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Old 12-28-2010, 09:20 PM   #1
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bracing floor joists - wobble wobble


Hello everyone - this would be my first post. I've been reading on the forum a long time and have gleaned much of what I've practiced in my home from this website - great resource. Intro to come later

For now, I have reached my boiling point with my floor. This is my first owned home, though I've done a lot of flooring (wood/stone/tile...etc), I have never wanted to invest into something like this until now. I will try to give a brief history so its not a tough read; please excuse my laymen terms for everything - I have been searching images/posts to try and find similar examples and terminology but have come up short.

We've a "great" room in our home that is about 18 x 22 that shakes (which I believe is deflection) quite a bit - even with my 120lb wife walking normally across the floor. The floor joists run the full 22' and are spaced 24" OC. From what I have read this is pretty paltry construction. These are cheap homes in my neighborhood (Longmont, CO) and the construction date was 1977.

I've read a ton about bracing the joists and was all amped to do it until I went down in the crawl space and found out they are not your typical 2x8 or even 2x6! They are constructed like "I" beams in that the vertical piece is 5/8 plywood that is sandwiched on top and bottom with 2x4's. The top 2x4's run the full length and are the ones that are resting atop the concrete footers (all 22'+!!!). So all that is supporting my floor are these (2) 2x4 sandwiching some plywood that drops down about 2' and has another set of 2x4's sandwiching the plywood at the bottom (all forming an "I").

There is seemingly random X bracing and some cripples that do not look ample. Atop all this is 3/4 hardwood (sub floor) and then either 5/8 teak laid diagonal (80% of house) or my kitchen which is all backerboard and travertine. As soon as you step onto the teak and do anythign but tip toe, the cabinets shake and the crashing/stomping sound ensues. Driving us nutts! I figured since the tile in my kitchen seemed pretty sturdy I could just go underneath and brace the joists from the bottom by running some 2x4's on the diagonal (opposite flooring so they are perpendicular) all over the place on the bottom of the joists (about 4' apart).

After reading and reading about other folks' issues with this it seems sistering is the way to go. However I don't really know what the best way to sister these types of floor joists would be. Perhaps I can just run another 2x4 set the length of the joists: one under the top one and one above the bottom one and secure them with metal plates to the existing ones?

Now here is the part where I will get reemed: we removed a "L" wall that was right in the middle of this room. Non load bearing wall, but obviously it made up for some rigidity in the flooring of the home and the bouncing was not really realized as we didnt' live in the house prior to the demo of this wall.

Any help? I am happy to take ANY pictures that might make this easier.
I've got lots of tools and I love having an excuse to buy more - plus I can likely borrow just about any type of nailer or anything I might need to get this done quickly. I'd really just like to know the most effective way to tighten up this floor in this house. I've had a thousand ideas but I am not an architect nor carpenter/contracter (auto mechanic) and I'm sure there are plenty of you out there.

Thanks so much in advance. I'd love to hammer this out this weekend and get this house feeling a bit more solid.

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Old 12-28-2010, 09:56 PM   #2
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bracing floor joists - wobble wobble


If you are getting that much deflection from the floor, you need to get an engineer. The I-beams are actually very good support, better than just 2x8 or 2x10 beams. Sounds like there are more problems that you caused by just removing the L shaped wall. Really need to take pictures of the space down below showing wall to wall how the beams are laying. There should be a Steel I-Beam with Lolly columns supporting it aprox. every 8'. If it was like this before the purchase, you really need to talk to both a Lawyer & engineer. The local building department should have the contractor plans, and permit info available also, so also may want to talk to city hall.

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Old 12-28-2010, 10:24 PM   #3
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bracing floor joists - wobble wobble






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Old 12-28-2010, 10:29 PM   #4
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bracing floor joists - wobble wobble


Granted that may be the route someone else would take - that is not necessarily the reason I came on here with these questions.

I don't know it all but I bet there is a DIY solution to this and that is what I hope to get! The wall I removed was not load bearing in any way - as much as I would like to say that there was wobbling before and I didn't do it, I cannot be 100%. We came into the house as pretty nasty foreclosure that needed LOTS o work. Had contractors and archi tell me the walls were fine to remove (since there are full truss' and everything spans full length I believe they were correct).

Hoping these pics will show enough for someone to help me out. Obviously these are not steel I Beams - nor should there be any. The construction of these joists seems flimsy to me, but perhaps I just an inexperienced. I was originally planning on insulating and reinsulating between the joists and then running some 2x4's along the bottoms of the joists (screwed in) on a diagonal to try and help. I would rather try to do something right the 1st time.

Last edited by noahrexion; 12-28-2010 at 10:32 PM.
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Old 12-29-2010, 07:12 AM   #5
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bracing floor joists - wobble wobble


There is no DIY solution to your problem. You need to get an structural engineer in to look at your home. No one on the Interwebs is going to replace the knowledge, or take the liability of your situation. Do yourself a favor, contact a good structural engineer in your area, and head down to City hall to the Buidling Dept. and look through the permits, etc, and if plans are avail. they should show if there was to be a Steel I Beam as I had mentioned before, to support the beams as they pass through the middle of the house.

You may think that they are flimsy construction, but Engineered I Truss systems are a lot more sturdy, than 2x8 or 2x10 joists, as mentioned before. Get an engineer in there, before you have more problems, by doing it a "DIYer" with no knowledge fix, that can do more damage.
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Old 01-21-2011, 11:33 PM   #6
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bracing floor joists - wobble wobble


With a couple of short column jacks and 4x6s you could set up a temporary girder in the middle of the unsupported span. If that seems to solve your problem, you could add a built-up girder, heavy duty column jacks, and concrete footings. Look over the prescriptive code and take a sketch to an engineer if you like. A PE here will stamp your sketch for roughly $200, but the building department where I live doesn't require a permit for reinforcing an existing structure.

Two areas of concern:

1) Those don't look like any I-joists I've seen. They look like something your builder put together on site. I really doubt they were certified like prefabricated I-joists. I'm not engineer, but I think you need a solid strip of lumber along the bottom of the webbing.

2) In one of your pictures, your joists seem to have been butchered to accommodate ductwork. In my opinion, your HVAC sub destroyed those joists by putting a colossal notch in the middle third of the span.

Interesting read (starting on page 34):
http://books.google.com/books?id=iwSasc7rowcC&pg=PA35&lpg=PA35&dq=sold+str ip+under+I-joist+webbing&source=bl&ots=QXrsP2boh2&sig=toTAeIr CBMc17y0y0vpqTwp90i0&hl=en&ei=M2s6TbfQN8KqlAfIyYnc Bg&sa=X&oi=book_result&ct=result&resnum=2&ved=0CBY Q6AEwAQ#v=onepage&q&f=false


Last edited by benjamincall; 01-21-2011 at 11:50 PM.
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