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Old 10-24-2011, 12:27 AM  
papakevin
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Default Help with bouncy floors

I've got a house that I'm fixing up over time, and I'm looking for some help.

Long story short, bought it distressed, fixed foundation issues in back of house and replaced subfloor. Had major plumbing issue and crawl space completely flooded (had 4 feet of water in it). Pumped water out, dried it out over the next week, and now three months later it seems floors are bouncy in living room where the original floor was and kitchen where I replaced subfloor.

Looking under house, everything looks ok. House was a kit house from the 40's, and all wood looks good. The 2x8 beams connect to center support, which has concrete blocks supporting it every 7 feet or so in the middle of the house. Wondering if water flooding crawl space made blocks settle. Have small access to crawl space via the closet and trying to avoid tearing up original hard wood flooring to address issues. Might be able to punch out vent screens along side of house to allow for additional boards to be feed into space so they can be sistered onto the existing 2x8s, but don't know if that's the best course of action.

Question if adding additional supports to main beam in between the existing blocks would help. Have thought about adding cut 2x4s as cross bracing in between joists at bottom of joist (to help stabilize) and transfer weight to adjacent beams, but don't know if that would work. Have also thought about adding a middle support to help offset flex in living room, but thinking this may not be best plan either.

Looking at options, so any help is appreciated.



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Old 10-24-2011, 02:19 AM  
nealtw
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You didn't say how long the floor joists are. In new construction, we always use 2x10, and when the span is over 16ft the engineers often call for double floor joist or changing to 12" on center. 2x8s would be shorter. Bridging between joists are added when joists are more than 7 ft long, 2 times for 14 ft. Your 2x4 blocking between joists will work as bridging if none is there.
Adding a center support for the joists only works if you have a footing installed below frost level and covered, you wouldn't want to have the frost heave the new supports.



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Old 10-24-2011, 10:17 AM  
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Quote:
Originally Posted by nealtw
You didn't say how long the floor joists are. In new construction, we always use 2x10, and when the span is over 16ft the engineers often call for double floor joist or changing to 12" on center. 2x8s would be shorter. Bridging between joists are added when joists are more than 7 ft long, 2 times for 14 ft. Your 2x4 blocking between joists will work as bridging if none is there.
Adding a center support for the joists only works if you have a footing installed below frost level and covered, you wouldn't want to have the frost heave the new supports.
Thanks for the reply. The 2"x8" joists are 12' in length and spaced approx 18" apart. (Haven't measured, but looks to be about that wide.) The joists do have the little X boards in the middle of the joists, which are 1" by 4" slats. Thinking I can cut to fit and stagger the 2 by 4 boards in between the joists to help stiffen the floor. Just making sure I'm barking up the right tree before I do it. Thanks.
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Old 10-24-2011, 11:13 AM  
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I don't know but I would think 12 ft is about max for a 2x8. You maybe want to double up 2 or 3 of them just to see the diff. that makes.

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Old 10-24-2011, 11:43 AM  
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I've been reading up on bridging and it seems like it may help. Originally I was thinking I could stagger some 2x4s as bridging, but now thinking I might need to go 2x6's or even metal bracing.

In one of the articles I saw, it said that staggering the bridging - so you can nail directly into the board - is not recommended and that all boards should be in line. You direct nail one end and toenail the other. Does this sound right or will staggering work? Also, is it better to install the thin metal bridging of the wood? Final question: would it help to liquid nails in the wood bridging as well as nailing, or would that be a waste of time?

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Old 10-24-2011, 01:33 PM  
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The first reason for bridging is to stop the joists from rolling sideways when it warps and maintain spacing. I have seen solid blocking tried and I am not a beleiver. If you think about a stone arch with a keystone, it holds the arch in place, but when your floor bends down your arch is upside down. I would still go for double joists.

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Old 10-25-2011, 01:30 AM  
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If you're sure the joists are deflecting from being over-stressed, and not the beam (supported on piers) they tie into, a better solution than bridging would be to add flitch beams to the bottom of each joist in the "bouncing" area. Doing so is fairly easy, and can do wonders for increasing the section modulus of the members in question, making them stiffer and stronger.

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Old 10-25-2011, 04:57 AM  
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So, I've looked up the flitch beam. From what I can tell, it appears to be sistering in another joist with a steel plate in between, is this correct? If yes, where would one locally source these magic steel plates and what size would they need to be? Do they run the entire length of the beam?

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Old 10-25-2011, 04:59 AM  
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Wait, just read this again and saw you said to the bottom of each joist. Are you talking about underneath each beam? I'm missing something, but would like to know more please.

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Old 10-25-2011, 05:04 AM  
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Ok, I see where others have used plywood instead of steel for a flitch plate. Assuming I that's what you were talking about, but still interested in learning more please. Thank you.



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