Plywood Direction Effect On Floor Bounce Over I-Joist - Framing - Contractor Talk

Plywood Direction Effect On Floor Bounce Over I-Joist

 
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Old 10-22-2007, 09:56 AM   #1
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Plywood Direction Effect On Floor Bounce Over I-Joist


The 9 1/2" ijoists I am using are rated for a 16' 8" span for L/480 deflection..

The house spans about 28 feet in width. In the back part of the house I ran the ijoists accross the house and there is a middle wall supporting the ijoist midspan.. That section of the house is fine as far as boucing.

However the front part of the house there is one room accross the whole 28' feet. This room is abot 14' deep. In this section of the house I ran my i josts front to back from the front of the house to a steel renforced LVL. This area bouces.. When looking at it from below it is not the beams that are bouncing but the ijoists itself.

I think this might be why, I started applying subfloor in the back of the house with the plwood going front to back (accross the joists).. However for the last 14' I continued running the plywood front to back (with the joists). In that area I have the bounce. Does running the plywood with the ijoists contribute to floor bounce? Everything is laid out correctly such that all my long plywood seams split the ijoists. Everything is glued and the crap was nailed out of it.

Is the direction of the plywood the major factor here?

I have three possible soltions
-Renforce both sides the I joist on both sides with rim board to make them stiffer. This is what is shown in GPs manual as a way to renforce cantilevers so should be helpful
-Add blocking at the mid point. I think this might be helpful as the ijoist seems to roll slightly as it starts to sag plus tieing them together will distribute the load somewhat.
-Add new i-joists in between these making the ijoists 8' on center at that point.
- Add filler block and anohter i joists (double them up).

Any recomendations? I dont like the idea of going 8" on center as that will make hard for highats.

Adding blocking is cheaper then renforcing but if I need to reinforce the ijoist after adding the blocking I will end up ripping the blocking back out. So maybe add the rim board to both sides of ijoists first and if that doesnt cut it I can then add blocking to that?

Was not changing my plywood direction when the joists changed direction my problem here?

gp manual is here(page 23 of 56 shows the method I was thinking)

http://www.gp.com/build/product.aspx?pid=1390
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Old 10-22-2007, 10:15 AM   #2
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Re: Plywood Direction Effect On Floor Bounce Over I-Joist


are you using tongue andgroove plywood and if i understand your layout how did ya staggar your pieces.inotherwords can i assume that each row of plywood rests on only four joists. the total span for these tgis are only 14' and they are secure to the sillplates and header?

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Old 10-22-2007, 11:08 AM   #3
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Re: Plywood Direction Effect On Floor Bounce Over I-Joist


Yes tongue and groove...

Standard stagger method, cut the first peice in 1/2 when starting the first row.

What I did before starting in the back was dropped a string line from the 4th joists and ran it all the way to the back. This way when the long edge of the plwood from the back reached the front it lined up with the front i joists.

yes.. each peice is resting on 4 joists in the front.
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Old 10-22-2007, 12:07 PM   #4
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Re: Plywood Direction Effect On Floor Bounce Over I-Joist


I can only tell you that I was taught to NEVER run with the joists. I always run 90 to the joists with the ply. Flooring, side walls same . 50% overlap. Subflooring is also always glued and normally screwed.
IMHO I believe that is why you have the bounce, ply running "wrong direction"
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Old 10-22-2007, 12:10 PM   #5
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Re: Plywood Direction Effect On Floor Bounce Over I-Joist


Also I believe by running solid bridging in center of span it may stiffen it up a bit. It will take the "roll" out of it at a minimum.
another mental note regards my first comment. You have run the long grain of the sheet with the joists and it should always be across the joists is another way to look at it.

