# Firm up floor by bracing joists?



## JSDNJ (Jan 2, 2017)

My home was built in the 20s. Walking from the kitchen to the living room is a bouncy and furniture rattling experience. Needless to say I'd like to firm up the floor. I have access to the joists in the basement. It has some cross bracing but I wonder if adding blocking would help? Or more cross bracing?

The area in question is in between the cross bracing and the header.


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## Daniel Holzman (Mar 10, 2009)

Step 1 is to accurately measure the depth and width of all the structural elements (joists, beams, posts). Then measure the free span of the joists, looks like it might be 20 feet or more from the photos. Then you can calculate the deflection index, go to the John Bridge website and use the deflection tool (no charge). http://www.johnbridge.com/vbulletin/deflecto.pl

My guess is your joists are overspanned. No amount of bridging or blocking will cure bouncy floor syndrome due to overspanned joists, you either need to sister the joists, replace the joists with deeper joists, or shorten the span using an intermediate beam.


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## stick\shift (Mar 23, 2015)

No calculations done but my first thought looking at the pictures was your joists were over-spanned.


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## Bondo (Dec 8, 2007)

Ayuh,.... The quick, 'n easy answer is,.....
Another pole in the middle of the bouncy spot, with a doubled 2x6 on top of the pole, perpendicular to the floor joists,....


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## joecaption (Nov 30, 2011)

Looks like every old home I've worked on.
If you do decide to add another beam to split up the span you also need to cut out the floor and pore new footings for the post
Depending on where you live and soil conditions a typical footing is 24 X 24 X 8" thick.
If it was mine I'd also add joist hangers.


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## lenaitch (Feb 10, 2014)

joecaption said:


> If it was mine I'd also add joist hangers.


Great suggestion but it looks like the joists might be notched over a 2x4 (difficult to tell for sure from photo).


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## JSDNJ (Jan 2, 2017)

joecaption said:


> Looks like every old home I've worked on.
> If you do decide to add another beam to split up the span you also need to cut out the floor and pore new footings for the post
> Depending on where you live and soil conditions a typical footing is 24 X 24 X 8" thick.
> If it was mine I'd also add joist hangers.


Yea, that's more than I am going to want to do at this time. It's also an awkward place to put another beam. (Though I suppose I could consider that in the future)


Some more info:

From the 'header' on top of the foundation to the center of the 'header' in the picture, the joist spans about 169''. The joists themselves are 9 1/2'' deep and 1 3/4'' wide. 

There are 3 beams placed along the header down the center of the basement, (1 is visible in the picture) and another beam is at one corner of the staircase (other side is just a 2x4)

See picture below:

I'll have to call a contractor, but does another beam seem necessary? I have to decide how much $ is worth a little rattling when I walk.


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## MonsieurBon (Feb 14, 2016)

I've heard this strap technique can be useful for making overspanned joists a little less deflect-y.

Basically using steel strap in tension from bearing end to bearing end, nailed often, and wrapping/crossing under the midpoint.


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## Gary in WA (Mar 11, 2009)

---------Welcome to the forums!----------------------------------

Your 14' span MAY be fine, depending on the species/grade/on center spacing/load, look for an ink stamp on the side to check the charts on-line, eg- old IBC; http://www.ce.udel.edu/courses/CIEG407/Class_17/Wood%20Chapter%2023%20-%20IBC.pdf Scroll about 1/2 down....

There are many ways to retro stiffness; http://www.finehomebuilding.com/pdf/021184090.pdf

Another, adding a 2x to bottoms;--* both pages*- http://www.diychatroom.com/f19/floor-bounce-joist-sistering-34846/ 

Gary


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## JSDNJ (Jan 2, 2017)

So I am getting ready to tackle this project. Some more info:

The joists are 2x10s 16'' on center and a 14' span.

I was planning on sistering the joists, but was thinking maybe I could try some bridging first.

Was thinking something like this:

http://www.homedepot.com/p/Simpson-...gclid=CJG6q4Kh69ICFUZLDQodQnwMdg&gclsrc=aw.ds

Will this work for joists already in place as opposed to new construction?

Now if the bridging is no good and I need to sister, How do I attach the joists at the ends? On one end, I can notch the joist to match the current one and lay on the 2x3 pictured.










But on the other end the joists are on the 2x4 sill, and I wont have access to rest the sistered joist onto it because of the other 2x10 in between.










Any thoughts on this and how to firm up my floor would be greatly appreciated.


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## Daniel Holzman (Mar 10, 2009)

2x10 joists 14 foot span 16 inches on center for a room with 40 psf live load and 10 psf dead load have an l/d (stiffness ratio) of more than 400, assuming E (modulus of elasticity) =1.5 million, pretty typical for old lumber. The joists are also strong enough in bending to resist the loads, but you already know that, the floor is still there. So the conclusion is that sistering the joists, while always a fun project, is not likely to improve the bounce.

