Underlayment before hardwood


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Old 03-20-15, 10:24 AM
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Underlayment before hardwood

Hello folks,

I need to install an underlayment over my subfloor before installing hardwood, so that my wood ends up being flush with the tile which it needs to meet up with. I am now exploring what material and fasteners I am going to need for this.

I am going to need to add about 1/2" to my 5/8" plywood subfloor. Can I use OSB, or does it have to be plywood? OSB would certainly be cost effective, but if it's not the right way to do it, I don't want it. I understand houses are built with OSB subfloors now, so this is why I ask. If it makes any difference, I intend to lay felt paper down before installing the wood.

Also, would nailing the OSB (or plywood) down with 2" ring shank nails going to suffice, or should it be screwed down, like when installing ceramic?

Thank you!
Nic
 
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Old 03-20-15, 01:24 PM
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I worked for a floor guy & we never used felt paper or any other underlayment between the plywood & the finished floor. I would go with screws instead of nails. I'm not sure about OSB.
 
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Old 03-20-15, 02:05 PM
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What does the flooring manufacturer say about underlayment?

Do you intend to nail down the hardwood?
 
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Old 03-20-15, 02:05 PM
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OSB is fine. Ring shanked nails or screws, but NOT into the joists below. Intentionally miss the joists and attach the second layer only to the layer below between joist bays. NO glue. No felt paper between layers of subflooring. We use felt paper under the hardwood. It helps to keep down inherent squeaking of the floor and gives a vapor barrier as well.
 
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Old 03-20-15, 05:11 PM
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My rule is if you are going to walk on it, you screw it. Ring shank nails hold the best in the nail department, but nothing beats the holding power of screws. When it comes to floors or stairs, anything you can do to reduce the chance of a squeak, you do it.

I would reattach all your existing plywood with 2 1/2" deck screws 8" on center into the joists, paying attention to remove any nails that already have worked their way loose. Once done, walk over the floor for a while to make sure there are no existing squeaks. Now is your only chance to eliminate them. Next attach your second layer of OSB (not aspenite) with 2" deck screws 6" on center over the entire sheet.
 
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Old 03-20-15, 05:40 PM
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I would have said almost exactly the same thing as Keith, but I'd probably be using 1 5/8" deck screws.
 
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Old 03-20-15, 09:07 PM
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For hardwood nail down, you need minimum 3/4" OSB or minimum 5/8" plywood. This is for shear holding power of the cleats or staples. OSB can "blow out" on the opposite side of where the nail is driven and therefore requires a thicker material.

so that my wood ends up being flush with the tile which it needs to meet up with
This is the worst reason to adjust standard best practices. The floor will need basic minimums to be structurally sound. It doesn't care and is not dependent of the adjacent flooring and that should have no bearing on how you install the hardwood. If thicker to be a quality install then so be it, install a transition strip.
 
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Old 03-21-15, 04:40 AM
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I have never had a bad threshold problem meeting 3/4" wood flooring to tile. You have 1/4" cbu, thinset and tile which will just about make 3/4" and a smooth transition. Otherwise, as Z says, it is just the nature of the beast and you have to deal with it. Don't compromise structure for aesthetics.

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Old 03-23-15, 06:55 AM
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Thanks for all your responses guys!

stickshift - yes I intend to nail down the hardwood.

chandler - I have no intention of compromising structure for aesthetics. If it's not even, I will use a transition strip. No big deal - they are everywhere.

-czizzi says I need at least 5/8 ply... Is this on top of the 5/8 ply I already have as a subfloor? I was under the impression that hardwood doesn't need the same decoupling as tile does when it comes to underlayment, as I have seen people install hardwood directly to subfloor on many occasions (then again, I'm starting to learn that apparently thing's aren't done the "right" way often).

Also, you guys keep talking about deck screws. Can't I just use regular flooring screws like the ones I use to attach plywood before tiling?

Thanks again
Nic
 
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Old 03-23-15, 07:00 AM
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Can't I just use regular flooring screws like the ones I use to attach plywood before tiling?
Most of us use decking screws because they are readily available. Do not use drywall screws! as they are brittle and prone to break
 
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Old 03-23-15, 07:46 AM
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Do not use drywall screws!
I would never !
 
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Old 03-23-15, 10:58 AM
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I don't consider plywood structural in the 3/8" to 1/2" range, too much flex and does nothing to stabilize the floor. You plan on adding to make your height transition. However, 1/2" added is not what I would do. If it was reversed, with 1/2" down first and you wanted to add 5/8" on top, I would be good with that. Again, it has to do with the holding power of the main portion of the shank of the cleat used to hold the flooring. Your fat part of the shank will hold fast to the top layer but do nothing as far as hold in the lower layer. Movement will eventually work the narrow front of the cleat loose and it will be useless. Enter a squeaky floor. So yes, if you are adding, I would recommend the 5/8" minimum for max. grab on the cleat.

As far as OSB, 3/4" minimum regardless of what is underneath. 1/2" OSB is rated for sheathing not for subfloor installation.
 
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Old 03-23-15, 11:42 AM
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Makes perfect sense boss, 5/8" it is
thanks!
Nic
 
 

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