Subscribe or Renew Membership Subscribe Renew

plywood cdx -vs- OSB

newbuilder's picture

Seems to me this MUST have been 'talked about' here an there... but in addition to my general quiry I've got some very specific questions.  In general, I'm wondering what the upside of using plywood is over OSB as sub-siding.  I'm figuring there must be some advantage as I occassionally see builders using it despite it's costing a third again as much.

Also ... as to OSB 3/4 t&g sub-flooring ... any reason to go with plywood there?  Here in the PNW the OSB runs about $20 a sheet -vs- $30 a sheet for sturdifloor.

Lastly, any thoughts or wisdom on the relative WEIGHT  and the relative STRENGTH of 1/2" OSB to Ply?   I'm going to be working alone on a very high, narrow addition and these factors will matter.

Any feedback much appreciated - - Thanks!





(post #96549, reply #1 of 22)

Ah, but does plywood cost more than OSB? Today it might, next week it might be cheaper. Lumber and sheet goods prices are super volatile, especially in middle of summer building season. I live in BC and we could see the effects of the Florida hurricanes in our materials pricing on the opposite corner of the continent. Lumber yard I deal with was releasing as many as three contractor price lists a week because the prices were fluctuating so much.



Lignum est bonum.

Buccaneer Contracting

Penticton, BC

(post #96549, reply #2 of 22)

Yes ... but my questions are:

How is plywood better than OSB for sub-walls/floors?  Or isn't it? (If not .. why do some still use it though it clearly and consistently costs more?)

Does anyone know anything regarding the relative WEIGHT of ply to osb and of the relative STRENGTH?

And while I'm at it:  I'm going to be working alone in the rain ... hard to totally protect supplies ... is OSB more sensitive to moisture than ply?  Is there 'danger' in it's getting wet? 


Thanks again,



(post #96549, reply #3 of 22)

How is plywood better for sub walls or sub floors?.....Other than the fact that plywood tends not to delaminate as quickly as OSB  due to wet weather or swell as much in wet weather, the structural differences between the 2 are negligible.

Why do some still use plywood?....Personal preferences...also, availability is key; in that OSB supply at lumber yard may be low and "on order but not in stock", whereas the plywood may be in stock. Plywood is a tad lighter,...again, mostly personal preferences.

Relative weight and strength of OSB vs Plywood?... That has been answered before in many past posts on Breaktime...but the short answer is...basically, OSB is as strong as plywood....but that's assuming that both species are "high and dry" when installed.  OSB is slightly more heavier than ply, and when wet, if it stays wet for a long time, it will become weaker in that region that was exposed to the water.

But in normal situations, OSB holds nails and screws just about as well as plywood. And because OSB is heavier and stiffer than ply, it usually is more flat than plywood that's been stacked a while. Ply tends to bow, OSB tends to stay flat and least that's what I tend to notice when buying at my local lumber yard.

Is OSB more sensitive to moisture than ply?....Absolutely. Morning dew is not a big factor, but actual rain is a big factor. The more OSB is exposed to rainwater, the more it swells compared to plywood; and the weaker it will become over time if still exposed to rain water. Ply takes more water abuse.

Now here is one  for you...Have you heard of Advantech? It looks like OSB, but is totally 100% waterproof. It is tuff, durable, strong, also heavy, but will stand up well as a subfloor ( use T&G for flooring) or for wall sheathing, or for roof sheathing. Cost is very favorable to plywood and OSB...soooooooo...check it out !


(post #96549, reply #4 of 22)


One other thing that may be worth mentioning...CDX plywood is very "low grade" in that it is simply sheathing grade...has lots of large knots ( patches)  etc...and these areas tend to cause the sheet as a whole to seem a bit weak.

On the other hand, OSB is the same cosistency throughout the entire sheet. Also, plywood is never as thick as you order, it's a 32nd  or more undersized...whereas OSB is exactly on the money in the thickness department. A sheet of 5/8 OSB is exactly 5/8 thick but 5/8 plywood is only 19/32. And 3 ply plywood is definately not as good as 4 ply...there are differences...also if buying ply, make sure it is rated for exterior exposure. I may be wrong but I think all OSB is  rated for exterior applications regardless.


But as earlier check out Advantech products before making final decision.


(post #96549, reply #5 of 22)


thanks for the reply/info.

I tried 'googling' Advantech and it led me to multiple sites related to PC automation solutions!  Could you give me any further clues to finding what you're actually refering to?

Thanks again for the great reply!



(post #96549, reply #6 of 22)

(post #96549, reply #14 of 22)

Looks like the "Huber engineered wood products" are out of the question for me anyway ... a moot point.  If their 'dealer locator' is to be believed there is no one in my area that carries it ... not anywhere near Portland, Ore. or Seattle or Spokane Washington.  Guess the West Coast is, from some points east, still considered the boonies! 

Thanks for all the response.  I'll be checking the archives as well.

I'm embarking on a forty foot tower ... my 'vertical condo' ... 'house on end' ...with four rooms stacked one upon the other each only 14'X19' but with small extended decks on two sides.   The county has nearly ok'd it now .. although the engineers shook their heads a lot during intake.  It'll  stand a minimum of 10 feet above everything around it ... 360 degree view with a roof garden.  I'm a 'self-trained' builder who's only done a few pretty minor things ... but I'm figuring my next year or more will be pretty much about nothing but this.  I've got a budget that covers pretty much materials only ... so .. I'm doing everything but the foundation.  I'll try to share pictures as i get underway.  Probably be asking late night questions as I go as well. 

I'm nervous about this .. but excited.  My last 'big project' before I retire into a physically quieter life.  I hope.

Thanks again!