Your bounce may be caused by something else, maybe improper installation of the subfloor, or inadequate subfloor stiffness (my old house had 3/4 diagonal subfloor with no plywood). You should check out the entire floor installation before you sister the joists only to find out that does not resolve the issue. You may want to bring in a flooring expert to help you assess the source of the problem.


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## JSDNJ (Jan 2, 2017)

Daniel Holzman said:


> 2x10 joists 14 foot span 16 inches on center for a room with 40 psf live load and 10 psf dead load have an l/d (stiffness ratio) of more than 400, assuming E (modulus of elasticity) =1.5 million, pretty typical for old lumber. The joists are also strong enough in bending to resist the loads, but you already know that, the floor is still there. So the conclusion is that sistering the joists, while always a fun project, is not likely to improve the bounce.
> 
> Your bounce may be caused by something else, maybe improper installation of the subfloor, or inadequate subfloor stiffness (my old house had 3/4 diagonal subfloor with no plywood). You should check out the entire floor installation before you sister the joists only to find out that does not resolve the issue. You may want to bring in a flooring expert to help you assess the source of the problem.


I am no expert, but to me it doesn't 'feel' like the subfloor is the issue, it feels 'bouncier' than that, if that makes sense.

In any case, I have hardwood throughout, so doing anything above the joists is not something that is going to happen in the foreseeable future. Some of the existing bridging is a little loose, and they did drill some holes to run BX through the joists over the years. 

Perhaps attempting with the metal bridging would be a cheap first try?


Edit:

I cant speak for the whole house, but the area I CAN see (going into the basement) shows me a cross section of the subfloor, where I have the diagonal subfloor but no plywood (just the hardwood on top)


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## Gary in WA (Mar 11, 2009)

Simply adding a 1x4 perpendicular to the joist bottoms will increase stiffness three-fold from just cross bridging (with full bearing on the bottoms, not 1/2 bearing as your cross appears)--- from 9% to 25% past no bridging; http://support.sbcindustry.com/Archive/2004/jun/Paper_278.pdf?PHPSESSID=ju29kfh90oviu5o371pv47cgf3

Gary
PS. Add the new rows of metal X-braces with new 1x4.... reducing the spans of bridging.


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## JSDNJ (Jan 2, 2017)

So, I sistered every other joist and bolted them with through bolts. It helped a bit but not much. 

What to try now? Sister the others too? Something else?


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## JSDNJ (Jan 2, 2017)

Gary in WA said:


> Simply adding a 1x4 perpendicular to the joist bottoms will increase stiffness three-fold from just cross bridging (with full bearing on the bottoms, not 1/2 bearing as your cross appears)--- from 9% to 25% past no bridging; http://support.sbcindustry.com/Archive/2004/jun/Paper_278.pdf?PHPSESSID=ju29kfh90oviu5o371pv47cgf3
> 
> Gary
> PS. Add the new rows of metal X-braces with new 1x4.... reducing the spans of bridging.


Hey Gary can you clarify what you mean by full bearing vs 1/2 bearing?


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## carpdad (Oct 11, 2010)

Cross braces look ok. Most of them have full contact with joists. I'd suspect the bounce and rattle you feel is stuff in the room where you feel the bounce. Doors, cabinet doors, dishes, trinkets on display, etc, can add to the noise. It is odd that you feel not much improvement after all that work. Try propping up 2x4 on the main girder as well as middle of the joists. Make them tight to the floor. If bounce goes away (this depends on your subjective feel because depending on situation, this bouncy feeling will be there always unless you over build), then you can pin point to some problems. 2x10x14' joists should not be "bouncy".


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## JSDNJ (Jan 2, 2017)

carpdad said:


> Cross braces look ok. Most of them have full contact with joists. I'd suspect the bounce and rattle you feel is stuff in the room where you feel the bounce. Doors, cabinet doors, dishes, trinkets on display, etc, can add to the noise. It is odd that you feel not much improvement after all that work. Try propping up 2x4 on the main girder as well as middle of the joists. Make them tight to the floor. If bounce goes away (this depends on your subjective feel because depending on situation, this bouncy feeling will be there always unless you over build), then you can pin point to some problems. 2x10x14' joists should not be "bouncy".


Some of the cross bracing you see in the picture is gone now since sistering. 

I can feel the bounce if I’m sitting on the couch and someone walks by.


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## Nealtw (Jun 22, 2017)

JSDNJ said:


> Some of the cross bracing you see in the picture is gone now since sistering.
> 
> I can feel the bounce if I’m sitting on the couch and someone walks by.


Replace the ones you pulled with solid blocking,


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