Reinforcing floor joists

Would appreciate suggestions on best way to reinforce floor joists under a wood floor (I want to support heavy loads, reduce vibration, make floor as rigid as possible).
Joists are 2x6 on 16" centers, lighter than average 2x8 construction and could use some help. House is 2 1/2 yrs old.
I've tried some jack posts supporting short extra 4x4 beams across the underside of several joists. But using posts (in a fairly new and still-settling house) creates high spots in the floor, requires contant readjustment. I would prefer strengthening the joist structure itself if possible.
Thanks in advance to anyone who cares to comment.
Art
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Could add parallel joists next to and attached to existing joists. Or block them with perpendicular blocks connecting joists. Where do they use 2x6" joists?

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Did you buy it new? Is there a structural warrantee? Seems pretty poor if you need to be fixing the structure this early.
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A house is 2 1/2 years old and used 2x6 for floor joists? What is the span? I would check building codes for your area, we use 2x6 for wall joists, and at least 2x8 or larger for floor joists. Most builders today use engineered beams for floor joists. Either way I would daughter additional 2x6 joists of the identical length and fasten securely to the original joists.
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You don't mention how heavy the load is, that you want to support. You also don't mention the length of the span for these joists. A 2X6 on 16 centers will span little more that 8 feet.
In addition, you don't mention what type of "heavy load" you will be carrying. If it's "normal living" stuff like a refridgerator or a piano, then you can probably add more 2X6's, so that there will be one every 8 inches. That will substantially increase the load bearing capacity.
http://southernpine.com/ That's a website that has charts for effective load bearing capacity of joists, based on grade, size, span, and other factors.
And you should also add bridges between the joists. These can be the old style diagonals, or solid bridging. Bridging spreads the load from each joist, to the ones that are near it, effectively strengthening the floor system.
Good luck.
snipped-for-privacy@sbcglobal.net (Art) wrote in message

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snipped-for-privacy@sbcglobal.net (Art) wrote in message

Knowing the span, type of wood, and end supports would help us think about the problem. Are the existing joists bowed? Are there pipes or ducts in the way?
Tom Baker
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Tom Baker wrote:

i have a similar question. one of my bedrooms floor will rattle a dresser if you walk heavy or jump a little. will cross bracing fix this. joist are 2x8 with a 16ft span, looks like old pine built in 1962. thanks
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I had a situation like this. Now when I buy furniture I check the hardware to see if small vibrations cause rattles. Too bad manufacturers just look at stuff to see if it is pretty.

if you walk heavy or jump a

like old pine built in 1962.

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<< Joists are 2x6 on 16" centers, lighter than average 2x8 construction and could use some help. House is 2 1/2 yrs old. >>
Don't waste time and money on this jerry-built dud, Start planning now to dump it and move as soon as you can. You may have to sell at a loss since disclosing faults is required in many locales. Just dry your tears and remember your tax accountant can make it less painful next year. Before you shop for a new house, start making a a check list now of things you want, things that are signs of shoddy wiorkmanship and present the list to your realtor when you're ready to go. This is no time for sentimentality. Good luck
Joe
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Hi again and thanks to all who replied. I'll have to choose between the "sister" joists attached lengthwise to the joists or the cross braces between joists--it's helpful to know either of these will strengthen the floor.
I appreciate those who worried I was cheated, but it's not the case. The house is otherwise strong and sound with a secure foundation. For most folks with normal furnishings it would be zero problem. My heavy items are storage cabinets, bookcases, media racks, and related stuff all in one large room or studio--that's the room that needs the reinforcement.
I forgot to mention another method I used successfully in a smaller upstairs room in another house, which was a layer of 3/4" plywood screwed and glued to the subfloor under the carpet. That worked really well. (Current house is single story, hence the jackposts.) I asked my carpet contractor to do the same in this house in that one room, but after the carpet was laid and all my furniture was in, I discovered he had used 5/8" chipboard instead of good 3/4" ply. This is softer and doesn't add enough rigidity. I could always empty the room & try again, but maybe doing the joists will be simpler.
Art
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