Installing new hardwoods on plank subfloor

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mekman

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Hello - we've recently purchased a home and have begun renovating. We've decided to replace the engineered floors from a previously added-on room with 2-1/4" white oak unfinished hardwoods.

We removed the engineered hardwoods and discovered a layer of MDF. We then removed the MDF and discovered ~6" plank subfloor. The plank subfloor is in good condition with little/no gaps. The house is on a crawlspace, which has a vapor barrier laid down (but does seem like it can get fairly damp).

The plank subfloor runs diagonally across the room. I've read that you need to install hardwoods perpendicular to the planks, and if that's not possible you need to lay a sheet of plywood over those planks. With these planks running diagonally, does anyone think it would be an issue to lay the new hardwoods straight across (without a new plywood layer), creating a ~45 deg angle from the plank subfloor? FWIW, the joists supporting the plank subfloor do run perpendicular to how we plan to run the new hardwoods.

We'd prefer not to add a layer of plywood so that we can keep this room level with the rest of the house. The current plan (assuming this won't be an issue), is to lay Aquabar underlayment over the plank subfloor and nail down the new white oak hardwoods directly over that.

Any thoughts / comments are appreciated. I'm new to all of this, so if anyone has any additional tips/words of wisdom given what we're planning to do, those are also very much appreciated. Thank you!

I've attached a picture for reference which should help give a better idea.

hardwoods1.jpg
 
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DarisMulkin

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Those planks are the subfloor. I have the same in my house built in the 50's. You want to lay the wood perpendicular to the floor JOIST. If you cover the subfloor you want to put down 15lb roofing felt or the like. But I would add a layer of ply down first. My house had hardwood shorts and they squeeked to beat heck. I don't know why as they only had 1 finish nail in each board. I put hardwood back with the plyqwood and no squeeks.

Daris
 

mekman

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We're trying to avoid laying down a layer of plywood so that we can keep this new floor (which will be the new kitchen) even with the rest of the house.

Outside of that, though - it sounds like you're saying it doesn't matter at what angle the new floors sit on top of the plank subfloor, it only matters that the new floors run perpendicular to the joists that support the subfloor. If that's the case, it sounds like we're fine to just lay the hardwoods directly over this plank subfloor (with an underlayment in between).

Any other thoughts/comments? Again like I said I'm new to the flooring game so if it sounds like I may be leaving out any important details or steps, your input is much appreciated!
 

Ernesto

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What Nick and Daris said, you can run it straight, left to right but not at the 45 degree. angle as the subfloor. Perfect explanation if you know wood lingo.
 

mekman

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What Nick and Daris said, you can run it straight, left to right but not at the 45 degree. angle as the subfloor. Perfect explanation if you know wood lingo.

Maybe I was unclear in my initial post. We aren't trying to run our hardwoods parallel with that subfloor, we're trying to run them straight, which would mean they're running across those subfloor planks at a ~45 deg angle (I've added arrows in the picture below to reflect this). I was only questioning if this was feasible because I had read that you need to run your hardwoods perpendicular (90 deg angle) to a plank subfloor...but from what I can gather based on these responses, your hardwoods just can't run parallel to the subfloor planks, but if they're at a 45 deg angle (as pictured), this should be okay.

Am I interpreting this right? Again we do not plan to lay any plywood over this plank subfloor, so I want to make sure we're going about this appropriately. Thank you all for your help!

hardwoods with arrows.jpg
 

DarisMulkin

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Take the plank subfloor out of the picture and think floor Joists. Hardwood is to go perpendicular to the Joist-that is what holds up the subfloor. Reason for perpendicular to the JOISTS is because of the weight issue, It would possibly sag between the Joists if run parallel to the joists.

Daris
 

davidh

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Keep this in mind , installing wood flooring over the subfloor you have now , is subject to do what ever, any kind of movement from any or all of those planks , could in time , pull , push , the new wood floor apart , nails or staples working its way lose, rolling felt paper , over the subfloor , installing flooring creates a moisture barrier for the hard wood floor , ,still not going to help against what the subfloor , does
 

davidh

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That would be correct , if the subfloor r was ply wood , each one of those planks running in that direction , the only way your new wood floor will sag in between the floor joists , is if the floor joists are to far apart , the truth is , , this should not matter because , installing a new nail down wood floor over the subfloor you have now is not a good idea , I know you don't want to hear this , , , plywood , screwed down , then , go from there
 

Ernesto

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Maybe I was unclear in my initial post. We aren't trying to run our hardwoods parallel with that subfloor, we're trying to run them straight, which would mean they're running across those subfloor planks at a ~45 deg angle (I've added arrows in the picture below to reflect this). I was only questioning if this was feasible because I had read that you need to run your hardwoods perpendicular (90 deg angle) to a plank subfloor...but from what I can gather based on these responses, your hardwoods just can't run parallel to the subfloor planks, but if they're at a 45 deg angle (as pictured), this should be okay.

Am I interpreting this right? Again we do not plan to lay any plywood over this plank subfloor, so I want to make sure we're going about this appropriately. Thank you all for your help!

That is why they run the subfloor at a 45 so you can run it either way just not at a 45 with the subfloor. If you want to run at a 45 then you would run it opposite the 45 degree angle.
 

Tyler2981

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Hi, I came across this post because I had the same question, and found this - "As NWFA Guidelines indicate, the only wood flooring you can install directly to a solid board subfloor or an existing wood floor is ¾” solid or engineered wood flooring. These types of floors can be installed perpendicular to or on a diagonal to the direction of the existing flooring.". So I'm going to just screw the hell out of the planks, sand them flat, and install new hardwood over it. How did it work out for you?
 

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