(post #96549, reply #7 of 22)

Terry, I would have to agree with Davo all the way.  The only thing I wish to add is that my experience has been that osb is slightly stronger than plywood of the same thickness.  That counts a lot on a roof.  It just does not seem to give as much when you walk on it.  I have heard of the new product he mentioned but have not seen it.

James Hart

(post #96549, reply #8 of 22)

You're kidding with that last statement, right?

(post #96549, reply #9 of 22)

Which statement?  If you  are refering to Advantech, I have not ever seen it.  Remember, this is Alabama.  We do not even have Oxy belts down here.  I am constantly learning of products that are being used elsewhere in the USA but not here.  Most of the time I read about it in magazines.  I lived in Portland , Oregon, for about 3 years in 1977 thru 1980 and when we moved back to Alabama I knew things about construction that no one knew here.  What can I say?  There are building techniques used by other framers in the country that are never done here.  Yes, we are a little behind concerning currently available building materials and techniques but I for one am wide open to learn.


(post #96549, reply #10 of 22)

Actually I was talking about when you said that OSB was a more rigid product on a roof compared to CDX.  I've never seen anyone put a boot through a roof sheathed in 1/2" CDX or better, but I've seen it happen several times on roofs sheathed in 1/2" OSB.   I also see more telegraphing of the rafters through roofs sheathed in OSB as opposed to CDX.   That's what I was getting at.   Not your fault if products aren't available in your area....wouldn't hold that against you.  Just didn't agree with your roof comparision.  I probably could have been more diplomatic about it than I was though, my apologies. 

(post #96549, reply #13 of 22)

The 1\2 inch cdx we have here is very weak.  I do not know how it is elsewhere.  The last time we used it for sheathing it bowed between studs 16 inch on center.  Had to tear it all off.  Georgia Pacific paid for the labor and materials.  It was a faulty product.  WE have never put a boot through osb or plywood but the osb does seem to be stronger when walked on.  At least that is the concensus of all my crew.  We have put down a lot of  the osb tongue and groove for sub floor.  It does swell up but we have had a lot of problems with regular sturdifloor delaminating after a rain.  I put the osb in my house 17 years ago and have not had a problem.

Can you tell me how to put pictures on one of my post?  I took the pictures yesterday and put them in a file on the computer  but have never put them on the web.  One of the other guys wanted to see this house we are working on.


(post #96549, reply #15 of 22)

When you are replying to a post just scroll down a bit in that screen... you will see an "attach files" button.  Click on that and then click "browse" to find the pics on your computer.  After you've selected a pic, just click upload and wait a minute or so.  Then you can repeat the steps from "browse" to add more pictures.  When you're done uploading, click "done" and it will take you back to your reply text.  Good luck, and sorry I don't agree with you regarding OSB's integrity.  To each his own, right? 

1. "reply"

2. "attach files"

3.  "browse"

4.  "upload"

5.  repeat from "browse" if necessary

6. "done"

7.  "post" as you normally would

(post #96549, reply #17 of 22)

You forgot 4B

"Wait for the file name to appear in the attachment box - sometimes a long wait"


 <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!



Oh Well,

We did the best we could...

(post #96549, reply #18 of 22)

Thanks for the info.  WE finally realized that Norton Security had the pop ups blocked.  When we selected *attach files* nothing would happen.  Any, we finally sent the pictures.  Thanks again.

James Hart

(post #96549, reply #16 of 22)

You should be able to find 5-ply doug fir CDX in 1/2" and 5/8"....pretty standard here in the PNW.

BTW, Dieselpig gave you the straight poop on posting pics, but when you hit "load", wait until you see the file come up in the upper part of the window before you hit "done."

Edited 11/6/2004 9:24 pm ET by Notchman


(post #96549, reply #19 of 22)

I did some surfing yesterday looking for plywood information.

Saw some interesting stuff at some mill and wholesaler sites, that reinforced my thoughts that the buyer had better be cautioned when specifying and buying this stuff.

CDX was called out as "with mill stamp" and "no stamp."  Some inventories were labeled "blows," and some others "delams."

As we all know, you can get 1/2" CDX in 5-ply and 3-ply.

I didn't do searches to see what is out there in OSB, but I am sure there are different spec levels, as well as off-spec grades.

Remember this if you buy your lumber verbally, whether you go to the yard and speak your needs, or phone them in.  You are in clear danger of getting sold off-spec goods if you buy this way.

That is why I use written purchase orders, and state clearly my spec for whatever it is I am buying.

Gene Davis, Davis Housewrights, Inc., Lake Placid, NY



(post #96549, reply #20 of 22)

Thanks again, everyone.

I do appreciate the feedback.  It will make a difference on how I move forward on this.



(post #96549, reply #21 of 22)

It's important to note that stiffness and strength are two different things.  OSB may bend less when you walk on it, but it might break under a lower load than plywood.  It seems to me that OSB fails more suddenly than plywood.  It snaps all at once instead of creaking and cracking a little as it starts to fail.


-- J.S.




-- J.S.


(post #96549, reply #22 of 22)

Very true.

If I need to make a hole in OSB for a crane strap, for instance, my 23 oz. claw hammer is unsheathed.

Ply either demands more speed and determination or a blade.


Jon Blakemore


Jon Blakemore

Fredericksburg, VA

(post #96549, reply #11 of 22)

Advantech is THER sjheathing material of choice

Costs are similar to plywood.

osb - Deiselpig already explained there.

If hand nailing, the ply is much easier on you than osb or advvatech because the wood is not as dense as the resin and binders in the other products.


 <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!



Oh Well,

We did the best we could...

(post #96549, reply #12 of 22)

BTW, you might try the seach button also. This has been discussed twice in this past month, more or less.


 <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

Welcome to the
Taunton University of
Knowledge FHB Campus at Breaktime.
 where ...
Excellence is its own reward!



Oh Well,

We did the best we could...