Leveling subfloor - 1/4 ply?

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Old 04-30-15, 03:12 PM
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Leveling subfloor - 1/4 ply?

Is there any problem using 1/4" ply to build up an existing plank wood subfloor? The planks are 7-1/2"w x 3/4" set at 45 degrees diagonal to the joists. I want to use 1/4" to make the new floor level with flooring in the adjacent room i.e. want a level transition.

Will the thin 1/4" ply create any unforeseen issues, even though I'm relying on it only for leveling? If its Kosher, then how would you attach the ply? 1" fully threaded screws every 6" on the edge and 8-10" in the field?

btw:

* the new hardwood (going over the planks+1/4 ply) is 3/4" solid hickory.

* after reading other posts on the subject of sub-floors, I've decided NOT to use glue between the ply and planks, and NOT to nail the new ply through to the joists.

Thanks for any help!
 
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Old 04-30-15, 03:39 PM
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Welcome to the forums. I know you want a perfect union of the flooring, but 1/4" is not approved as a subfloor for hardwood. I would go ahead and install 1/2" subfloor grade plywood, using 2" decking screws, as you observed without glue and not hitting the joists (glad you read up on it

I also know you have set your sights on the 3/4" flooring. Could you back off to 5/8" hickory, change the foot of the nailer and proceed from there?
 
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Old 04-30-15, 04:44 PM
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Keep in mind that Larry's recommendation of 1/2" does not pertain to OSB panels. OSB minimum requirements for nail down is 3/4". And the 1/2" is allowed only because you have another subfloor underneath that, otherwise it is 5/8" with ply. This is for the benefit of others reading down the road. OSB requirements have to do with holding power of the cleat vs thickness of the subfloor.
 
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Old 04-30-15, 07:58 PM
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Thanks, looks like I'll just go directly on the planks and live with the offset. I already own the 3/4" and, after experimenting with a thicker under-layment material, the remaining 1/8" offset is tolerable.

Nevertheless, what are the risks of breaking the rules and using 1/4" ply over planks? Obviously 1/4 would be worthless on its own but why isn't it allowed over an existing subfloor?
 
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Old 05-01-15, 03:53 AM
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experimenting with a thicker under-layment material
What underlayment material are you speaking of? Usually 15# builder' felt is all that is needed under full thickness cleat/staple down flooring. I won't advocate using the 1/4" as it is not of an underlayment quality, and may contain voids within the plies. I understand your quandary. The problem you may have is the flooring may not fasten properly to the diagonal subflooring. Quite a bit of voids between boards in many instance, and not a solid strata, which is required for hardwood flooring.
 
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Old 05-02-15, 07:25 PM
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The underlayment I referred to is the Bellawood Premium Underlayment from Lumber Liquidators:

Premium Underlayment 100 Sq Ft - BELLAWOOD | Lumber Liquidators
 
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Old 05-03-15, 04:46 AM
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The underlayment would be fine, as the dealer recommends it. It is totally overkill for naildown flooring and I would not waste money on it. 15# roofer's felt is the common underlayment. You won't be seeing any appreciable "cushioning" from using the thick underlayment as your flooring will be drawn tight to the subflooring when you staple/cleat it down.
 
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