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OSB Use

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Stress02

Structural
Feb 6, 2004
90
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.
 
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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.
 
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.

 
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?

 
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?
 
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?
 
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 for additional inspection tips.

What is the code body you are working in?
 
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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