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Old 11-12-2011, 02:31 PM   #1
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How to flatten subfloor hump?


I am creating a third bedroom in my house by rearranging existing space. I had to raise a portion of of the floor to match a different floor height and I'm now getting ready to install my hardwood flooring.

The problem is the that old tongue and groove subfloor has a slight slope to it and it creates a hump where it meets my new subfloor. The subfloors meet at the same elevation but the old subfloor needs to be raised a 1/4" at the back wall for the entire subfloor to be flat.

What is the best way to go about this? I can buy thin plywood to build up the old subfloor but it has to be a gradual slope so that it matches the height of the new subfloor where they meet. I don't want to raise the height of the new subfloor because it perfectly matches the height of the subfloor in the hallway (not shown in the picture) and I don't want to have a small lip in the flooring when entering the room.


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Old 11-12-2011, 05:49 PM   #2
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How to flatten subfloor hump?


Is the new floor going in the direction of the board you have laying there?

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Old 11-12-2011, 09:30 PM   #3
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How to flatten subfloor hump?


Yes, the piece of flooring that you see in the picture is the direction I wanted to install the floor. I didn't want the plank subfloor and the hardwood floor going in the same direction, so I don't have much choice.

The only downside is that my floor joists would be going in the the same direction as my hardwood floor.
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Old 11-13-2011, 04:41 AM   #4
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How to flatten subfloor hump?


How far off plane is the strip wood section by the time you reach the wall?

I'd be tempted to add shims under each nail or ripper strips every 12 inches--(think thin furring strips)
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Old 11-13-2011, 04:22 PM   #5
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How to flatten subfloor hump?


The last strip is too low by about 1/4". I can try to use really thin plywood and build up the floor incrementally as I get closer to the wall. I can even use a few extra layers of felt paper to help smooth the step transitions.
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Old 11-14-2011, 06:12 PM   #6
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How to flatten subfloor hump?


While doing more searches online, I found that using roofing shingles is an acceptable method to level low spots in the subfloor. I have some leftover starter strips for my roof that will be perfect for this.

I will lay them in a "stair step" fashion with the first row having 1 shingle, the second row 2 shingles, and then the third row will have 3 shingles. I'll use 15 pound felt paper used to smooth the transitions. This method will get my floor on plane throughout the room.

I'll let you know how it works.
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Old 11-14-2011, 08:05 PM   #7
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How to flatten subfloor hump?


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Originally Posted by loftezy View Post
The last strip is too low by about 1/4". I can try to use really thin plywood and build up the floor incrementally as I get closer to the wall. I can even use a few extra layers of felt paper to help smooth the step transitions.
I've never heard of anyone doing this before putting in a hardwood floor, and I don't think it's acceptable.

If you want to do it right...pull up the rest of the old subfloor...sister in nailers and finish with the plywood subfloor. Now, you have a good base for your hardwood floor. You'll be glad you did.

Were you down to the joists when you put down the new plywood? If so, then why didn't you pull up the rest of the tongue and groove and finish the plywood subfloor?

Are your floor joists in good condition?

Just my opinion.
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Old 11-14-2011, 10:01 PM   #8
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How to flatten subfloor hump?


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I've never heard of anyone doing this before putting in a hardwood floor, and I don't think it's acceptable.

If you want to do it right...pull up the rest of the old subfloor...sister in nailers and finish with the plywood subfloor. Now, you have a good base for your hardwood floor. You'll be glad you did.

Were you down to the joists when you put down the new plywood? If so, then why didn't you pull up the rest of the tongue and groove and finish the plywood subfloor?

Are your floor joists in good condition?

Just my opinion.
My floor joists are in excellent condition. It is a little difficult to explain what I did, so hopefully you can follow without getting confused.

The new subfloor defines my old office space. The office floor was lower than the rest of the floors in the house, so I had to build that floor up with joists to match the rest of the house. Then, I removed a wall to widen the office enough to make it a room. The old wall was located where you can now see the change from the old subfloor to the new subfloor. So no, I didn't mess with the joists in the old subfloor area, but I didn remove tile, underlayment, linoleum, another underlayment, and about 1,000 staples and nails.

I think I'll talk to a flooring guy to see what he says. I definitely don't want to do something wrong and then waste $600 in flooring material and even more time in my labor.
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Old 11-14-2011, 11:26 PM   #9
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How to flatten subfloor hump?


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I think I'll talk to a flooring guy to see what he says. I definitely don't want to do something wrong...
That would be the thing to do - talk to a flooring guy somewhere. There certainly aren't any of them around here to help you. i
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Old 11-15-2011, 12:53 PM   #10
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How to flatten subfloor hump?


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That would be the thing to do - talk to a flooring guy somewhere. There certainly aren't any of them around here to help you. i
Wait, was that a tongue-in-cheek answer? Are you a floor guy, and if so, any suggestions?

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