Without a span table, my suspicion is that the I joists in a home are right at the limit of acceptable or they would not have passed. That notwithstanding, when the homeowner walks through the living room, the TV moves, the china rattles, etc. I can go in the basement and look up as he walks and see the whole thing flex. With all the wiring and plumbing runs in there, adding joists probably isn’t an option. It seems I read of a way of stiffening things up by ripping OSB, glue & screw. On the right track here? It seems plausable in theory. I’d like a reference if anyone has anything they’ve read or done. Muchas gracias
“The child is grown / The dream is gone / And I have become / Comfortably numb ” lyrics by Roger Waters
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Can a beam be added midspan? Need some footers for the lallys, but would certainly solve the problem. Not really sure that rips of OSB will help so much....but I've been wrong before!
Out of curiosity, what size are the I-Joists? Span?
I agree that shortening the span with a beam is the best solution. We often frame a wall about 6 feet from the foundation which can be used for shelves and storage in the basement.
It takes a lot of work to take out the tremors that cause dishes to rattle. Boss Hog can explain the whys of this, but it has to do with the depth of the floor system.
The joists are LPI (Louisiana Pacific) 12" depth. The spacing is 19 1/4 - someone used the black triangles! The span is 14ft.
The gameplan inasmuch as the HO is concerned is finish the basement, but by and large it will remain a predominantly open floor plan. I love the idea of splitting the span with a wall but that's not necessarily what he wants.
Just to clear up misunderstanding - it's not one or two joists that move. The whole place, from the bedroom to the kitchen, the living room, the bath on the other side. It's springy. Not good."The child is grown / The dream is gone / And I have become / Comfortably numb " lyrics by Roger Waters
You are looking in the wrong place.
According to the tables 12" LPI-26s @ 19", 40# live/25# dead, and 1/480 deflection will span 17'-7".
Under the same conditions 10" LPI-26s will span over 14'.
Neither should cause vibration at that span. Look somewhere else for the problem.
He did say something about wiring and plumbing runs up there...
Perhaps they had their holes cut too large or in the wrong location?
It dawns on me that this construction is a lot like my garage.
My garage has 1-1/2" x 12" I-joists @ 16" (yours are 19"). They span 26' with a center wall at 13'. (You have 28' span with a center wall at 14'.)
With 3/4" ply nailed and glued my floor specs at 100#/sqft at failure.
Without any ceiling below I could drop bundles of shingles on the floor without any vibration. Before that without the sidewalls up there was no vibration of the floor.
I don't think there is a cost effective way to fix your floor.
You shouldn't be having trouble with a 12" I-joist spanning 14'. Somehting's gotta be wrong.
An underdesigned beam can cause problems with a floor system. What type of beam are you dealing with? Beam size, post spacing, etc.
The idea of adding 2X4 strapping on the bottom of the joists might make a difference. If you put 'em on with screws they can easily be removed later if they don't work or if you need to try something else.
The ideas about adding plywood to the sides of the joists is probably a waste of time. I doubt that would accomplish anything.
Adding plywood to the bottom might help, but so would adding drywall. How much difference it might make is anyone's guess.
One more thing - What's the span on the OTHER side of the beam? You say it's 14' where it's bouncing. I assume there's a beam that the I-joists cross. What's on the other side of the beam? Another 14' span, or is it longer, shorter, or what?
Any chance you've got a digital camera, and can take some pictures?Please don't lie to me, unless you're absolutely sure I'll never find out the truth. [Ashleigh Brilliant]
The bearing wall is more or less center of the space. Joists running the short direction of the basement, 28ft width, so it's 14ft from bearing point to bearing point. If you walk over the bearing wall, you're fine. If you're in the middle of a room on either side . . .
I'd like to chip in and say thanks though. Lots of good ideas flying about. "The child is grown / The dream is gone / And I have become / Comfortably numb " lyrics by Roger Waters
What about the beam itself? You didn't give us any info on that.I was thinking that women should put pictures of missing husbands on beer cans.
Beam - one end of each Ijoist rests on the foundation wall, the middle is supported by the bearing wall, the other end is on the foundation again. The bearing wall is 10' in height, 2x6 16"OC with blocking."The child is grown / The dream is gone / And I have become / Comfortably numb " lyrics by Roger Waters
So there's no center beam, right? You have a bearing wall running the length of the basement?