Last edited by skymaster; 10-22-2007 at 12:13 PM.
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Old 10-22-2007, 12:38 PM   #6
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Re: Plywood Direction Effect On Floor Bounce Over I-Joist


ok , and your span is only 14 feet correct? if this is correct you are running into the fact that each piece of plywood is creating a bridge effect . meaning that every four feet a new bridge occours,the joists are not acting as one floor, acheived by over lapping plywood over 7 joists.the correct way was to run ply wood across joists. but thats a mute point now so heres a fix you should try . in the old days we use to only have 2x 12/10 for floor joists and we installed what was called bridging to stiffen the joists. they have metal or we used 1x4 or 2x4 scraps cut with an angle to seat againest the joist forming an x pattern. we would run these every 10 feet max. you would be nailing them into the flanges of the i joists. make sure that the two parts of the X do not touch each other or u will have squeaks ,that i can promise . use small nails like an 8penny or if ya have air stapler at least a 1/2by 1-1/2staple .i would suggest a hit with glue also to help with movement of the x on the joists.run two rows. another fix would be to take lvl or micro lams of same height added next to floor joists every third joist.becarful not to mis nail the flangesor bust up the flanges with to many nails. what ever you decide to do ,glue the heck out of any member nailed next to i joist cuzs i have fixed many a squeak do to wood on wood.
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Old 10-22-2007, 12:54 PM   #7
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Re: Plywood Direction Effect On Floor Bounce Over I-Joist


I agree with all comments above.. looking back when I hit the main beam in the front I should have changed direction over that beam...

Maybe I will start by stiffening one side of each ijoist with the gp rimjoist material and see where that gets me.
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Old 10-22-2007, 03:33 PM   #8
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Re: Plywood Direction Effect On Floor Bounce Over I-Joist


You ran your sheets perpindicular to the joists? So the tongue/groove edge of the plywood/OSB was nailed along a joist? If that's the case, you are going to have some troubles...For two reasons...One, if you are using OSB(I'm not sure about plywood), OSB is manufactured with a strength axis...If you turn the sheets, the sheets will begin to split and break after some time between the joists....Two, you have essentially railroaded the sheets, only having 3/4" attachment along every 3rd joist, not to mention that nailing along a tongue and grooved edge is basically not nailing at all.

I would suggest that if this is the case, then you should install solid bridging every 2 feet. Along both sides of the joist that the TAG seam falls, install an additional joist or nailer that attaches firmly to the joist....Then renail along the seams into the sistered joists/nailers.

I don't think that deflection is the biggest issue here, I think that I would worry more about the sheets being installed in an improper manner, that might give you more trouble than the deflection.

Also, you didn't tell us the spacing of the joists. Spans will change depending on how far apart you place the joists...If 16' 8" is for 16" centers, and you placed the joists at 24" centers, then your deflection will be far greater.
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Old 10-22-2007, 03:54 PM   #9
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Re: Plywood Direction Effect On Floor Bounce Over I-Joist


Quote:
Originally Posted by personalt View Post

Was not changing my plywood direction when the joists changed direction my problem here?
Your not supposed to run plywood with the joists, period. You've probably voided the warranty on the I-joists also by doing that.

Rip up that section and do it right. You wont pass inspection anyway.
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Old 10-22-2007, 05:20 PM   #10
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Re: Plywood Direction Effect On Floor Bounce Over I-Joist


I'm with Joe Carola here. I don't even think 16" blocking will help. When the plywood is perpendicular, it strenghtens the joist.
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Old 10-22-2007, 05:38 PM   #11
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Re: Plywood Direction Effect On Floor Bounce Over I-Joist


You F***ed Up. Plywood is springy across grain. Short of pulling it up and starting over, your only shot--the pain will help you remember how to lay plywood--is nail 2X4 blocks, flat ways, at 16oc between the top flanges. I'd tell you to put construction adhesive on top of them to increase your penance, but I'm not sure that'll be possible. Then nail the deck to the blocks. ply should be pretty stiff in 16X16 squares.
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Old 11-03-2007, 09:36 PM   #12
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Re: Plywood Direction Effect On Floor Bounce Over I-Joist


looks like you have learned your lessen and gained some valuable insight!... dont think i could add much more... just everything they said... it sucks but the best thing to do is rip it up and do it correctly... or brace the bajeebers out of it with cross members, except than is there plumbing and duct work running as well.... any way, im sure you have already addressed this and have started a new project by now... best of luck
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Old 12-28-2008, 08:04 PM   #13
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Re: Plywood Direction Effect On Floor Bounce Over I-Joist


JUST DO IT RIGHT. Thats what separates tradesmen from homeowners
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Old 12-28-2008, 09:12 PM   #14
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Re: Plywood Direction Effect On Floor Bounce Over I-Joist


Quote:
Originally Posted by personalt View Post
Is the direction of the plywood the major factor here?
Did I read that you ran part of the sub-floor with the 8' edges running parallel to the joists?

