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leveling floor joists with 2x4s.....


zizanio's Avatar
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03-01-11, 06:39 AM   #1  
leveling floor joists with 2x4s.....

I will be installing a Bruce pre-finished wood flooring in my bedroom and I am thinking of leveling the 60 year old 3"x12" 16" on center 23' span joists so that I can install the 2 - 3/4 cdx sheet plywood subfloor on before the wood flooring goes in.
I was thinking of nailing/screwing 2x4s on to the sides of the 3x12s where needed for leveling purposes.
The floor is not sagging, but there is a small difference from joist to joist, I would say no more than 1/8 to 1/4" or 5/8" to 1" total in a 12 foot span.
I thought that nailing the 2x4s with 3" nails every 6"-10" would do.
Any comments come appreciated.


Last edited by zizanio; 03-01-11 at 08:49 AM.
 
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Pulpo's Avatar
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03-02-11, 06:59 AM   #2  
I don't think it's necessary. The plywood is flexible enough.

 
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03-03-11, 12:14 PM   #3  
Posted By: Pulpo I don't think it's necessary. The plywood is flexible enough.

Thanks Pulpo. The plywood is probably flexible enough you're right, but the money was burning a hole in my pocket so I went out and bought 40 2x4s and a box of nails and did it so that I wouldnt have to say "I should have" after I close it up.
Thanks again

 
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03-03-11, 02:58 PM   #4  
If you're sistering all those 2x4's to the existing joists, your underlayment seams will be offset and you need to bolt all the sisters to the existing joists. Nailing is not sufficient. Sorry to be the bearer of such news. Applying the plywood to the existing joists would have been fine, and if you needed, you could have floated the difference out.

 
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03-04-11, 03:33 AM   #5  
Afterthought. I would not use 2x4's for sisters, anyway. They must be of a dimension that will take the full weight of the floor, probably 2x10 in your case.

 
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03-05-11, 04:04 PM   #6  
Never heard that before, where did you get your information? A 10d (3") framing nail with 1-1/2" into the joist from the side will hold 120# shear.Attach the 2x4 every 2' nail spacing will give you 60# of shear, spaced 16" o.c., no worries at all.....depends on the joist spacing for the 40# per sq. ft. Common wire nails

Gary

 
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03-05-11, 04:40 PM   #7  
This is a bedroom so i believe this would work for you.Myself i would have used glue and screws.If you drive your spike the right way...on an angle..would help.Again.your bedroom, not subject to pianos or fridge..,etc. You may wanna double up on the spikes around the bed posts if ...ya know...lol..

 
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03-06-11, 05:59 AM   #8  
I saw this done on This Old House not too long ago. I believe Tom Silva used nails an construction adhesive. I think the most the 2x4 stuck above was about 3/4" in his situation.

This isn't my area of expertise, but I don't see much trouble with it. If for some reason it becomes problematic in the future, I think it wouldn't be too difficult to shore up. You can add screws, some lags and even put a larger board underneath the 2x4 and glue and bolt that to the old beam.

 
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03-06-11, 10:00 AM   #9  
My exact point, drooplug, why take a chance to having a failure when it can be done sufficiently to stay in the first place. Gary, you bring up a good reference, but I still don't like nails alone to hold up sistered boards that will carry the entire weight of what was a much wider and thicker board. The nails may be advertised as having a certain sheer strength, and I praise the Chinese for their intuitiveness, but not to hold up a critical part of a house. I think the OP will have to make a decision, and go with it. Hopefully not on the fact he already bought 40 2x4's.

 
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03-06-11, 12:11 PM   #10  
I also would never have used 2 X 4's,way to narrow and will tend to twist and cause squecks.
I also would never have used CDX as a subflooring. It's not even subfloor rated.
Subfloor rated would be 0 voids in the core. CDX is full of holes and should only be used for roof and wall sheathing.
Advantec T&G should have been used.

 
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03-06-11, 03:28 PM   #11  
The 2x4's are not spanning to hold up the load as a joist would. The 3x12's are carrying the load. Loads are transmitted straight down from above through the nails to the carrying joists. Span does not figure into the equation here, 2x4 or 2x6 wouldn't make a difference---- no span involved. It's the nail spacing that carries the load. And the 2x4 is not carrying "the entire floor" only the load above the nail.

Worried about twisting wood---- don't buy from the box stores.

Good point on the t&g though, or blocking is required; APA Blog for Professional Associates: Proper Orientation of Plywood Underlayment in Floor Systems

Gary

 
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03-15-11, 03:19 PM   #12  
Well guys, thanks for the comments. I decided to go with it as I originally posted. I must say, the job came out nice, I will post here if I see anything in time.

 
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