OSB or Plywood for Truss Gussets?

   / OSB or Plywood for Truss Gussets? #61  
The only reason you even see OSB is because it's cheaper and easier to work worth. Quality plywood is stronger in every way than OSB. Emphasis on quality. The multiple layers of crossing grains make it very strong in shear and compression.

Those notions are about 15-20 years behind the times. OSB has an even more isotropic distribution of crossing grains than plywood. Money has nothing to do with it -- many of the engineered lumber products are better because of the OSB construction.

There are cases where plywood is better, and cases where OSB is better. There is not a general conclusion to be made. You need to look at it on a product by product basis.
 
   / OSB or Plywood for Truss Gussets? #62  
The only reason you even see OSB is because it's cheaper and easier to work worth. Quality plywood is stronger in every way than OSB. Emphasis on quality. The multiple layers of crossing grains make it very strong in shear and compression.

And Quality plywood is not inexpensive or easy to come by. The last dozen sheets of 3/4 PT plywood I have bought over the last 4 years all required going thru three times as many sheets just to find ones where voids didn't line up.

I can't make my own plywood. At least I'm finally getting in position to make my own dimensional lumber. Last week I spent about 20 minutes trying to find 6 good PT 2x4's at HD, I went thru half a stack and only found 4. All the rest were "bark pieces". The guy in the checkout line in front of me had a stack of about 20 2x6x10' and bragged he found 1 piece without a big knot.
 
   / OSB or Plywood for Truss Gussets? #63  
OSB is superior to plywood in roof decking . It holds nails much better and it can be reroofed multiple times. Plywood splinters and delaminates when nailed. It's possible to get a second roofing on a plywood decking, but you would never want to do it a third time. From what I'm reading in the trade magazines, OSB is also better on sub flooring and on the exterior walls. For sub flooring, its considerably stiffer when compared to plywood tongue and groove. For sheer strength in the walls it's biggest advantage is being able to get it in 4x9 and 4x10 foot sheets. The ability to have a solid sheet from sill plate to top plates on your framing is HUGE!!!!

Eddie
 
   / OSB or Plywood for Truss Gussets? #64  
If you had to walk over a three foot gap and you could bridge it with 1/2 OSB or 1/2 plywood - which would you expect to hold you?
 
   / OSB or Plywood for Truss Gussets? #65  
I would recommend 1/2" plywood for the gussets (both sides of the 2x), and drive nails through and bend them over (clinch nailling). This is required for our building code.
 
   / OSB or Plywood for Truss Gussets? #66  
I just bought 6 sheets of PT 3/4" plywood from Lowes and 4 sheets of PT 1/2" (actually 15/32"). As usual the plywood was "damp". The 1/2" was 4 ply and TERRIBLE. It looked ok loading in the truck but I got it home and within 2 days, stored dry, 1 sheet partially delaminated down 1 side. After installing it and painting it 1 sheet has virtually delaminated, bubbling up where it soaked up the paint. The 3/4" is just slightly better.

I wouldn't recommend 1/2" commercial ply for anything stronger than a paper bag.

I have previously bought from the two local lumber stores and they sold the same quality in PT plywood.
 
   / OSB or Plywood for Truss Gussets? #67  
If you had to walk over a three foot gap and you could bridge it with 1/2 OSB or 1/2 plywood - which would you expect to hold you?

Why would anybody try to span 3 feet with either? Seems like a silly question. Even at two feet, I want to make sure the decking is on at least four rafters or trusses. If it was just a small piece two feet long, fastened at the edges, it will fail from it's own weight. When decking a roof, I will cut an 8 foot sheet down to six feet in order to get four feet on the next sheet instead of installing a two foot piece.

Eddie
 
   / OSB or Plywood for Truss Gussets? #68  
"..OSB has an even more isotropic distribution of crossing grains than plywood..."

Simply because it is composed of a multitude of tiny pieces. If someone is concerned about a few layers of veneer "delaminating" in plywood, then the same person should be having convulsions over the possibilities of all these tiny scraps of wood in OSB "delaminating."

OSB is used because it is usually cheaper. That's pretty much it.


As for failures in plywood, often that can be attributed to people not knowing just what they are buying.
For example, I still run across people who think CDX is "exterior." Which it is not.
 
   / OSB or Plywood for Truss Gussets? #69  
I think you guys are all missing the point of what the gusset does. It is there to keep the boards in the truss lined up and in position. In theory, the truss should work without a gusset or plate by fitting all the boards together that make up the truss nice and tight. The gusset is just there to keep them from moving around.

As mentioned by a few, the glue that holds them in place is what matters. Glue is stronger then the wood. The nails or screws are just there to hold the wood in place until the glue dries and makes it permanent. Half inch plywood is the norm and it's what I've always used, but in just about every other building use, I prefer OSB over plywood.

Eddie



This is correct. Look at a manufactured wood truss. All there is at the joints are 4x6 plates that have 1/4" teeth smashed into the wood at the joints. No glue! No way that will work!
 
   / OSB or Plywood for Truss Gussets? #70  
"...There is no load or weight bearing consideration on the gussets..."



Gussets provide the connections between those members.

No gusset, no connection. No connection, no truss.

They carry a load.

Properly constructed and braced trusses carry the load through the actual truss material from one properly mitered joint to to the next, to the bottom chord of the truss which then transfers the load to the rest of the structure frame. If the took the time to brace all of the truss members to reach other, you would not structurally need the gusset at all.

Like I say above, go look at a manufactured truss, you don't really think that 4x6 1/16th inch plate is carrying any load do you?
 

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