# TJI Saggy floor fix?



## Kent Whitten (Mar 24, 2006)

I have some wicked crowned stuff that would take that sag out no problem :thumbsup:


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## neolitic (Apr 20, 2006)

loneframer said:


> Just curious Tim, how would laminating 3/4 plywood, lets say typical CDX, on both sides of the joist, rate as a solution? Let's assume glued and nailed with 12D commons, staggered on 12" centers.:thumbsup:


That's the deal, maybe Spax lags
rather than nails.
I was addressing his desire to use
the material on hand.
Still think sandwiching with his
webs would be stiffer than using
the chords....


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## loneframer (Feb 13, 2009)

neolitic said:


> That's the deal, maybe Spax lags
> rather than nails.
> I was addressing his desire to use
> the material on hand.
> ...


Problem with the webs, IME, is that they are jointed every so often, maybe 4'. Not sure if all manufacturers are the same. Without the chords, not much structural integrity.:thumbsup: You can almost pick them out on some of these rafters. Look for a dark line perpendicular to the flanges.


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## BldgMatlsGeek (Jul 7, 2010)

Never cut into the flange of an I-joist....much to the dismay of plumbers and electricians. You could use LVL, but then you run into the problem of not being able to run any mechanicals thru them. You can buy 3-1/2 2.0E LVL from Georgia Pacific, normally used as a tall wall stud. Good luck and.....wear a hard hat.


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## neolitic (Apr 20, 2006)

loneframer said:


> Problem with the webs, IME, is that they are jointed every so often, maybe 4'. Not sure if all manufacturers are the same. Without the chords, not much structural integrity.:thumbsup: You can almost pick them out on some of these rafters. Look for a dark line perpendicular to the flanges.


Aaaah, I *ass*umed that they cut
all of those out of 10' stock....


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## dave_dj1 (Mar 16, 2010)

all the tji's I have used have laminated top and bottoms, I think the OP could do it his way, after all the 2x4's have been there for 60 yrs. I'm no engineer but I would try it his way, can't hurt. If I understand him correctley, he is going to make up his own tji's by ripping and putting two pieces side x side , i think it will work.


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## loneframer (Feb 13, 2009)

dave_dj1 said:


> all the tji's I have used have laminated top and bottoms, I think the OP could do it his way, after all the 2x4's have been there for 60 yrs. I'm no engineer but I would try it his way, can't hurt. If I understand him correctley, he is going to make up his own tji's by ripping and putting two pieces side x side , i think it will work.


 You jarred my memory of a time when we needed to rip 12" TJIs to about 10.5" to match up a bastard hip. We ripped the cord off, re-dadoed it to receive the web and rebuilt it to the size we needed. The longest rafter was about 10' and it did the trick. I think in this case, it may be cheaper to buy new material than to remanufacture I-joists though.:laughing:


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## Tim Garrison PE (Oct 22, 2009)

loneframer said:


> Just curious Tim, how would laminating 3/4 plywood, lets say typical CDX, on both sides of the joist, rate as a solution? Let's assume glued and nailed with 12D commons, staggered on 12" centers.:thumbsup:


That's a good, not great, way to do it. The problem is not enough meat is added to the tension and compression (bottom and top) parts of the joist, and too much is added to the shear (middle) part.

Plywood is generally stronger than sawn wood so adding 3/4 + 3/4 = 1.5" of it to the joist would be a significant improvement, no doubt.

Really, the best remedy is to add depth, like a 2x10 sistered. As I've written before, bending strength goes up geometrically with depth. So a small increase in depth gets you a big increase in bending strength.


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## Joe Carola (Jun 15, 2004)

Tim Garrison PE said:


> That's a good, not great, way to do it. The problem is not enough meat is added to the tension and compression (bottom and top) parts of the joist, and too much is added to the shear (middle) part.
> 
> Plywood is generally stronger than sawn wood so adding 3/4 + 3/4 = 1.5" of it to the joist would be a significant improvement, no doubt.
> 
> Really, the best remedy is to add depth, like a 2x10 sistered. As I've written before, bending strength goes up geometrically with depth. So a small increase in depth gets you a big increase in bending strength.


Tim,

Would 9-1/2" rips of 3/4 plywood on each side with a full length 2x4 on edge in between the plywood flush at the bottom glued and screwed work? Or, two layers of plywood on each side?


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## Tim Garrison PE (Oct 22, 2009)

Joe Carola said:


> Tim,
> 
> Would 9-1/2" rips of 3/4 plywood on each side with a full length 2x4 on edge in between the plywood flush at the bottom glued and screwed work? Or, two layers of plywood on each side?


Yes - now you're talking! That arrangement could probably span 15' and be rock hard. But, of course, it'd be a pain to make and would violate the original guy's issue of no additional depth.


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## Joe Carola (Jun 15, 2004)

Tim Garrison PE said:


> Yes - now you're talking! That arrangement could probably span 15' and be rock hard. But, of course, it'd be a pain to make and would violate the original guy's issue of no additional depth.


Forgot about the height. Wasn't thinking.


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## macrylinda1 (Jul 28, 2010)

angus242 said:


> Did you say 2x4 floor joists??????????????


well, what do you think of my tgi sandwich?!?! the only reason i want to do this is because i have 4 skids of tgi at my shop


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