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Old 01-22-2010, 01:38 PM  
Todd-Beaulieu
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Default Eliminate bounce on old floors

Hello,

I have a super old home in a 4-corner layout. When we walk, there's quite a bit of bounce. You should see it when we play the Wii!

Each quadrant's span is about 14' - a few inches over. The joists are 2x8 (true size), 18" O.C. One end is nailed to a beam that rests on the foundation wall, the other is notched into the inside beams (center of the house). There's no ceiling down there and very little "cross bracing" - one in the center of each span. Oh, and there's no plywood subfloor. This house was built long before plywood was invented. I believe there are simply two layers of wood plan floor ... the "sub floor" layer and then the soft wood flooring above. Spilled drinks quickly make their way to the basement!

As a test, I added a 4x6 beam under the living room with two jacking stands. I only applied a little pressure - wasn't trying to jack it up, just support it. It's now rock solid.

My initial thought is that it would be preferable to NOT use adjustable stands, but rather some form of improved cross bracing or sistering LVL beams to the existing.

I read about Luxor's IBS2000, which looks really effective.

Does anyone have any suggestions?

Thank you!



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Old 01-22-2010, 03:34 PM  
Wuzzat?
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Quote:
Originally Posted by Todd-Beaulieu View Post
When we walk, there's quite a bit of bounce.

Each quadrant's span is about 14' - a few inches over. The joists are 2x8 (true size), 18" O.C.

As a test, I added a 4x6 beam under the living room with two jacking stands. I only applied a little pressure - wasn't trying to jack it up, just support it. It's now rock solid.
Borrow a book, through interlibrary loan if necessary, on "Lumber Engineering." There are probably several on this subject.

It should confirm what you are seeing and what is necessary to get the center-span-deflection down to acceptable levels.
http://www.google.com/search?client=safari&rls=en&q=l+360+deflection+criteria&ie=UTF-8&oe=UTF-8
Or look at the latest version of the International Residential Code.


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Old 01-22-2010, 04:47 PM  
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This has been discussed here in the past - do a search.

The upshot is that you can sister on dimensional lumber in the center of the span and add blocking or cross braces to adjacent joists or do something fancy like add material to the bottom of the beam to increase its second moment of inertia.

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Old 01-22-2010, 07:08 PM  
Wuzzat?
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This site also comes in handy, sometimes
Stress and Deflections in Beams

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Old 01-26-2010, 04:27 PM  
Todd-Beaulieu
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Thanks guys. I actually had searched the forum before posting. The first thing of interest was on the fourth page. The internet's great for info ... if you can find it! And so many people post with generic subjects, you can't tell what's being discussed.

I'll spend some more time going through the previous posts, as well as the provided links. Thank you.

I just used a level laser to measure the height difference between the outside wall in one room, with that of the inside wall (distance from floor to projected line). Over 2" of difference! Yikes. I have a lot of research to do, that's for sure, in trying to figure out a course of action, including the possibility of no action, at least for the sag.



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