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Plywood direction effect on floor bounce over I-Joist

25K views 25 replies 14 participants last post by  Joe Carola 
#1 ·
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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#3 ·
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.
 
#4 ·
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"
Jack
 
#5 · (Edited)
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.
 
#6 ·
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.
 
#8 ·
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.
 
#11 ·
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. ¾ ply should be pretty stiff in 16X16 squares.:rolleyes:
 
#12 ·
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
 
#14 · (Edited)
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.
 
#15 ·
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.
 
#18 ·
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.
 
#21 · (Edited)
there is no grain in obs or any pressed product. Staging a lam at the mid point or close reduces deflection to almost nothing. read you stuff. lateral movement is gone with brid
ing. :laughing::laughing::laughing::laughing: Think before you speak? ugly dog also?


OSB
=

oriented strand board...the fibers are laid down somewhat directional in the glue before pressed. Over 14 1/2", the plywood is weaker one way than the right way.

I just went through this last week, decking a house. The cut guy was trying to use up all the scrap rather than cut full sheets. He sent me up a triangle cut from the plywood in the wrong axis direction. I asked for a new piece and had to explain that it was too weak to walk on.

Sorry B-man. "Your data on the Mig is inaccurate."

And what's with dis'in a man's dog? Be nice...be professional.
 
#22 ·
there is no grain in obs or any pressed product. Staging a lam at the mid point or close reduces deflection to almost nothing. read you stuff. lateral movement is gone with brid
ing. :laughing::laughing::laughing::laughing: Think before you speak? ugly dog also?

OSB =

oriented strand board...the fibers are laid down somewhat directional in the glue before pressed. Over 14 1/2", the plywood is weaker one way than the right way.

I just went through this last week, decking a house. The cut guy was trying to use up all the scrap rather than cut full sheets. He sent me up a triangle cut from the plywood in the wrong axis direction. I asked for a new piece and had to explain that it was too weak to walk on.

Sorry B-man. "Your data on the Mig is inaccurate."

And what's with dis'in a man's dog? Be nice...be professional.
1 Question, why are all you GC's on the framer forum? You screw us down on footage and then come here to rub it in on how stupid we are!! Nathan needs to create a forum for GC's who are all about themselves. I may get cut and thunked as the mod said, but I'm not backing down from GC's who no nothing!!
 
#23 ·
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 plywood 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
The joke is you!
Doesn't matter how many micro-lams
one puts under joist, if the plywood
runs the wrong way.
BTW: The OP is 14 months old.
Maybe it's been taken care of?
there is no grain in obs or any pressed product. Staging a lam at the mid point or close reduces deflection to almost nothing. read you stuff. lateral movement is gone with brid
ing. :laughing::laughing::laughing::laughing: Think before you speak? ugly dog also?
I don't know about "obs," but OSB
is called Oriented Strand Board, and oddly it is oriented.
However you are the only one talking about
OSB.
The OP referred to plywood, or didn't you notice?
 
#24 ·
http://www.fpl.fs.fed.us/documnts/fplrn/fplrn059a.pdf
http://www.tecotested.com/techtips/pdf/tt_plywooddesigncapacities
http://www.tecotested.com/techtips/pdf/plywooddesignapplicationguide
http://www.lowes.com/lowes/lkn?action=howTo&p=Build/GdPlWd.html
http://www.apawood.org/pdfs/unmanaged/strucii.pdf

They all say the same thing. Plywood has a strength axis:

Sheets and/or layers of veneer are typically oriented with their grain at 90 degrees to each other and arranged in an odd number of plies or layers, resulting in a structural panel that has its greatest strength axis in the direction parallel to the face grain (typically the 8' direction).

And as stated before and seems to be overlooked, if H clips were not used the bounce could be from the lack of a lock between the individual sheets of ply since the T & G is over the 8' length. The bounce may have been between those sheets and not the entire floor.
 
#26 ·
Originally Posted by Joe Carola View Post
Your not supposed to run plywood with the joists, period. You've probably voided the warranty on the I-joists also by doing that.
So when you spout off about plans and spec's and engineers, and then in the next word say the framer has to check everything or he's ****. Just think to yourself, AM I REALLY A GOD OF CONSTRUCTION, or just someone blowing thier piehole!!!!! To me your a joke.:laughing::laughing::laughing::laughing::laughing:
I said probably because about 16 or 17 years ago when we started using I-joists this came up in a conversation one day when some homeowner ran the plywood with the I-joists and a builder who was a framer for 20 years before that said that he thinks that it would probably void the warranty.

It was the first and last time this ever came until this thread because no one ever runs plywood with the joist that I've ever seen whether you use I-joists or 2x joists. Will it void the warranty, I really don't know or care because it would NEVER be an issue, or be talked about.

As far as your other comments, you talk like your 10 and obviously are ignorant and lack social skills and you apparently think who you are when it comes to framing, I don't. Your thread about, "I'm new to this forum" was a complete joke and you embarrassed yourself.


borat_borat1950 said:
I am a framer. This is a framing forum, where do people like carpenters, remodlers, roffers,(yes I spelled it right), BUILDERS (THE WORST), and anybody else who is not a framer, get off on giving us framing advise!!!
I will take advise from anyone who is not a framer if they give one and it sounds like a good one. I don't think I'm above anyone or that juvenile thing you said, "God of construction" or whatever. You said this because I just said that a framer should know how to frame the correct size stairwell? That's all it was, plain and simple!

Do you want to sit here and try to go toe to toe with me as framers or do you want to try and compare notes and help each other out with anything that has to do with framing? Or, do you want to keep talking like this?

Just think to yourself, AM I REALLY A GOD OF CONSTRUCTION, or just someone blowing thier piehole!!!!! To me your a joke.:laughing::laughing::laughing::laughing::laughing
 
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