect gapping or stud spacing is not the problem here, and I can't believe moisture caused this without leaving evidence.


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## Framer53 (Feb 23, 2008)

Cletus said:


> Across a two foot stud bay, the material would have to expand at least an 1 1/4" (5%) in order to bow out by 4". A 1/8" panel gap would be irrelevant at that rate of expansion. I believe 1 or 2% is the typical rate due to changes in humidity. It was stated that there was no evidence of water intrusion found. If it's even possible, the panel would have to be soaking wet to begin to expand by 5%, and I would expect it be crumbly mess of wood chips at that point.
> 
> I don't have the answer but I suspect gapping or stud spacing is not the problem here, and I can't believe moisture caused this without leaving evidence.


I am with you Cletus!


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## MattK (Apr 2, 2009)

Have you called your supplier and/or manufacturer to see if this is a problem others have seen or if youre the only one. Im sure this batch of sheets they made thousands, maybe tens of thousands so some of them followed you to KY. See if other guys are experiencing this problem.


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## festerized (May 19, 2007)

http://www.sunsationalgreen.com/?p=694
. Polyurethane serves not only as the insulation and sealant, but it is also the bonding agent / self-adhesive that bonds to the OSB. Gorilla Glue, which is touted as the strongest glue in the world, is made of polyurethane. It does not delaminate. He might have heard about expanded polystyrene (EPS) SIPs, which didi have a history of delamination due to the glue aging. In the case of EPS, it is not injection molded like polyurethane is. It is cut into blocks or slabs and then glued to OSB. Previous generations of glue caused delamination when aged. I think that problem has been resolved. But it has never been an issue with polyurethane SIPs, which have been used since 1938. Even stainless-steel, galvanized-steel, and aluminum skins adhere to the polyurethane core. Walk-in cooler and refrigeration panels have been made this way for over 60 years. The ICC adopted polyurethane SIPs into the IRC in 2009.


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## Tom Struble (Mar 2, 2007)

we had an issue like this with the osb bowing between studs on a stucco house if anyone remembers


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## Leo G (May 12, 2005)

Foam acts like a vapor barrier. Does the insulation have a vapor barrier on it also? You may have trapped the OSB between vapor barriers. Did you check the OSB with a meter or with a touch by your hand? 24" OC and a 5" buckle sound extreme.


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## KennMacMoragh (Sep 16, 2008)

I've only seen anything like that happen once. It was due to slamming the sheets tight, no gap, then it got rained on before the siding went on. Siding was torn off, then I remember someone trying to fix it by cutting a relief joint between every sheet. That didn't work, we ended up having to tear off the OSB and re-sheet it, which is what you will probably end up doing. 

Who ever didn't gap the sheets should be the one tearing off the OSB and re-sheeting it. He will learn not to do that again.


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## Leo G (May 12, 2005)

What I don't understand about sheet gapping is the sheet goods come in at 48 x 96. If they wanted gapping they should come in at 47 7/8 x 95 7/8. Otherwise adding an 1/8 gap is going to throw your 16/24 OC off. Or do they expect you to cut every sheet?


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## JonM (Nov 1, 2007)

Leo G said:


> What I don't understand about sheet gapping is the sheet goods come in at 48 x 96. If they wanted gapping they should come in at 47 7/8 x 95 7/8. Otherwise adding an 1/8 gap is going to throw your 16/24 OC off. Or do they expect you to cut every sheet?



Stop trying to make trouble Leo...:laughing:


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## Leo G (May 12, 2005)

Whaaaaaat ?!!!? It's the manufacturers with there rules and not providing the proper sizes to accomplish said gapping. How do they expect people to follow the rules? Another thing is by butting the sheet goods together you make a strong house, leaving a small gap there encourages racking and wind shear movement. This makes the nails the primary source of racking resistance. If you push a nail back and forth for any amount of time it will come loose..

Just a trouble maker am I.


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## JT Wood (Dec 17, 2007)

We always sheath a house horizontally.

leave 1/8" gap at the top and bottom
butt the sides tight.

leo's right though, I'm not gonna start Framing my house @16 1/8" centers

I've personally never had a problem, With butting tight.

I have seem problems when there is no gap at the top and bottom.


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## loneframer (Feb 13, 2009)

There are several ways to deal with end gapping.
If using conventional 2x material, I always cheat the sheet off center to allow for some spacing. On long runs, you may have to cut a sheet or two. With wide flanges, such as I joists, no cutting is required.

Less popular in my book, is running the sheets butted tight, then curfing the seems after. This creates two issues. One is destroying the sealed edge of the sheet, the other is added time.

Also, as Hughjazz mentioned, There is the option of adding 1/8" every 8", which isn't a big deal if you get in the habit of it. During layout, pull 15 1/4 and so on, up to 79 1/4, then 96 3/8.......................192 1/2..............287 5/8. If you already plan for spacing, this becomes as second nature as making sure the proper nails are in the gun.


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## Tom Struble (Mar 2, 2007)

http://www.buildingscience.com/documents/insights/bsi-038-mind-the-gap-eh

this was posted at jlc....interesting osb foam relation ship


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