We have been encouraging builders to follow the ENERGY STAR recommendations to go with advanced framing methods. For this discussion I'm referring to 24" oc studs.  Many have gone with it & not had any problems.  However, a couple have had some considerably bowed sheathing (OSB)  & first suspect was that they are not gapping it as required.   They claim they are getting the 1/8" gap.  We are in the Pacific NW and it does stay wet a lot here but the builders take reasonable precautions to avoid excess exposure.... 

Not sure where to go from here... I think we'll try to meet a representative of the OSB manufacturer on site and get their opinion.  Has anyone else had this problem? 

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One reason could be too much moisture in the lumber when framed, and as it dries, wet lumber can twist and bow. 2x6 finger jointed studs and plywood is better framing material, especially in the Pacific NW.

IMHO & as a builder - OVE is the worst idea to come down the pike for most areas.

Armando does make some good points but I am leaning more towards a moisture, quality, &/or thickness issue. While a board might be rated for 24" OC, that doesn't mean it can handle it if it gets slightly damp, etc...1/2" is the minimum I would consider if not 5/8 T&G (preferabbly one rated for moisture)

 

Thanks Sean!  The acronym OVE is similar to OSB?

Sorry - OVE is Optimized Value Engineering i.e. 24" OC walls or as some like to call it (so it sounds better) Advanced Framing

On the plus side, Ladders & 3 stud corners are great - as for the rest one should really think about the pros & cons before jumping in

Now if you were meaning it as OVE being as bad as OSB, I would disagree because there are plenty of great OSB products out there (just like there are a few good OVE techniques). The catch is quite a few builders choose the cheapest & thinest products they can use. While these products maybe able to handle everything in a perfect environment, I have yet to see a job site ever come close to being perfect

I doubt the framers are gapping the material, ive had them tell me they are and when i get to the job, they are not, another reason might be the framers are not crowning the studs, while all of us old framers did it alot the the new construction is blow and go and they are not crowning the studs. Still being the the NW, I assuming west of the cascades? plywood would be a much better solution for a number of reasons, still need to gap the material, but such a much better material long term without alot of cost differnece in many casses. 24 inches on center is not a new technology for this area, Super good cents homes started this in the early 90's in Oregon, and Washington with thousands of homes with no problems. My bet is they are not gapping the material, i physically had to oversee this when starting some framers on homes, and after they tore off their sheating a couple times they realized we were serious, the problem went away. good luck.

The best suggestion we have is to gap the OSB a bit more... 3/16" especially when we know it's going to get wet much which is nearly all the time here.  Tad has probably called it right about the framers not really even gapping it the 1/8"...  The studs seemed to be crowned the same though.  Agree too that we may have to ride herd on the framers for awhile until they realize they are getting called on it.

 

During the housing boom there were some cases in the midwest where OSB products were installed prematurely and not fully cured due to increased demand. Caused quite a few large issues for large builders. Not sure how your market is going up there but if it's anything like the rest of the country you can rule out this possibility!

Sounds like you're doing the best route: meet with the manufacturer and inspect the job sites to get to the bottom of it.

There's plenty of things that could go wrong... Improper storage times and conditions at the manufacturer, warehouse, or job sites. Using the wrong exposure grade. Improper installation. And check the designs, it may be an issue of poor moisture management in the wall design (most likely drainage plane issues).

Dr George Tsongas from Portland State U did some fantastic studies on a similar problem back a decade or so. I would think a call to that resource may enlighten your study of moisture issues in exterior wall component parts in the Pacific Northwest.

Jumping in late to this discussion, but I agree with Armando that 1/2" CDX is a far better sheathing material than OSB, which is typically only 7/16".

I've been building on 24" centers for 20 years and will use only CDX or 1" board sheathing. 

OSB is not only more vulnerable to deformation and swelling (primarily at edges which won't return to original thickness), but far more prone to mold and rot.

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