Plywood Vs OSB

 
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Old 02-16-2007, 11:14 AM   #1
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Plywood Vs OSB


Do you use CDX plywood or OSB board?

Besides price, what rationale do you use to justify one over the other.

Do you use any product comparison documentation to differentiate between the two options?

Where do you get your sources from if it is technical studies?

ED
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Old 02-16-2007, 03:11 PM   #2
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Re: Plywood Vs OSB


Plywood of course. OSB is real crap.

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Old 02-16-2007, 03:36 PM   #3
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Re: Plywood Vs OSB


I noticed after I posted this topic that the varying opinions were discussed pretty thoroughly in September and October, 2005.

Have there been any additional technical studies since then that truly correlate which one is better and for what purposes you should choose one over the other.

I ssudied up on this about one year ago, and if I can find the articles I downloaded at the time, I will repost them in this forum.

Hope this topic isn't too much of a dead horse looking for another beating.

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Old 02-16-2007, 03:54 PM   #4
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Re: Plywood Vs OSB


I'm a firm believer in osb. Though with substantial weather it will start to flake off, the structural integrity will not be impaired. Plywood, even cdx, will delaminate and loose its structural integrity with water.

Plywood has structural strength in only one direction, osb in two.
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Old 02-16-2007, 04:33 PM   #5
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Re: Plywood Vs OSB


We used to use plywood but have been useing 5/8 osb for years now and would nver go back.Have had several roofs where plywood delaminated and left little humps in the roof, never had 1 problem with osb.Sure plywood is stronger but osb is strong enough if you use 5/8.For the price differance its crazy to use ply.I wouldn't if it was the same price!
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Old 02-16-2007, 04:47 PM   #6
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Re: Plywood Vs OSB


But it takes a gajillion times the water to delam the plywood as it does to flake the osb, it seems.
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Old 02-16-2007, 08:28 PM   #7
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Re: Plywood Vs OSB


I have seen it time and time again with OSB sagging,delamination and just generally not holding up well at all, compared to plywood it is night and day
Its really just about price with the OSB fans.

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Old 02-16-2007, 09:14 PM   #8
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Re: Plywood Vs OSB


A while back I read a technical article by an engineered wood product manufacturer who made both products. The article was on plywood versus OSB Versatility, Stiffness, Creep - edge swell.

Here are the highlights to support my utilization of CDX instead of OSB.

OSB swell is generally greater than in plywood due to the release of compaction stress in OSB created during the pressing of wood chips into an OSB panel. Plywood that has swollen will return to its nominal thickness as the wood dries. OSB will remain swollen to some degree after it dries because the panel will still have the higher "compaction ratio" that was present as of the date of manufacture.

The comparison below, undertook by the APA, lists the thickness swell (in percent) using a water soak test.
Plywood Average swell= 6% to 8% depending on thickness
OSB Average swell= 10% to 15% depending on thickness

Over a period of time, when subjected to high humidity or a series of dramatic wetting events, OSB is more prone to panel swell than plywood especially at the edges. Panel swell is most noticeable along the edges where it is critical for flooring and roof sheathing to match-up as not to show through the flooring or roofing materials.

Research done by the USDA Forest Products Laboratory (Research Paper FLP-RP-574) shows that over an extended period of time, under low constant loads and temperature, and in high-humid conditions, OSB will sag or "creep" more than plywood.


50% RH Fractional creep values
1.4mm Plywood
1.7mm OSB

85% RH Fractional creep values
1.9mm Plywood
5.2mm OSB

Cyclic RH 50%-85% creep values
2.0mm Plywood
4.6mm OSB


Long-term, plywood sags less than OSB in humid conditions. In humid areas with vented attics and crawl spaces, using plywood for roof and floor sheathing can reduce risk of sagging roofs and floors.

APA Technical Note N375B states that plywood panel bending stiffness is 10% greater than OSB at equal joist spacing. Panel bending stiffness is the capacity to resist deflection.

Density of plywood is 34-36 pounds per cubic foot compared to OSB at 38-42 pounds per cubic foot.
One 23/32" 4'x 8' plywood piece would weigh approximately 67 lbs.
One 23/32" 4'x 8' OSB piece would weigh approximately 78 lbs.

Plywood is approximately 15% to 19% lighter than OSB. While the additional weight of OSB does not mean increased strength, it just means that it is heavier to handle on the job. In addition, OSB's higher weight means higher thermal conductivity (thus slightly less R value) than plywood.

Plywood and OSB: Screw withdrawal or holding ability.

Group 1 plywood, made from the strongest species of wood such as Southern Yellow Pine, holds screws better than OSB.

Plywood and OSB: Nail withdrawal or holding ability.

As shown in APA report T2001-3A, plywood generally has higher nail withdrawal values using plain-shank, ring-shank, and screw-shank nails, even though OSB has a higher density than plywood. The numbers below reflect dry test conditions. The numbers vary some when tested under dry to wet-redry conditions.
Withdrawal strength (lbs/in. penetration)

Plain Ring Screw

5/8" Plywood
Mean: 79.7 316.3 83.7


23/32" OSB
Mean: 67.6 281.5 63.9

Nail withdrawal strength measures the force to pull the embedded nail from the nailed parts.

After roof sheathing or sub floor panels are nailed to the framing, nails will remain in place better in plywood than OSB.

Under severe weather testing, plywood is shown to be more impact resistant than OSB. Plywood outperforms OSB in the South Florida Building Code (Dade and Broward Counties) mandated use of the "large missile" impact test for materials used in walls and roofs.

Plywood is more impact resistant than OSB. This provides resistance to flying objects in high wind situations. More impact resistance provides added durability against accidents caused by impact on floors, roofs, and walls on the inside and outside of the home.

