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Quality before quantity
122 Posts
What is OSB?
To be fair to Knucklehead,I know in Canada OSB is called Aspenite,although I think it's actually a brand name.
Ask for OSB at a lumber yard up there will usually get you some weird looks.
Found that out fixing a friends cottage.

Couple other different names for the same stuff:
ardox nails =spiral nails

Rory Read
29 Posts
Plywood is more permeable than OSB

I just finished framing, sheathing and siding a new build for a client here in Portland, Or, who was very focused on getting the very best wall assembly he could afford. Houses fail in Portland because of rain, mold and eventual rot (and every 400 years or so the ground moves around a bit). We tried very hard to build the best wall we could for his budget.

Plywood is slightly more permeable (breathable) than OSB, so water vapor will more readily pass through it.

I try to stay clear of OSB because I see it swell. I assume the water is penetrating primarily at untreated cut edges. Plywood will also delaminate eventually, but it does it doesn't seem to expand endlessly. Tile and roofing installer universally have the same preference.

He decided that the plywood was worth the added cost, and I agreed with him. I don't have the numbers right in front of me, but I believe it added about $400 to a $17k framing, sheathing & siding pack.

The website of the Building and Construction Technology School at UMass Amherst has an article by Paul Fisette called "Choosing Between Oriented Strandboard and Plywood."

The DOE Building America web site has a BSC article titled
Insulations, Sheathings and Vapor Diffusion Retarders.

I think that if I were building in a dryer climate or building a non breathable wall, I would go with OSB instead.

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