I have a new home with a roughly 20′ square family room in which the floor shakes (vertically) and would like to reinforce the engineered I joists (We have plans to finish the basement room under the family room and I would greatly prefer to have no supports in the middle of the room. The I joists are 14″ deep and spaced at 16″. The builders source recommended 14″ lengths of 2×4 with ends of the 2×4’s nailed to the top and bottom flanges. One length of 2×4 would be nailed to each side of each I joist down the length of the room. Then 14″x14″ plywood panels could be nailed to the 2×4 thus spanning the space between the joists. This makes no sense to me for reducing the effects of vertical deflection. Wouldn’t “sistering” the middle of each I-joist with strips of plywood be more effective? If so, specifically how should this be done? Thanks in advance.
RT
Replies
I would be tempted to box them in with ply on the outside flanges, glued and screwed. Maybe just screws on one to try. I am sure if it's deflecting that much you will feel the difference immediately.
His problem isn't deflection. It's vibration.
Boss Hog has some reference links on this subject.
Presuming that these were engineered properly for load and span, I would add 20' long 2x10 to the middle of each with glue and screws to add stiffness and mass. Then I would apply strapping to the bottoms, perpendicular to the TJIs @ 16"oc to make the whole system into a tight sandwich. The long solid lumber might even be un-necessary, with the strapping doing more, at less cost, but once the strapping is in therre would be no way to addd the long solid lumber..
Excellence is its own reward!
Rip Sheets of 1 1/8" plywood into 14" strips and glue and nail to each side of the I joist at 6"OC. Where the Plywood splices, build up the I joist with plywood between the chords to provide edge nailing.
That's not a bad idea. Let's refine it some more. Make each a box beam by ripping 1/2"ply 14" and gluing ans tacking it to BOTH sides of the I-joist, alternating the butt joints.
The critical area of concern doing this is that of nailing to the top and bottom chord of the I joist. Poking tha laminated piece full of nails in a way that could make it "nail poor" could void a warrantee. That's why i say tack it instead of nail it. Just use fine small nails to hold well enough for the adhesive to take a hold. Probably a good idea to run it past the manufacturere too.
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Excellence is its own reward!
Edited 10/18/2002 6:05:45 PM ET by piffin
While I like the box beam idea, there are two problems we have here. The web and the bottom chord (as you described it) are the stressed members. Anything damage to the web will surely void the warrantee so nailing to the ply is out. If you score or damage the bottom chord (tensioned member) you can cause a failure. I don't know if nails are enough to do that.
Mike O.
That's why I suggested running it by the maker.
Excellence is its own reward!
Yesh!!!
If you can apply a finish material to the bottom chord of the wood I-beam you can surely apply some strapping. Simply strapping the underside (bottom chord) will help spread the load. Ideally you need to use cross bridging and strapping. Cross bridging is required at intervals not exceeding 7 feet.
And a little glue here and there will help avoid the squeeks.
Later
If you've moved furniture, etc. in, clear out the room to unload the joists before sistering anything on.
Some say the glass is half empty, others half full. I say "Just let me finish the %&$^ thing and pour me another"
I don't know all the details but on one job I know of the carpenters, evidently under the instruction of an engineer, glued and screwed plywood, 1/2" on top and 3/4' on the bottom, to the floor and the bare ceiling joists below. There was talk about this treatment greatly strengthening and stiffening the floor assembly.
The method your builder is proposing will spread the load from a single beam to several as you walk. Putting those bridges in ties the individual I-beams together. I would recommend putting in more than just a single row across the center..
If this was my problem, I would glue and screw the 2x4 uprights to a 14" square of OSB first. Then glue and nail the the OSB to each side of the I-beams. With 16" centers you can get a siding or roofing nailer in there to stick them on. After these are all in place, then glue and nail plywood or OSB on both sides of your 2x uprights to make a sandwich.