The whole thing just doesn't sound right. I can't imagine why a floor like that would be springy.
One thought to add - If you talk to the place where the I-joists were bought from, they may be willing to have a rep from the manufacturer come out to look at them. I've had that done a time or 2 when there have been problems. Doesn't cost anything, and couldn't hurt.Blessed are the censors; they shall inhibit the earth.
Is it possible that the top and bottom flanges are not the same, and that the joists are installed upside down? A beam with a smaller top flange, intended to be reinforced by the underlayment (assumed glued and screwed) would have a much smaller moment of inertia if installed upside down, and therefore be more springy in service than intended.Be seeing you...
I haven't seen I-joists yet which have to be installed with one side up. Every brand I've dealt with can be turned either way.My hockey mom can beat up your soccer mom.
well with all these different ideas I'm now totally confused.....and my rep telling me I need no x bracing or strapping on 32' 16" 500 seious TJI's with no center supports.
a
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Andy, what is your criteria? Ultimate stiffness, or stiff enough cheaply?
In order of stiffness and aproximate cost (ascending)(All SWAGs)
1x4 strapping 8'oc
metal x braces 8"oc
1x4 strapping 4'oc
metal xbraces 4'oc
1x3 xbraces 8'oc
metal xbraces 2'oc (minimum I would use, still some slight vibration)
1x3 xbraces 4'oc
1x3 xbrace and 1x4 strapping 8'oc aligned or:
solid or I-beam blocking 8'oc
1x3 xbrace and 1x4 strapping 4'oc aligned (stiff enough for normal house use, add 1x3 strapping between 1x4 for 5/8"DW ceiling; also adds stiffness)
1x3 xbracing 2' OC
solid or I-beam 4'OC (Real solid and good DW backing) or:
1x3 xbrace and 1x4 strapping 2'oc aligned (Real solid and good DW backing)
And now for a major jump in effectiveness
2x4 perimeter block 8'oc and 1 layer 1/2" ply/OSB (Dance hall)
2x4 perimeter block 4'oc and 2 layer 1/4" ply/OSB or:
I-beam perimeter block 8'oc and 1 layer 1/2" ply/OSB
I-beam perimeter block 4'oc and 2 layer 1/4" ply/OSB (Dance hall, piano and band, w/ RH, 2" concrete base and tile)I would not use any less than minimum reccommended unless cost was the primary factor and it was required by an authority.
Maybe this will help clarify all the choices available to you and help you decide. anyway I hope it does.
SamT
a phone number would workMy life is my practice!
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My lumberman (ex-contractor) told me that he was taught to put a piece of galv flashing between layers in any built-up beam. I imagine that was before quality construction adhesive was available, but it makes sense to me. I don't know if something like PL Premium sticks to galv metal or not, but what do you think about the idea in general (I am considering it between 2x12s put together for a beam)Any jackass can kick down a barn, but it takes a carpenter to build one.
It would stiffen it, I don't know how much.
If I did that I would use 2 heavy ga, 14 or 12, 1 on each side of a piece of 7/16" or 1/2" ply.
2x12ga is almost 1/8" and that is pretty stiff stuff.
Like you, I don't know if glues would stick for very long to the galvy. Lots of bolts, maybe.
SamT
I wasn't being clear. The suggestion was to put common flashing between two (or more) 2x12 wood framing members.Any jackass can kick down a barn, but it takes a carpenter to build one.
why not just a flitch plateMy life is my practice!
http://CLIFFORDRENOVATIONS.COM
I think what he was suggesting to me was essentially a cheapo commonly available version of a flitch plate, only much thinner than such plates might normally be. In practice, I've only read of a flitch beam. Never have run into one.Any jackass can kick down a barn, but it takes a carpenter to build one.
I agree with the previous two resopnses. Except, I'm not sure that you would need any more concrete under added columns. I doubt that the point load would be that great, if the wood floor is already engineered to take the load. Most of the load is already going to your engineered support (foundation wall and center load beam).
Having said that, a 16" x 16" pad under each post is a minor expense.
