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Unread 08-17-2007, 07:22 PM   #1
AllGoNoShow
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Oak Hardwood as subfloor?

In the old post WWI houses in the Northeast they use to attach the 3/4th thick strip oak hardwoods directly to the joists with no subfloor. Is there any problem with keeping this subfloor (then installing 1/2 CDX plywood over it and then Ditra)? I must imagine it is alot stronger then regular plywood.

Also, one more question- In my 2nd floor bathroom I have this oak subfloor. The joists are 14-15" on center (they prolly eye balled it when they build it) or so and are 2x6s spanning about 10 feet . The house was built in 1930 so the 2x6s are closer to the actual size of 2x6 and I've heard the wood they used back then is much better in terms of strength. The house is also made of plaster (I can't imagine it is much but plaster must provide some level of strength). I know the deflecto meter says no go, but does this take into account these other differences? I am 210 pounds and if I jump on the floor I don't feel any bounciness. Can I use a dial indicator to see if the floors will be able to support ceramic tile (what deflection would I be looking for max?). I may try to do it anyways (it would only be a $200 expierement) but i wanted to get your guys thoughts. Thanks.

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Unread 08-17-2007, 07:32 PM   #2
chuck stevenson
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Nick,

Is this the same project?

http://www.johnbridge.com/vbulletin/...ad.php?t=50843

If so, It is best to keep all questions in one thread so it is easier to follow the history.

I lived in late 40's home and the joist were 1-3/4 rather than today's nominal dimensions. They also bored and notched in ways that are not code today.
It is cheaper to secure your floor system now than do it and replace the tile later.
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Unread 08-17-2007, 08:31 PM   #3
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Nick,

Quote:
I must imagine it is alot stronger then regular plywood.
Nope.......
I usually replace the oak with ply...much stronger.... and use BCX or CCX Ply... Go heavy on the first layer and a little lighter on the second...

A good read..
http://johnbridge.com/vbulletin/showthread.php?t=8921
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Unread 08-17-2007, 08:40 PM   #4
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Chuck-Same House but different location (2nd floor bathroom)- I figured out what to do for the 1st floor kitchen from that thread. The problem is I can't cut the oak floor out all the way to the wall edges....the hardwoods are the subfloor so walls are on top of them.
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Unread 08-17-2007, 09:02 PM   #5
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Welcome, Nick. Please go to the UserCP above, find Edit Signature, and enter your first name there so it will appear in each post for us and we won't hafta search for it, eh?

While oak is a strong wood, it's not particularly rigid. In your situation I would leave it in place, though. I suggest you might wanna increase your top layer to 5/8ths ply, AC or BC or whatever is readily available.

And for sure you wanna go through there and add some decking screws in the existing boards. I recommend pre-drilling the boards. Old wood flooring was notoriously loose in the fastening.

Do you know what material those joists are? And do you know the actual unsupported span?
Quote:
I've heard the wood they used back then is much better in terms of strength.
Not always true and accurate.

Not very worthwhile to try to actually measure the joist deflection unless you are capable of loading the entire floor to at least 40 psf. If you can determine the wood specie, you may find the design deflection is within spec if those joists are a full 2 by 6 inches. Presuming the span to actually be ten feet.

And if that span is accurate, you'd want a deflection in the center of not more than a third of an inch, fully loaded. That's L (length in inches) divided by 360. But measuring it accurately and correctly ain't a simple proposition.

My opinion; worth price charged.
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Unread 08-19-2007, 02:19 PM   #6
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CX-Do you have anymore info (a how-to) on physically measuring joist deflection with a dial indicator? The 12x12 ceramic tiles I got are in boxes that are 50 pounds and I have enough to load more than half the floor at one time . Would this be okay (the load would be spanning 4-5 joists so i would be able to see if those deflect-then I can just move it to the other half and measure) How should I arrange the dial indicator (suspend it from the ceiling?) so as to measure it accurately.

Nick

Last edited by AllGoNoShow; 08-19-2007 at 02:26 PM.
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Unread 08-22-2007, 09:04 AM   #7
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I stumbled upon this thread: http://johnbridge.com/vbulletin/show...ing+deflection


Between Bob's engineering expertise and cx's post on the 2nd page, it was very helpful! I am going to do the 300lb test (I can stand on one foot in between the joists with a little weight added to me and easily reach that) and going to at least load half the floor to 50 lbs per sq. ft. and measure the deflection using a dail caliper on the 1st floor ceiling. I know it will not be a perfect way to measure-but if it is anywhere near the L/360 calculation I will not chance installation without beefing some things up. If it hardly measures any deflection-I figure I will be good to go. I will share the results to get your opinions.
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Unread 08-22-2007, 09:27 AM   #8
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Injineer Bob will be thrilled that you brought up that particular thread, Nick (long story). I'll bring it to his attention.

Good luck with your testing.
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