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Old 04-30-2019, 01:29 PM   #1
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Subfloor Hump - Sand OSB or Plane Down Crowned Joist?


I will be putting down hardwood floors (3/4" unfinished oak) in my kitchen. At one spot in particular that is about 3'x9' I have two crowned joists that create a hump in the subfloor about 1/4" high at the highest. I will be laying the flooring perpendicular to the worst part of the hump so the subfloor needs to be level.

Would you take a belt sander to the floor and reduce the OSB to 1/2" total thickness (where the worst spot is, slightly less elsewhere)? Will the hardwood floors add enough rigidity and support to make up for the lost 1/4"?

OR

Would you cut out the subfloor and plane down the offending joists?

I am set up and know how to do either but think the belt sander to subfloor option is easiest. But perhaps not the wisest!

Last edited by flipflopper; 04-30-2019 at 01:36 PM.
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Old 04-30-2019, 02:52 PM   #2
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Re: Subfloor Hump - Sand OSB or Plane Down Crowned Joist?


I would NEVER use OSB any where, in any house or structure.


With plywood you could get away with sanding and still have great strength. With OSB, you can try sanding or planing the are, and then support the thin places from underneath, between the joists.
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Old 04-30-2019, 03:06 PM   #3
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Re: Subfloor Hump - Sand OSB or Plane Down Crowned Joist?


Cut out the subfloor nail 2x4s to the joists so the subfloor can be put between the joist so the top of the sub is level
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Old 04-30-2019, 05:47 PM   #4
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Re: Subfloor Hump - Sand OSB or Plane Down Crowned Joist?


1/2" of anything is too thin to hold a nail for hardwood flooring. I would take up the subfloor, and plane the joist. Replace with Advantech subflooring, it is water and moisture resistant.
It is the only I product I would use in a kitchen or bath subfloor.
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Old 05-01-2019, 08:18 AM   #5
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Re: Subfloor Hump - Sand OSB or Plane Down Crowned Joist?


Wow, lots of good responses!

"I would NEVER use OSB any where, in any house or structure."
I tend to agree. I hate the stuff after seeing how a little water penetration can simply erode the floor after a few years. Sanding/planing the floor to 11/16" (it is actually 15/16" I believe) could work but I can't get at the floor without tearing up the basement drywall in the garage. I don't feel like doing this and would rather tear up the floor to do it properly.

"1/2" of anything is too thin to hold a nail for hardwood flooring."
I hadn't thought of this but it's very true. The subfloor is something like 15/16 and not 3/4" as I initially said. But still, it would be too thin. Better to do a job right the first time.
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Last edited by flipflopper; 05-01-2019 at 08:20 AM.
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Old 05-01-2019, 08:23 AM   #6
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Re: Subfloor Hump - Sand OSB or Plane Down Crowned Joist?


Products on the floor that look like OSB are not usually like OSB as they do resist water most times better than plywood. When you build houses in the rain, plywood ply separation is a real problem
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Old 05-01-2019, 08:23 AM   #7
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Re: Subfloor Hump - Sand OSB or Plane Down Crowned Joist?


@Nealtw
This is really good advice and would simplify the work dramatically.

What are the green blocks in your diagram? If I sealed up the edges of the channel I'm left with above the original joists, could I just put down some floor leveler to fill in this gap (and that would be the green in your diagram)?
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Old 05-01-2019, 08:24 AM   #8
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Re: Subfloor Hump - Sand OSB or Plane Down Crowned Joist?


@Nealtw Thanks for the info about OSB. Now that I think about it, the OSB flooring I buy from Lowes (T&G) does seem to have some kind of thin layer like what pressure treated lumber seems to have. Not sure if it's the same but I never thought about it before.

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Old 05-01-2019, 08:27 AM   #9
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Re: Subfloor Hump - Sand OSB or Plane Down Crowned Joist?


Quote:
Originally Posted by flipflopper View Post
@Nealtw
This is really good advice and would simplify the work dramatically.

What is the green blocks in your diagram? If I sealed up the channel I'm left with above the original joists, could I just put down some floor leveler to fill in this gap (and that would be the green in your diagram)?
We have fixed high spots like that but we leave the green areas for the flooring guys to deal with, so I don't know. But you could rip something off the side of 2x4 to put in there.
I think there are a few brands but this stuff only looks like OSB but it does not grow when you water it.

https://www.huberwood.com/advantech/home-advantech
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Old 05-01-2019, 08:29 AM   #10
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Re: Subfloor Hump - Sand OSB or Plane Down Crowned Joist?


"We have fixed high spots like that but we leave the green areas for the flooring guys to deal with, so I don't know. But you could rip something off the side of 2x4 to put in there."

Going from left to right in your diagram, I can see how you get your first course of subfloor level. But how do you get subsequent 2x4s at the right level and in line with the subfloor to the left that you're laying down as you go so as to arrive at a level floor?

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Old 05-01-2019, 08:39 AM   #11
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Re: Subfloor Hump - Sand OSB or Plane Down Crowned Joist?


Quote:
Originally Posted by flipflopper View Post
"We have fixed high spots like that but we leave the green areas for the flooring guys to deal with, so I don't know. But you could rip something off the side of 2x4 to put in there."

Going from left to right in your diagram, I can see how you get your first course of subfloor level. But how do you get subsequent 2x4s at the right level so as to arrive at a level floor?
Pull a tight string a cross the opening, then slip a block under the string at both ends so it is off the floor. Now you can measure down to the good joist and mark the bad ones that same measurement in three places, nail the 2x4 to those lines.

Or just tack down a flat 2x4 across the hole. place a chunk of subfloor on top of the 2x4 and lift it until it touches and nail it there.



Put the 2x4 down in the bay either way so you don't have to fight to get them in.
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Old 05-01-2019, 08:46 AM   #12
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Re: Subfloor Hump - Sand OSB or Plane Down Crowned Joist?


Thanks, great idea!
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