Allow me to toss two pennies into the fray. By your description, I assume that the bottoms of the I-joists in question do not have any lateral support. That is they are not sheathed with drywall or something along those lines. I have framed a few houses where the bottoms of the joists are open. We always use Trus-Joist and the factory requires a strapping perpendicular to the joist at about 30'' centers to tie everything together. We normally use 2x4's, shot on with our nailers. This makes a noticeable difference. I became aware of this when we too had a homeowner whose china hutch rattled as he walked across the floor. This strapping took care of 95% of the problem. Get in touch with the manufacturer and talk to a service rep. Also ask for a span table, I'm sure they will send you one. This is a manufactured product and the guy that designs them and makes them is your best source of information. Good Luck.
why don't you take this problem to the supplier? lumber co may not have engineers but the i joist people do.
I built my house using SP35 11 7/8" Truss joists 24" O.C. In areas where flexing would be a problem I sistered (glued and screwed/nailed 3/4" CDX to the joists. The idea is to fasten them from top cord to bottom cord. I also nailed in spacers every 2 to 4 feet where accessable to complete the stiffening of the joists. Essentially this created a "boxed-beam" effect rather than an I-beam. I also nailed in some 2x12 blocking ever 2' to 4' where I could to further stiffen the floor system. The ceramic tile was then laid and people swear it's on concrete! They are amazed at the strength of the floor. Several years after I finished the house I had an engineeering grad student run some tests at Penn State for me to see what the loads would actually be able to hold. After breaking a couple hundred bucks worth of material we figured that my floor has a loading factor of 195 lbs dead weight!! I feel very comfortable with using plywood reinforcing in most any construction situations now.
If you want to really stiffen things up. . .
Set perimeter blocking at 4'OC and sheath the bottom of the joists with ½" OSB or Plywood. Glue and hand nail with 8d 4" OC around the perimeter and 8"OC in the field. Stagger the joints. Make sure there is not a bow in the joists before you sheath.
Your client can park his car in the living room to work on it. . . assuming the wife doesn't shoot him first.
SamT
I built my first house with TJI's SP35's at 24" O.C. in areas where flexing would be a problem I sistered (glued and screwed/nailed) 3/4" CDX along a side from top cord to bottom cord) of the joists. Essentially I converted the I-beam into a Boxed-beam. I also nailed in some 2x12 blocking at 2 to 4' intervals where I had accesibility around ducts and plumbing. When the tile was laided the floor was so stiff and level guests thought it was on concerete. They couldn't believe my floors were so sturdy that couldn't believe there was even a basement below. A few years after I completed the house I had an engineering grad student run some tests at the local university. After smashing a few hundred bucks of material we calculated that my reinforced joist system had a sustain dead loading of 195 lbs! I have never since worried about reinforcing TJI's with plywood.
Sam
Interesting.....but I'm installing some 14" THIRTY footers (500 series) above a garage with a room above it.
I call the manufacturor and ask if I need x bracing. They tell me NO!
I can't believe that, so I decieded to use metal cross bracing every eight feet like one would with regualar 2x material but now I see you guys talking about every 30-48". whats up with that?
My guess is I may be better off with I-joist bridging rather than metel bridging.Are web fillers required? My phone rep tells me putting nails where they aren't required messes with the integraty of the TJI's and causes squeeks.
Theres a good article in JLC about strapping this month.
Would you install the strapping under or over the TJI's? Seems you need to route out the subfloor if you do it ontop......think thats right? what a hassle! If you do it below.....how does that effect the sheetrock?
Be well
andy
My life is my practice!
http://CLIFFORDRENOVATIONS.COM
Andy, the subfloor IS the bracing on top, and it is a diaphram, so it is better than any spaced bracing or stiffener.
Putting a 'subceiling' underneath is also a diaphram and is also better than any spaced type. It makes your floor a box beam.
When you diaphram both top and bottom, the floor acts like a drum. a drum is diaphrammed with soft sheepskin, yet it is strong and rigid enough to stand on.
I said 48" 'cuz I was talking about perimeter blocking for the diaphram. Ideally the diaphram sheathing should run parallel to the joists, but in this case, his joists are a cubit OC and it will use much less material to run them across the joists.
X-bracing and I-joist blocking both serve 2 purposes. . . prevents the joist from racking and spreads the point loads from one joist to the one or 2 joists on either side of the point load.
Pressure and perimeter blocking also prevent racking 'cuz they take racking forces out to the walls, and the walls won't rack.
If floor stiffness is more important than time and money, use x-blocking blocking in line with the perimeter blocks and sheath the bottom. I-joist blocking can act as pereimeter blocks themselves.