That would be a bad thing.

Go downstairs at your job site and read the bottom of the subfloor. It should have some words stamped on it that mention the strength axis. That means across the joists perpendicularly, not with them.

Gotta run for dinner. If I miss read this ...so sorry charleeee

okay...I'm back.

Sounds like one of those expensive lessons that we sometimes sign up for via brainfart or lack of experience. We all get hit by the Murphy stick on occasion. Betcha you'll never do this again.

My vote is
A. Rip up the wrong and do it right with new sheets
or
B. Look into sheeting over the entire floor again, on top of the existing plywood...but run the pieces the right way. Kinda expensive, and you need to not only shoot with framing nails all the way into the joists below...but it is good to screw the pieces together randomly in the field.

I only had to do that for one builder, who insisted on adding 1/2" CDX to the floors as the last thing we did as framers. We had to cut the pieces to butt into the walls and through the door openings. I don't know why he wanted 1/2" on top of 1 1/8"...I was just the helper back then.

Last edited by wallmaxx; 12-28-2008 at 09:32 PM.
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Old 12-29-2008, 09:51 PM   #15
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Re: Plywood Direction Effect On Floor Bounce Over I-Joist


Regardless of what the I-Joist industry says, I wiil not run 12" joists over 16', BCI has no limitations on subfloor or flooring direction, they give you the limits of thier product. If you read closely they also suggest a shorter O.C spacing for such applications. You will not viod any warranty, they will just tell you you used them wrong without thier engineering and , once again it's your ass. My advise, Install a mid point double micro-lam as thick as you can get, and still have adequate headroom at the mid point or close. Don't tear it out , just make it safe! Hey, you live you learn. Better thinking next time.
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Old 12-29-2008, 11:25 PM   #16
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Re: Plywood Direction Effect On Floor Bounce Over I-Joist


Running t&g parallel with the joists puts butt joints spanning the joist spaces also..butt joints should be on the joists. Your subfloor will sag and work the fasteners loose.
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Old 12-29-2008, 11:44 PM   #17
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Re: Plywood Direction Effect On Floor Bounce Over I-Joist


I know this is an old post...so here goes...

I would never run subfloor parallel, BUT it is not causing the joists (which the OP confirmed) to bounce. That deflection is a joist rating issue.
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Old 12-30-2008, 12:59 AM   #18
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Re: Plywood Direction Effect On Floor Bounce Over I-Joist


Its obvious that its not the joists bouncing/sagging...they don't care what direction they are set. They are stiff with NO plywood on them. Just walk on them before you start subflooring.

The plywood, on the other hand, is deflecting in between the joists and causing the floor to "feel" spongy due to the strength axis being parallel to the joists.


...and then...

That brings up another silly argument I get into with Canadians whenever I am framing up there. They run wall sheathing sideways rather than vertically. I've had two different CDN framers tell me that the walls are stronger because they run the strength axis of the plywood perpendicular across the studs.

I pull my hair out trying to explain that strength axis (fiber orientation) is only good for deflection...which on a wall would be a point loaded force either pushing into or out of the structure, on the plywood.

As far as lateral shear...plywood, in the 1/2 edge direction is the same either way...but once nailed to studs, it depends on how much of the edge is nailed to a solid framing member that accounts for shear strength.

Applying sheets vertically results in total edge nailing. In WA, it is a requirement that all edges be set against continuous framing. If we were to set plywood sideways, I would have to install 14 7/16" blocking at the plywood seam. No bueno man.

Add to that that the CDN code mandates a continuous mechanical venting of all closed pockets...so the horizontal sheathing also has to be gapped 3/4" to 1" from the next upper sheet.

Sorry for the thread theft....just had plywood on the brain.
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Old 12-30-2008, 06:31 AM   #19
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Re: Plywood Direction Effect On Floor Bounce Over I-Joist


Agreed on the walls Wallmax for all the same reasons. I have run into framers here and there in the US who insist on this too. They make me want to .
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Old 12-30-2008, 07:52 PM   #20
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Re: Plywood Direction Effect On Floor Bounce Over I-Joist


Maxx! I want some to agree with me that a 14 and 1/2" span that any sub floor even the cheapest will stand up?

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