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Old 04-04-2011, 03:10 PM   #1
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Beam for bouncy floors


I have 2x8 floor joists that are on 16" centers and spanning 15'4" each. It is an old farm house and the floors do bounce. My calculator shows a L/200 range on those specs. If I change the span to 7.5' range, this can get my specs to an L/700+ range.. a HUGE difference for us.. I will have about 4 floors that i will have to do this at.

I would like a simple plan for a beam under these floors and my thoughts were to -add concrete footers for columns/piers
-use 4x4 columns, or built up CMU pier, or crawlspace columns...
-figure out the size of the beam necessary... need help here! I think either a built up 2x6 (2-3 courses???) or can I use 4x4 materials??? I have to keep the material size realistic since I have limited crawlspace access.

Can anyone please point me in a direction that I can calculate the correct beam?

Thanks

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Old 04-04-2011, 05:28 PM   #2
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Beam for bouncy floors


Structural engineer.
Ron

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Old 04-04-2011, 05:40 PM   #3
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Beam for bouncy floors


Go straight to the Lumberyard.
Wave to the Orange people as you go by Home Depot.

The lumberyard can probably spec you out an LVL or other laminated configurations that will meet your requirements.
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Old 04-04-2011, 06:02 PM   #4
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Quote:
Originally Posted by bnentrup View Post
I will have about 4 floors that i will have to do this at.
When you say "4 floors" do you mean four rooms or four floors in height (meaning first floor, second floor, etc)?
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Old 04-04-2011, 06:04 PM   #5
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Beam for bouncy floors


the size of the beam depends on how much concrete you want to pour.
3 ply 2x10 10-12' or so, 3 ply 2x8 6-8' or so
google, beam, lvl, psl spans see what you get. lvl and psl charts don't usually don't go under 20-24'.

Last edited by craig4; 04-04-2011 at 06:22 PM.
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Old 04-04-2011, 06:39 PM   #6
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have you thought about sistering the existing joists?
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Old 04-04-2011, 11:06 PM   #7
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Thanks all for the response; looks like I have created a pessimist with Ron in another posting... going straight for the 'hire it out and support skilled trade' -- Ron, I have been in a skilled trade for many years now; I just won't tell you which trade to keep the suspense and drama up (that is a joke).

However, this is the DIY forum... therefore, I appreciate the feedback from the others.

YES, I have considered sistering the joists. The most feasible would be using plywood sections that can easily fit in the crawlspace and glue/screw. I could sister on each side and possible get a much more substantial joist this way. HOWEVER, I have read from others that this may not get as much bang for the buck as a girder. How can I calculate the deflection rate with plywood reinforced sister'd joists?

Therefore, I look'd first at the girder. I could dig&concrete 3 holes for the 16' span, meaning a max span of 8' between supports. That equates to a 3 ply 2x8??

Between the 2-choices: plywood sister joists 3/4" ply on each side of the joist screwed/glued -- and possible adding banding or some blocking of sorts??? -- vs built up girder or beam?
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Old 04-05-2011, 08:04 AM   #8
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What I think I hear you're saying by using the plywood is called scabbing, which is different than sistering. Sistering constitutes the same span as the existing joist - 15' 4" and I would use 2x8's for this purpose.

The thought was that it would be easier to drag some lumber in than the dirt out and then the concrete in - probably bucket by bucket.

Not knowing the specifics about the working space, access and floor load requirements the suggestion was given from the perspective of limited working space and get the bounce out of the floor. Sistered 2x8's would do this given normal housing load requirements.
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Old 04-05-2011, 10:21 AM   #9
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Beam for bouncy floors


It sounds like he is in a very limited work space though. He might be better off with a girt like he said originally.
This is a pretty standard kind of fix for the older homes in my area, 4x6 girt with posts and piers about every 6 feet or so, all depending on the details though. Like load transfer if any, or is it merely stiffening the floor. Lots of strategies that would be appropriate for a DIYer.

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Old 04-05-2011, 12:50 PM   #10
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My joists were 2x8 on 24" centers, 15-6 span. It was like a trampoline.

I used PT 2x6 and metal (Simpson) ties to connect the 2x6 to the beams. Then I pushed concrete blocks under the 2x6 and shimmed as necessary.

It's been that way for 10 years now.
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Old 04-05-2011, 01:00 PM   #11
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Beam for bouncy floors


pyper, I am very interested due to the simplicity as it sounds, but a bit confused:

sounds like you made a beam with 2x6 materials?? and used concrete blocks (no footer) to support.

I suppose the only issue I could forsee is having to continually shim the beam support as the ground settles.

if you could explain further I would greatly appreciate it.
thanks!
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Old 04-05-2011, 02:09 PM   #12
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Beam for bouncy floors


There are two ways to do this correctly, sister the joists or dig footings and add a beam mid-span. Anything else will be called out by the inspector when it's time to sell and you'll have to do it anyway.

Why are you opposed to having an engineer spec a beam for you? Even if it's the guys at the LLY. Most will do it for free.
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Old 04-05-2011, 09:44 PM   #13
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Table #3 and 4; http://www.lancova.com/deckinfo.pdf

Gary

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