SamT
If you figure the allowable deflection in that span, (1/480) it is roughly equivalent to 3/8" over the 14'. This is normal but your record player will skip especially if you start dancing.
A double row of bridging will help share the loads and strapping 16" OC will also keep the bottoms from deflecting under load. I can't believe everyone does not strapp before sheetrocking. The Japaneese have been using multi layered floor systems for centuries, (earthquakes).
Hopefully you did not have a HVAC guy with a chainsaw working there.
That is a good point that wasn't addressed. How and where were any cut-outs through the joists performed?! I had a moron of a plumber cut right through the top cord of a TJI when attempting to install the drain for a bath tub. Another time I had a know-it-all "electrician" almost cut right through the entire flange from top cord to bottom cord. Whatever he was doing with a Sawz-all I still haven't figured out! The manufacturers detail specific places, shapes and sizes for cutting through TJI's. If you violate those specs, you void any and all warranty of those joists and come what may if they fail. If they are notched through improperly the only thing you can do is to either 1) add another joist next to them or 2) thoroughly sister them with plywood as I mentioned earlier. Adding a beam underneath still won't do the trick. Improperly notching through TJI's compromises their structural design integrity in the entire floor system.
My theory is that all you need to do is run plywood across and UNDER the trus-joist. The deflection is more across the joist, proof is the rattleling furniture is on the wall parallel to the joists not the wall where the joist rest.
So just install the first sheet of plywood (the thicker, the better) in the center of the room, across the joist, jack it up to hold it-prestress the floor and then nail or screw. Stagger the rest of the plywood and make cuts to avoid the mechanical projecting lower than the joist.
I don't have a reference, but your idea of stiffening up the joists by adding plywood or OSB (and thicker is better - do no less than 3/4-inch) has merit. If you do, you should do the middle third of each joist - no need to really do the whole joist. What you are doing is adding to the joist's section modulus and moment of inertia, which directly affects bending stresses and deflection. The size and spacing of the screws also is important as these transfer stresses to your new web. (In other words, screw and glue the hell out of it.) IMHO, I would try this first on a few of the middle joists and have someone walk on that stiffened portion and see if it is satisfactory. Adding straps as some have suggested will help some, but really, that is also adding weight, and not adding anything to your joist's structural properties. (Strapping limits lateral movement of the bottom chord of the joists.)
Some of the posts have stated that your floor system should be good for the span/deflection characteristics of your joists. This may be true for STATIC load cases. However, what you are describing is DYNAMIC floor response, and that is something else entirely. It depends mostly on span, mass and stiffness. But there are some technical variables which may cause a resonance or amplification which you are probably experiencing. What you want to do is stiffen your floor system. The absolute best way is to add a middle support and shorten the span. Short of that, what you suggest is also viable. However, the web you add must be continuous, and it sounds like there are a lot of conduits and such passing through the joists (although, they should not be inthe middle third of your joists).
Edited 10/30/2003 12:23:13 PM ET by KAORISDAD
The ide behind diaphramming the bottom of the joist uses the concept of increasing the tensile resistance to stretching rather than adding mass.
Assuming that Mylar did not stretch, you would see a larger increase in stiffness from bonding a taut piece of Mylar to the bottom of the joists than after adding ¾" plywood to the Mylar diaphram (theoretical) that you already installed.
In other words, any plywood thicker than ½" or 7/16";"is aready on the downward side of the cost/benefit equation.
A better way to increase stiffness beyond ½" ply is to double 3/8"" and offset all joints in the 2 layers, keeping in mind that you need perimeter blocking for both layers and those are the seams you most want to offset.
Don't screw, screws have too little shear strength. Use 8d or 10d nails, 4"OC perimeter and 8"OC field, hand driven to pull the ply tight to the joist.
It does depend on diaphramming the entire area rather than just the middle 2/3 or 3/4.
Adding mass can be done in just the middle but you're better off adding ¾" ply to the side of the joist if you are just adding mass.
Unless there is a bow in the floor, you won't need to "jack it up". If the floor is bowed!?!?! don't jack it past straight if diaphramming.
SamT
I believe the idea was adding a plywood web to the side of the I-joists to stiffen them.
Lots of good ideas here guys, if you load the middle of the i joists with plywood, apply diagonal bracing and strap it, you will be golden. The point is to add beef and create on "box" or beam which will be stronger. Personally I would start with the strapping and diagonal blocks or straps as described earlier. Good Luck.