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jdelisle 01-02-2008 03:06 PM

Strengthening a bouncy floor
I have a bouncy floor (too much deflection), and want to strengthen it prior to installing hardwood and tile.

The joists/beams are accessible, and are 16" OC, 15 foot span from beam to beam.

I believe my options are:
1 - add another beam towards the center of the existing joists
2 - add solid blocking or cross bracing between joists
3 - sister the joists

Option 1 seems to be the easiest, since I wouldn't have to modify any electrical or plumbing to do it.

Anyone have any suggestions/experience with a situation like this? I'm fine doing the work, and want to do it once and do it right.

Rehabber 01-02-2008 03:20 PM

What size are the existing joists?

Bondo 01-02-2008 03:49 PM

Ayuh,........ #1 sounds like the Right Plan,........

#2 would require a Ton of blocking,+ I Doubt #3 would do much Good at All.......

Cole 01-02-2008 03:53 PM


Originally Posted by Rehabber (Post 84843)
What size are the existing joists?

I agree, we need more information!

jdelisle 01-02-2008 04:02 PM

Sorry forgot to mention - the existing joists are 2x8 spruce, 15 foot span, 16" OC.

I realize the existing joists may not meet typical building code, and plan to talk to the builder about it.. unfortunately the home is 20+ yrs old.

I believe I may be wrong re the additional beam being easiest - it seems teleposts require a minimum of a 30"x30"x30" pad, which mean digging up the basement.. uggh.

So, lets forget option 1.

WMitch6 01-02-2008 04:20 PM

I wouldn't give up on option 1 yet. Are you sure your area needs a footer requireing nearly a yard of concrete? I poured reinforced footers for lolly posts in my basement and they only needed to be 2' X 2' X 12".

Sistering the joists will probably work but that's not always as easy as it seems. Electrical is usually easy enough to move but plumbing can be a problem.

Bondo - I'm curious why you think sistering the joists wouldn't work. I'm not a builder, but I've done this a couple of times to stiffen a floor so that it would carry stone tiles.

Rehabber 01-02-2008 04:36 PM

Sistering the joists will make your floor feel pretty solid, but not stiff enough for ceramic tile. Adding a cross beam with a support will get you a floor stiff enough for tile or stone

Bondo 01-02-2008 04:37 PM


The Quickest,+ Usually the Easiest way to tighten or straighten a span in my mind,.......
Is to Shorten it.......

How many 16', 2X8s is it going to take to Sister the existing joists,..??...

Turn'em the Other way,+ you need 3 or 4.........


which mean digging up the basement..
Just What is this Basement Space we've got to work with,..??...

You're trying to Tighten a Floor,....... Not Jack the Whole House........
No Way you need a couple Yards of Concrete........

jdelisle 01-02-2008 05:40 PM

I talked to a guy from the city home inspection office, he suggested the 30x30x30 footings. Seemed awful large to me too, but he says because it's a split-level (two story) home and the basement pad isn't load-bearing thickness, it would need that footing under the teleposts.

I do plan porcelain tile above this in one room, by the way. The rest will be hardwood.

Thanks for all the advice so far.

Rehabber 01-02-2008 05:57 PM

Your current deflection calculates at L166. If you sister the joists it will bring you to L332, still not enough for ceramic tile which requires a minimum of L360. If you can add a cross beam in the middle (with supports) you can get this all the way up to L946. Or maybe sister with 2x10s?, which would get you above L360

jdelisle 01-02-2008 06:23 PM


Originally Posted by Rehabber (Post 84907)
Or maybe sister with 2x10s?, which would get you above L360

If I sister with 2x10's, I'll need to notch the ends a little so they'd fit on the current beams beside the existing 2x8's. Think that would be OK?

Rehabber 01-02-2008 07:21 PM

Yes, that will work

gallen12 10-30-2012 05:42 PM

Give me a call. I am sure I can help. WWW.LUXORCORP.COM

GBrackins 10-30-2012 05:47 PM


sure they got it worked out by now, that was almost 5 years ago

I missed the dates sometimes myself :laughing:

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