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Discussion Starter #1
So we will be installing 5-in wide hardwood flooring but will be putting it over 1/4-in plywood as our sub floor is not exactly level. A few questions.
is it best to screw the plywood to the subfloor or nail it? I need best practices for spacing that are screws or nails? How can I make sure I get the plywood level in areas where the dips? What's used, a shim? Thanks . By the way is there any way to donate here I'm extremely grateful for all the responses since I've joined this forum? Attached to some pics of my first and second floor subfloor.
 

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retired framer
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!/4" plywood will conform quickly to the shape of the floor below it.

I would go all the way up to 5/8 and you would have a better chance of the screws pulling the boards up under the plywood.

I would use construction screws that are just longer than the plywood and subfloor total thickness, 6" OC around the edges 8" OC in the field.
 

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Discussion Starter #3
!/4" plywood will conform quickly to the shape of the floor below it.

I would go all the way up to 5/8 and you would have a better chance of the screws pulling the boards up under the plywood.

I would use construction screws that are just longer than the plywood and subfloor total thickness, 6" OC around the edges 8" OC in the field.
Great point but now it'll be raised up too high. I think it'll cause issues were out sliding doors are. Sh&$😁☺
 

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Discussion Starter #4
There has to be some other way. It's actually only dipped in one area that's about 4'x4'. He said the plywood is mainly because we will be gluing the hardwood floor
 

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Hammered Thumb
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I'll ditto what Neal said, 1/4" will follow dips. Make sure to differentiate between "just plywood" and "underlayment." For a glue-down, either will need to be APA rated (meaning sanded and filled for "B" faced plywood or proprietary products like IntegraPly).

If you are gluing the engineered wood and have just small areas of waviness, you can use self-leveller. Do you want to glue it as opposed to nailing? If it is nailed, you can get away with filling shallow dips with felt paper. Also, can you explain how a sliding door would be affected by an underlayment thickness? Usually you have the track which requires a step over anyway, the floor butts up to it.
 

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I can give you the following tips for leveling :-

Place strips of plywood across the floor to fill deeper slopes, increasing the thickness of the plywood at regular intervals to correct the slope. For example, fill a 1-inch slope across 8 feet by putting a 12-inch strip of 3/8-inch plywood at the point where the slope is that deep.
 

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Discussion Starter #8
I'll ditto what Neal said, 1/4" will follow dips. Make sure to differentiate between "just plywood" and "underlayment." For a glue-down, either will need to be APA rated (meaning sanded and filled for "B" faced plywood or proprietary products like IntegraPly).

If you are gluing the engineered wood and have just small areas of waviness, you can use self-leveller. Do you want to glue it as opposed to nailing? If it is nailed, you can get away with filling shallow dips with felt paper. Also, can you explain how a sliding door would be affected by an underlayment thickness? Usually you have the track which requires a step over anyway, the floor butts up to it.
Don't you glue any hardwood 5" or wider?
 

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Discussion Starter #11
I'll ditto what Neal said, 1/4" will follow dips. Make sure to differentiate between "just plywood" and "underlayment." For a glue-down, either will need to be APA rated (meaning sanded and filled for "B" faced plywood or proprietary products like IntegraPly).

If you are gluing the engineered wood and have just small areas of waviness, you can use self-leveller. Do you want to glue it as opposed to nailing? If it is nailed, you can get away with filling shallow dips with felt paper. Also, can you explain how a sliding door would be affected by an underlayment thickness? Usually you have the track which requires a step over anyway, the floor butts up to it.
Im just worried about raising it to high and have it interfere with bottom of interior doors, front door and sliding door. Just with the sliding door your right...it would have to be raised up pretty high to be above the track.
 

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Discussion Starter #12
Can my hardwood floor go right on top of my sub floor shown on pics? Again it's going to be wide plank...about 5". The 1st floor is a little different sub floor than the 2nd floor as you can see. Thank you .
 

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Glue assist means you nail the flooring but put a bead of glue perpendicular every _"o.c. per manuf instructions.

Any flooring you put down you might have to cut door jambs and bottom of door slabs. Exterior doors should be fine with the slider track or threshold raised above the subfloor.

What is the flooring you are putting down? Engineered (12mm-15mm) or solid hardwood (3/4")?

Based on subfloor being not that unlevel as you said in post #4:
- If you are nailing either, you can put them right on top the subfloor. Any high spots can be sanded and low spots shimmed with the felt paper. Note if the existing subfloor is less than 3/4" to accept engineered, or if you want to align solid hardwood parallel with subfloor planks, then you may want to consider a 3/8" or 1/2" OSB underlayment.
- If you are gluing you really need an APA rated underlayment to accept the glue on both 1st and 2nd. It will make any future work much easier.

Those are the basics at least. The flooring instructions will tell you how they want it too.
 

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Discussion Starter #14
Glue assist means you nail the flooring but put a bead of glue perpendicular every _"o.c. per manuf instructions.

Any flooring you put down you might have to cut door jambs and bottom of door slabs. Exterior doors should be fine with the slider track or threshold raised above the subfloor.

What is the flooring you are putting down? Engineered (12mm-15mm) or solid hardwood (3/4")?

Based on subfloor being not that unlevel as you said in post #4:
- If you are nailing either, you can put them right on top the subfloor. Any high spots can be sanded and low spots shimmed with the felt paper. Note if the existing subfloor is less than 3/4" to accept engineered, or if you want to align solid hardwood parallel with subfloor planks, then you may want to consider a 3/8" or 1/2" OSB underlayment.
- If you are gluing you really need an APA rated underlayment to accept the glue on both 1st and 2nd. It will make any future work much easier.

Those are the basics at least. The flooring instructions will tell you how they want it too.
Thank you very much. Based on this read it seems one should always out something over wood sub floor like I have. I'm using solid hardwood flooring.

http://www.hardwoodflooringtalk.com/forum/particle-board-osb-subfloors-underlayment-types-t385.html
 

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Quarter inch ply will not level zip. But back in the day 3/4” hardwood tongue and groove was routinely installed over the type of subfloor that you have.
 

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Discussion Starter #16
Quarter inch ply will not level zip. But back in the day 3/4” hardwood tongue and groove was routinely installed over the type of subfloor that you have.
And your right, there was hardwood flooring right on the diagonal sub floor in the pic...we ripped it up. There was no hardwood flooring on the other sub floor on the 2nd floor( the wider one). Can we install hardwood directly on it?
 

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And your right, there was hardwood flooring right on the diagonal sub floor in the pic...we ripped it up. There was no hardwood flooring on the other sub floor on the 2nd floor( the wider one). Can we install hardwood directly on it?
They did use hardwood for hundreds of years before plywood. :biggrin2:
 
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