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Fixing bouncy floors

absolutbmc's Avatar

Join Date: Oct 2017
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01-13-18, 07:48 PM   #1 (permalink)  
Fixing bouncy floors

Hi all, looking for some help. My dining room has a lot of bouncy to it that I am trying to fix. The room is probably 12 X 10. There isn't a beam underneath it. The joists are 12 X 8 and there is a row of braces down the middle. I don't think I will be able to sister the joists. I've heard adding more X braces will help. But, I've also heard block helps also. Do people have experience with either option? Preferences? If I went with X braces, what size wood should I use? 13?

Thank you

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XSleeper's Avatar
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01-13-18, 07:52 PM   #2 (permalink)  
Blocking and bracing will not add any perceptible strength. You need a beam under the joists to split their span in half.

Marq1's Avatar

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01-13-18, 11:48 PM   #3 (permalink)  
Over the past couple of houses I've added multipal laminate beams with adjustable posts to select rooms to stiffen the floor. It works great and is not terrible expensive.

And no you dont have to worry about a footing since you are just removing the movement of the floor, it's not load bearing.

Gunguy45's Avatar
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01-14-18, 02:08 AM   #4 (permalink)  
Well, according to multiple sources...metal bracing is cheap and might be a quick fix, but verify what you have is not loose. They tend to come loose due to expansion and contraction, so first add fasteners to tighten them up if needed. Adding 2 more rows would be an option.

After that, solid blocking directly in line (not staggered) would be better than the metal. They have to be a very tight fit, any slop defeats the purpose.

There was also mention of using a metal strap looping down from one end, bent around the bottom middle and looping up to the other end...sort of like the tension cables on one of those single center pole antenna's or a cable stay bridge? It transfers the load from the middle to the ends.

Another way of sistering would be to use 3/4" plywood glued (construction adhesive) and fastened to the sides of the joists. It would probably be easier to maneuver into position and if you staggered the joints should be pretty effective. Ever try to bend a strip of plywood across the flat?

And of course there's the tried and true sistering with dimensional lumber or LVL.

Almost all of these would require jacking the floor slightly to relieve stress.

And you need to make sure your existing joists aren't bowed, just bouncy.

There are numerous reputable sources that can give more in depth info. Just do a search for "Does adding blocking stiffen a bouncy floor?". I know it's exactly what you're asking here, but they can go more in depth with diagrams, pictures, etc...that's what they get paid to do.

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