I don't understand T&G sheathing......

Started by MushCreek, July 15, 2011, 06:21:19 PM

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MushCreek

....plywood, specifically. As long as I've been alive, most building materials are based around 48" wide sheets, or things that divide evenly into it- 12", 16", 24". Along comes T&G sheathing, and it only measures 47-1/2". How are you suppose to compensate for that? Make your building a little smaller, and space joists on 15.8125" centers? I went to a lot of trouble to try to work with standard sheet goods, and now I don't know what to do about floor sheathing. Seems like T&G is a good idea, but......
Jay

I'm not poor- I'm financially underpowered.

MountainDon

The sheets are placed with the 47 1/2" panel ends parallel to the joists, and nailed to the joists; the long dimension is perpendicular to the joists. The long side T&G joints fit together, basically unsupported except for the 1 1/2" where it crosses a joist. The T&G locks those unsupported edges together and makes the floor stronger with less flex at those joints. The length works out if the joists are placed properly.

The fact that each sheet only covers 47 1/2" can mess with covering the floor width as the half inch does accumulate across the width. Depending on the building width it can be only a couple inches or more. That was the reason I made my cabin a little less than the full 16 foot width. A narrow strip can be filled in on the final side and usually gets hidden under the bottom wall plate.

IMO, no matter how careful the planning is to make minimal waste of products somewhere along the line it doesn't work out. That's why I never worry about trying to use multiples of 4 feet.
Just because something has been done and has not failed, doesn't mean it is good design.


archimedes

You should be running the plywood perpendicular to the joists.  Therefore it wouldn't make a difference.

Oops.  Don beat me to it.
Give me a place to stand and a lever long enough,  and I will move the world.

firefox

Correct, but does anyone know why they are 47 1/2" wide?
Bruce
Bruce & Robbie
MVPA 23824

MushCreek

I see now how they're installed; it still annoys me to have a 24' design and either have to make it 3" narrower, or wind up needing a 3" strip. It's like all the recipes out there that call for a 12 oz. can of something, and the cans are all 11 oz. now.

As for why they are 47-1/2"- That's because they are all tooled up to make 48" sheets, but once the tongue is cut, you lose 1/2" in the new usable width. The sheet still is 48", but when the tongue fits in the adjacent groove, 1/2" is lost. It would probably take a major re-tooling to make a 48-1/2" sheet.
Jay

I'm not poor- I'm financially underpowered.


Don_P

That little strip is trouble as well. If there is going to be a ledger attached deck you really want the sheathing to be well attached to the floor joists and the rim... in that case rip the first sheet down so that the last sheet is a wider strip.

sako

You also have an option to get ff t&g that has a full 48'' face, most places have both.

Don_P

I recieved an email from PEte going into more detail on what I mentioned above;
QuoteYou might add to your last post, something like this...

Good shear diaphragm action of a floor, roof or wall diaphragm depends on fairly full sheets at the edges of the diaphragm to prevent racking or provide the shear action back into the diaphragm. That is, good nailing, and tighter nail spacing, btwn. the rim jst. or the edge jst. and adjacent jsts. across a full sheet of sheathing. The full sheet is a very effective shear panel, while a narrow piece of the same material suffers from the same weak shear joint as shiplap sheathing suffers from; it allows slip at this joint instead of transferring shear across the joint. This nailing may be the primary lateral load connection btwn. the floor diaphragm and a ledger or rim jst. End nailing and toenailing btwn. jsts. certainly isn't. Diagonal shiplap sheathing provided some diaphragm action by virtue of a truss type diagonal action w.r.t. the jsts. While shiplap perpendicular to the jsts. did not provide much diaphragm action, except that the many joints with the jsts. and each piece of shiplap, and two nails at each joint developed some moment btwn. the nails in that joint, and thus resisted some racking. Plywood or OSB sheathing is a far superior material for resisting the shear we are dealing with. Thus, it is not a good idea to use a narrow strip, 8' long, or a 4' wide piece spanning only one jst. space, at any edge of a diaphragm.


diyfrank

The T&G osb floor sheating I used messured 48 + the tongue 1/2 inch. I'm not sure of the brand but some was gold edge and some I'm not sure. On my 16' wide floor I had trimmed a full inch off. I'm thinking it comes manufactured both ways.
Home is where you make it


MushCreek

Well, you'll never learn much from the manufacturer's websites! Advantech calls theirs a '4 X 8' panel, but in the fine print, it does mention '47-1/2" net width'. The Edge Gold had no information, other than to say it comes in 'standard sizing'. I did find a thread on a forum somewhere that said the Edge Gold is in fact net 48". I guess once I find a dealer, I'll have to measure the stuff. I know the stuff they carry in the big box stores is 47-1/2". I could split the difference, and have a strip a few inches wider than 24" on each side, but then I waste X amount of sheets by ripping the stuff. I'm not sure where else I would use it, and it ain't cheap. I could also re-design my house to correct the spacing, but that idea really gripes me.
Jay

I'm not poor- I'm financially underpowered.

Don_P

I generally find places to use excess osb and ply. Stair treads & risers, mech chases, closet sides, etc.
I've only run into full dimension once and cannot recall where that was.

Troyy108

Quote from: MushCreek on July 15, 2011, 06:21:19 PM....plywood, specifically. As long as I've been alive, most building materials are based around 48" wide sheets, or things that divide evenly into it- 12", 16", 24". Along comes T&G sheathing, and it only measures 47-1/2". How are you suppose to compensate for that? Make your building a little smaller, and space joists on 15.8125" centers? I went to a lot of trouble to try to work with standard sheet goods, and now I don't know what to do about floor sheathing. Seems like T&G is a good idea, but......
For real bro I framed my platform exactly 12'x16' with 2x8 joists running the 16'. Put a drop beam in the middle to support it. Reason being I had a bunch of extra 2x8x16s and am building a shed with them. Then went and picked up the T&G subfloor running it perpendicular to my joists. So it was an 8' piece followed by a 4' piece then staggered it on the next run. My frame was exactly 16' I carefully planned that but I get to the end and I'm 2" short. I saw some extremely rude comments on some other sites saying we should've planned for this instead of blaming the material. **** that I say! How about mill some damn plywood to 48½" so when they cut the tongue and groove, the piece ends up 48" wide! I actually called my very experienced framer buddy and he said he never realized it was like that. Stupid if you ask me. I guess they just always cut their plywood 4x8  no matter whether they make it T&G or not