Keep the 2xs and the ply a bit below the subfloor to avoid potential squeaks? Joe H
can't be shaking that bad, 14"tji's @16" o.c, 20 feet, I recall jobs with joists like that, span at 2 feet oc, which made an acceptable floor, if you have the time to disconnect wires and pipes , you can buy the web filler to put in, which basically makes a microlam out of each joist, as mentioned before, don't nail into the chords. If it's too much work for you, you could look at the blocking again. It would certainly help.
listening for the secret.......searching for the sound...
I-joists that span 20' and are 14" deep shouldn't have much vibration. That's well within the acceptable range for that depth.
Several things come to mind - I'll just throw them out as they wander through my head.
First - A beam can contribute to the vibration of a floor system. What do each end of the I-joists sit on? If you have a beam that's overspanned, that might be part of the problem.
Dave makes a good suggestion about adding strapping. It could be the I-joists are twisting sideways a bit as you're walking across the floor. I've heard it called "torsional vibration", if you like impressive labels.
What stage of construction is this house in? Are you living there, is there furniture in the room, etc? Sometimes furniture and floor coverings can make a lot of difference. Even adding drywall on the interior partitions will dampen it a lot.
Are these I-joists just 20' long, or do they continue over another span? Sometimes double spanning I-joists or floor trusses can make a floor do funny things.
IMHO, adding plywood or lumber on the side of the I-joists is a waste of time. It might add mass, but is very labor intensive. You're better off adding mass on the bottom flange.
Piffin's suggestion of talking to the manufacturer is a good one. They've dealt with these situations hundreds of times, and may have some practical solutions. They may also have a rep that can come an look at the thing, which we can't do.
That's all that I can think of at the moment.
I won't rise to the occasion, but I'll slide over to it.
"IMHO, adding plywood or lumber on the side of the I-joists is a waste of time." (my emphasis)
Hey Boss, no need to be humble about that comment, it's 100% correct! - as is the following sentence in that post.
JH favorite method is lag bolting 1/4 inch steel plate to the bottom chord, but only when I find the bolts/steel as free scrap.<G>
I tend to agree. The poster didn't specify the brand of joists we're discussing, but I'm familiar with two kinds: TGI's (Weyerhaeuser), which has 3/8" OSB webs; and BCI's (Boise Cascade) which has 1/2" OSB webs. The engineered characteristics of each are similar, but there are subtle differences and if a customer wants to maintain the warrantee of a floor system, he's best advized to consult with the technical rep. for the manufacturer and get the solution from them...and have them fax or e-mail or snail mail a copy for future reference (CYA). And for building inspectors if they question what's been done (probably doesn't apply in this case).
I had some problems with some engineered products earlier this summer and found the technical people to be very forthright and helpful once I got past the sales rep.
Some of the suggestions that have come up sound OK at first glance, but the engineered products in general require pretty specific treatment for a variety of situations.
Boss, you must've been readin too fast and missed it but I think that I was the first to mention strapping in this thread in combination with the more expensive suggestion of adding solid continuous 2x lumber back in the third post.
The box beam thing keeps coming up in differing versions, but bake was first with it.
The more I study and think this through, the more certain i am that strapping is the only thing this needs to correct it. I am remembering one we did in about '89 where the design speced TJ15s or TJ 25s at 12"oc for a twenty foot span. We put strapping and SR on the bottom and there has never been a complaint. I have been in the house sveral times since..
Excellence is its own reward!
After reading Boss' reply, I had to review the original post again to see if I missed something. I'm not sure what you mean by "builder's source"
Source of gossip?
Source of I joists?
Source of general information
Source of engineering?
If we assume that he means the source from whom he buys the I-joists and that they also provide the manufacturers engineering, then we can assume that it is OK to nail sideways every 16" in to the flanges. We also learn that, in their minds, the way to stop this vibration is to provide the I-joist version of solid blocking, though the way they describe is kind of hokey.
There have beeen studies showing that placement of strapping at 16"oc on the bottom of a floor joist system does as much to add strength as does the old method of fitting solid blocking or bridging at 8' oc. Strapping is much easier and more economical to install.
Excellence is its own reward!