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OSB Use

OSB Use

(OP)
With the current state of affairs/pricing with plywood, I would appreciate any personal experiences using OSB as a substitute for commercial projects.

The only side effect that I have read about is that OSB has a sudden failure mode at the limit. I thought that might be less of a concern with a bit of overdesign.

One client claims that it is more stable with respect to delaminating and warpage than plywood, but that is just one opinion.

Any and all opinions will be appreciated.

RE: OSB Use

APA rated sheathing whether plywood or osb, should perform the same mechanically (bending, shear, etc.) if the APA rating is the same.  That being said, some contractors in my area prefer plywood for roof sheathing and have no preference for wall sheathing.  The few incidents of poor performing osb, that I have read about, have been attributed to improper installation (spacing between sheets).

RE: OSB Use

Only thing I heard about OSB is it tends to shatter more when edge nailing is very close.
As an engineer, it makes no difference to me whether OSB or plywood is used, as long as the material used is APA-rated properly.  

RE: OSB Use

Lots of problems with OSB....more to follow!

RE: OSB Use

Ron, I'm glad you said something.  Without having any supporting data or studies, I was afraid to chime in.

Our policy is NO OSB ALLOWED, no exceptions. My boss calls it "wood sponge board".   But we don't do new design, remediation only, primarily in the SF Bay area.  We also do failure analysis and litigation work.  We have plenty of anecdotal evidence that OSB does not stand up as well to high humidity and exposure to moisture.  It also seems to be a bit better at providing a growing medium and food source for mold. And the truth is, it is a rare project that building materials are handled exactly as the manufacturer states in their literature, which is usually substantially different from what the sales rep will tell you.

As far as cost, it's variable, but plywood generally runs about $3 more per sheet than OSB.

I'd love to know if there is reliable 3rd party test data comparing plywood and OSB under less than ideal conditions.  So far I've not run across it.

RE: OSB Use

Cass,
Your boss is confusing OSB with particle board. OSB isn't all that bad. As far as mold goes, I found it amusing that it is an issue. After all, every wood stud, joist, beam, and truss is mold food.  

RE: OSB Use


Nope, the boss may be over-reacting (he has a tendancy to do that), but he's not confused about the material.

Like I said, I have plenty of anecdotal evidence that does not cast OSB in a particularly good light.  For our particular projects and clientele, three bucks a sheet is no big deal.  But I would not go so far as to tell any of our contractors to voluntarily substitute plywood for OSB on a competatively bid project.

RE: OSB Use

I have done several failure investigations on the use of OSB, for roof sheathing and for wall sheathing.  It has good structural strength under dry conditions, but will deteriorate under wet conditions, and in a different failure mode than plywood.  OSB swells at the edges (I have measured the swelling from the edges completely across sheets in 1-inch increments, then plotted the results.  Looked like a parabola) and plywood plies start to ripple as they fail.

OSB will swell at its edges even with small amounts of moisture increase.  This happens primarily on roof sheathing.  The edges swell, the board increases in length and volume, and "picture framing" results.  You see waviness in shingle roofs from its dimensional instability.

If you subject OSB to the same testing done for plywood for durability (boil specimens in water), you get a significantly different result (OSB will sometimes fall apart..not always, but not predictable either).

The concept of OSB is great....the process used to keep it competitive with plywood makes it less durable and less predictable.

I have never heard of a class action suit involving plywood.  There are numerous class action suits involving OSB and OSB-like materials.

I won't specify it, even though it achieves APA span ratings and the like.

RE: OSB Use

Ron, plywood also expands (as in becomes 48.2" x 96.2")when wet and buckles when there wasn't enough joint space. Also, I have seen plenty of "ripple" on roofs, no matter what OSB or plywood.
If your drawings specify APA-rated shtg, you are legally not at fault. Lawyers retain unethical "expert" engineers, same as ambulance-chasing lawyers retain unethical "medical expert" doctors. They invent reasons for malfeasance, and OSB is just a handy victim. The judge doesn't know any better. Plywood has a nasty habit of delaminating when rained on before the roofing, and I have heard builders say that's why they prefer OSB for roofs, and plywood for heavily nailed shearwalls.

RE: OSB Use

FalsePrecision...I agree that specifying APA Rated Sheathing helps you comply with the standard of care and puts you on better legal footing.

Given leaking and saturation, both will deteriorate and in different modes.  In general, they are not rated for continuous wet service, only intermittent exposure.

I have tested both OSB and plywood.  While each has some specific advantages, in my opinion, plywood is the overall better choice.

RE: OSB Use

I agree with you Ron, both products are viable but in the long run plywood is the best choice.

Comparative product data on Plywood and OSB can be found at CanPly's website. There are engineering values for both plywood and osb on axial compression, planar shear, bending and tension and thickness swell.


JB

RE: OSB Use

(OP)
We chose to keep plywood the standard irregardless of the checkbook.

RE: OSB Use

Stress02....good move.

RE: OSB Use

Well we keep beating this to death...
Seeing as how a client may be a builder of large, repetitive apartment complexes, that are built in many different locations, I think it is "none of my business" to allow ONLY plywood. It is the builder's choice, as long as it is APA-rated. You might notice that manufacturers of OSB tout their product as being superior (grain of salt).

RE: OSB Use

You're right about that FalsePrecision...however here on the Wet Coast of British Columbia many builders have been forced to replace all of their rotting OSB with Plywood in the leaky condo crisis of the late 90's. Specification in the Code, Certified by APA or not doesn't always cover your butt!