Check out this link for more information.


http://www.sbebuilders.com/framing/plywood-osb.php

The previous link include links to 6 very comprehensive articles relating to the comparisons of plywood versus osb, both pro and con for either side of the fence. Use which ever endorsing information suits your purpose.

Ed

Last edited by Ed the Roofer; 02-16-2007 at 11:57 PM.
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Old 02-17-2007, 12:34 AM   #9
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Re: Plywood Vs OSB


I think plywood's considerable better. Strength and water resistance. The onle apparent advantages to OSB are the price, and the sad problem of the newer "young" plywood... The young trees and being peeled too small leaves a sheet that curles when it gets wet. Try sheeting a house with a stack of potato chips...not fun!
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Old 02-17-2007, 12:31 PM   #10
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Re: Plywood Vs OSB


While I would never argue the fact that ply is stronger we have had several cases where the sub floor got wet before under roof and the ply warped up and down between the joists and stayed that way even when dry, what a mess! Since starting to use osb about 10 years ago,it has never been a problem.
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Old 02-28-2007, 05:32 PM   #11
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Re: Plywood Vs OSB


Does it matter about water resistance? If roofed correct it won't get wet will it
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Old 02-28-2007, 06:41 PM   #12
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Re: Plywood Vs OSB


Yes it does, for several reasons. Once installed, depending on the interior attic and home Relative Humidity factor and the proper balance ventilation to expell this moisture, the product quite possibly could be affected resulting in negative consequences.

Secondly, according to the APA, per a document supplied to me via Certainteed, when OSB is delivered to the job site, it is in its driest state. Each and every sheet in the stack of OSB MUST be seperated by a minimum of 1/2" air gap to absorb the external ambient humidity for either 24 -48 hours. I forget the phraseology exactly, but that was the ludicrousness of the specifications prior to being capable of being installed properly to minimize the negative affects of the swelling that will invariably occur.

That would never happen in the real world!

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Old 02-28-2007, 06:56 PM   #13
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Re: Plywood Vs OSB


I'm not using any kind of particle board until they start bonding it with epoxies AND requiring that all cuts be sealed.

If you need to save a few bucks to build a home, do it somewhere where it is easily replaceable. Not in the structural components.
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Old 02-28-2007, 07:08 PM   #14
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Re: Plywood Vs OSB


Teetor,

You should check out the link I provided in post # 8, as it provides 6 well written articles, each positioning the values of one over the other. The most unbiased article IMO, is the one from GP, which at the time of writing the article manufactured and sold both products, which would tend to make me believe their arguments prior to one of any OSB organozation.

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Old 03-01-2007, 06:15 PM   #15
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Re: Plywood Vs OSB


Hands down CDX all of the time for roofing.

This has been discussed 100 times.

Not a scientific study BUT I have noticed on the roofs sheathed with OSB, tend to have much much more wood needing replaced when the roof gets torn off. Did two at the end of last year that were total resheats, built with OSB.

OSB is cheaper, if you want to build cheap go osb. It WILL certainly work in the short run.
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Old 03-03-2007, 10:00 AM   #16
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Re: Plywood Vs OSB


Don't listen to the guys from Illinois. They put iceshield on upside down.

OSB is stronger and can take on more water than plywood. Not sure how many times this has been proven. Plywood was used in the past, now it is only for under wood floors.

I don't see a 50 yr. plywood subfloor. There is one made of OSB and it is the strongest and most water resistant floor made.

Yes, this has been discussed and I will get pictures (I'm the only one who does) and show how good your plywood is.


Then Ed can rewrite this whole forum and put it in his book.
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Old 03-03-2007, 10:21 AM   #17
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Re: Plywood Vs OSB


We put our ice barriers on upside down? Sticky side up? I didnt know that...

OSB has one and only one advantage for cheapskates...its cheap. HArder to sell a pricier product, but some of us really can. LMAO
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Old 03-03-2007, 01:01 PM   #18
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Re: Plywood Vs OSB


Quote:
Originally Posted by MJW View Post
Don't listen to the guys from Illinois. They put iceshield on upside down.

OSB is stronger and can take on more water than plywood. Not sure how many times this has been proven. Plywood was used in the past, now it is only for under wood floors.

I don't see a 50 yr. plywood subfloor. There is one made of OSB and it is the strongest and most water resistant floor made.

Yes, this has been discussed and I will get pictures (I'm the only one who does) and show how good your plywood is.


Then Ed can rewrite this whole forum and put it in his book.
Comparing floors to roofs. One is interior and one exterior. I don't know how that matters.
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Old 03-03-2007, 01:06 PM   #19
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Re: Plywood Vs OSB


Sorry, I did not explain, I thought everyone knew about the flooring. It is a 50 year OSB product that is made specifically to take on lots of rain before the house is roofed. It is used on the higher end large homes.
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Old 03-03-2007, 01:16 PM   #20
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Re: Plywood Vs OSB


I just consider the source when someone clangs the bell of an obviously documented inferior product. The ONLY reason to use osb is to cheapen your costs for materials. Therefor, one who would do so, does not really care about furthering their craft, only in lining their own pockets as quickly as possible.

Someone who would sacrifice the entire quality of a 30 to 50 year roof by using a product that swells excessively and is made by gluing scrap particles of waste by product together, obviously does not care enough to study thoroughly enough to provide the proper products for their customers.

He obviously did not take the time to read the 6 technical articles I linked to, regarding the pros and cons of each product. The most unbiased report was from Georgia Pacific, which was manufacturing and making a profit on both products. It stated clearly and unequivically, that the plywood products had proven better in every category studied.

If 4-ply 1/2" cdx and 15/32 osb were priced exactly the same, would the osb rack ever sell out? (Maybe only in one place in Minnesota)

Ed

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