RE: OSB Use

OK, jbpeng- your point is valid...I am in Arizona, and except for the last few months being pretty wet, it is obviously different weather here.

RE: OSB Use

Anybody have experience with enhanced OSB products like Advantec? I hear this is great product!

JB

RE: OSB Use

Two thoughts on this. First - At a seminar one time the maker of the Simpson Strongwall said that Simpson uses this product for their shearwalls because OSB is better in in plane shear. Second - I have never seen a Wood "I joist" with Plywood used for the web.

RE: OSB Use

triggerfish,

Although the trend of the I-Joist manufacturer today is to provide OSB webs, Trus Joist still have series of joists using Structural 1 Plywood webs.  In fact, traditionally, the webs were made with plywood and flanges using sawn lumber.  The industry has evolved over the years and now they have various combinations of OSB/plywood webs with LVL flanges.

RE: OSB Use

(OP)
As a consultant, it's my responsibility to provide my clients, who are the Architect and the building owner on any given project, with the best permanant solution without exposing myself to extra liability that arises outside my control.

With that in mine, if there is any question on a prodect's performance or durability, then it is not specified. Some say to merely specify "sheathing" and let the Contractor choose. In my opinion the designer is still liable because he did not prohibit the use of that specific material.

An example comes to mind; twenty years or so ago an Architect wanted to use "fire treated" lumber in prefabricated roof trusses. The industry was unaware of any issues at the time, so the building in mind, as well as several others, was built that way. About 5 or 6 years later the industry accepted and announced the fact that it was wrong to use that material because it was corrosive to the truss connector plates under certain conditions. The Architect, builder, lumber supplier and truss manufacturer all ended up in court. In hindsight, what was deemed alright due to lack of prior knowledge ended up causing many people bad times.

It seems that the OSB negatives outweigh the positives for me just by virtue that negatives exist.      

RE: OSB Use

My perspective, NOT as a professional (this isn't my area of expertise),  but as a PE who happens to do a lot of home improvements and relief projects (such as roofing replacements in Florida, recently).

In the areas I've worked, OSB is both allowed and more commonly used, primarily due to cost.  However, as one who walks on a roof occasionally, there's no doubt that the OSB has less strength than plywood of equal thickness.  

I know "H" clips are required when OSB is used,  but I'm not sure if "H" clips are required when plywood is used.

The difference, though, comes in when repairing or replacing roofing shingles.  The common methods of removing old and/or damaged shingles is "shingle spades".  These severely bend existing "H" clips, and no amount of hammering will completely straighten them out.  When the roofing felt is laid and nailed (very specific requirements have been recently implemented in Florida, BTW, as a result of last summer's storms), a hole is created everytime you step on the felt over a "H" clip.  

This seems like a case of very inconsistent, perhaps not well thought out code requirements.  If plywood was required, and/or perhaps closer joist spacing, then "H" clips wouldn't be required, and you'd have a tighter product if/when the roofing is replaced.

RE: OSB Use

Mshimko,

H-clips are required for panel edge supp)orts (OSB or Plywood).

In Canada, H-Clips should be spaced:

One at midpoint for supports upt to 600 mm
Two at 1/3 points for suports 601 to 1000 mm on centre
Three at 1/4 points for supprts more than 1000 mm on centre

I've heard about a Plywood T&G (Tongue and Groove) Profile for Roofs called EASY T&G that supposedly eliminates the need for H-Clips.


Does anybody have any experience with this product?

RE: OSB Use

Wondering if anyone has some advice. I am looking at purchasing a new home, recently constructed. My inspection revealed that the builder used 15/32" OSB for the roof decking and the truss is spaced 24" oc. He did not use H clips. I know that our local building code is that H clips are required for that spacing on decking that is less than 23/32" thick. Does anyone know of anything that can be done now to remedy the problem?

RE: OSB Use

I assume this answer isn't the one you're looking for:  if a house was built with obvious code violations,  DO NOT BUT THE HOUSE!   As to "repairs after the fact",  the only options I can think of is (a) remove the existing shingles, add another layer of OSB (with clips), and reshingle,  or (b) remove existing shingles AND sheathing, and re-apply properly.  "a" above is probably cheaper, but I'm not sure about the additional weight on the roof.  Another consideration is this:  what other code requirements did the builder not meet?????

Another question I would have is - who was the local inspector who failed to do his job?   

RE: OSB Use

Kory313, recommend considering adding solid blocking at the OSB seams, glueing the paneling to the 2x4 and nailing them to the trusses.  The blocking would eliminate the deflection issues and close off the diaphragm.  Check if the OSB panels were installed with proper spacing for expansion.  In practice the H clips act more as a spacer then a structural member.  Checking if the ridge vent is blocked and the proper nail size were used.   See http://www.eng-tips.com/viewthread.cfm?qid=83309&page=4 for additional inspection tips.

What is the code body you are working in?

RE: OSB Use

One note about OSB vs Plywood.  OSB has constant values thoughout its thickness.  If the exterior plies of plywood are punctured, the panel looses about 70% of its strength.

If you have ever watched a group of contractors with nail guns, you will see they get the gun bouncing off the deck.  This means that the gun is not calibrated correctly.  It also means that the fastener is puncturing the top ply and reducing the effective shear value of the panel by 70% (+/-).

This does not happen with OSB.  In addition, reports of failed fastener pullout in OSB were actually the result of stable fasteners awith only (1) leg engaged.  OSB actually has a better pull out strength that plywood.  

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