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Old 10-24-2007, 12:06 PM   #1
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crowned joist / uneven floor


I am planning to lay strip hardwood on the main floor of my house (8-9 years old). The existing subfloor is 5/8" OSB. I plan to put 3/8" plywood down as an underlay. The probem is that the floor is uneven in one section. It appears that one joist is more crowned than the others, which has caused a small peak. On one side of this "peak", the floor slopes off approx. 18" - 2' to the wall. The height difference between the wall and the "peak" is approx. 3/8". I realize that there are some band-aid solutions, such as sanding off the peak and using levelling compounds, but I am not convinced that this is the right way to level the floor. It will not be easy to lift the OSB, as it runs underneath the wall. My question is: Should I cut out a section of the OSB and plane the joist, and if so, how should I go about it. I am reasonably handy, but no expert - any help would be greatly appreciated.

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Old 10-24-2007, 04:44 PM   #2
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crowned joist / uneven floor


I'd have to see it to be sure.....but if it's only one joists, and you have easy access from below, you might consider cutting the joists at just the right spot allowing that joist to come down. If the floor doesn't want to go down enough, you jack it down. Once it's where it should be, you will sister another joist to it. Done.

BTW, 3/8" in 18" or so is a lot!

Jaz

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Old 10-24-2007, 11:12 PM   #3
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crowned joist / uneven floor


There is a much easier trick, if your home is a bit older and the joist is not still moving you can skim coat your floor with a self leveling thin set and feather it out from the joist. The smother and the more level your floor is the better. Any undulations or peaks can cause floor failure over time depending. Level the floor put down some multi ply and use a good Taylor adhesive to glue the stuff down or get a floating hardwood Mannington makes a great one. You will never know the difference.
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Old 10-25-2007, 12:15 AM   #4
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crowned joist / uneven floor


Hey Sammy....that is bull.

Shawn has just one joist that is crowned, why are you suggesting that he raise 80-90% of the floor when he might be able to lower just 15%. This way he would also not disturb the height of the doorway leading to adjoining rooms.

Obviously he may not want to do it that way, but might be the best? BTW, you need flat not necessarily level.

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Old 10-25-2007, 08:01 PM   #5
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crowned joist / uneven floor


Jazz I’m concerned that an average guy is going to have a heck of a problem jacking up his floor to remove and cut the joist down or replacing it. If a job like that is fouled up next thing you know your cracking the drywall fowling up your window alignment. That is the type of job you want a good union carpenter or an Amish guy to do for you. Depending on the length of the span this could be a serious issue.

As far as the height goes ur right the multiply is over kill and will build the floor up way to high with out some old school rigging with your trim pieces. I would go with the original plan sand down the peak about a 1/8 and uses a self leveler to fill in the rest. The reason I like a level floor for a hardwood is because over the life of the floor a level floor is a silent floor.

Just as food for thought

We have a possible crown joist think about it how likely are you to find a 20 inch OC joist span in a home 7 years old. That I joist junk is a relatively new method so why is the span of the dip 2 feet wide? Something else is going on here. Plus if this guy dose has 20 oc joists there is no way he can put traditional strip Harwood on it with out building up the sub floor. There will be way too much deflection.

On one side of this "peak", the floor slopes off approx. 18" - 2' to the wall”.

We need a picture of this floor with a 6 foot level across it to see what the heck is going on here.
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Old 10-26-2007, 12:30 AM   #6
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crowned joist / uneven floor


As I said; I'd have to see it to be sure.. Shawn said everything was in plane except for one joist. If that is what is going on, then your worries about drywall cracking and windows don't apply. He is NOT jacking the floor up, he only needs to weaken one joist and then jack it down. He is not going to replace it.

You're right, it would be nice to see a photo with a straight edge on the floor. If the second joist from the wall is crowned, it will not help to pour SLC between it and the wall. You'd be creating another plane altogether. You can raise the low spots with SLC, but high spots have to be lowered.

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Old 08-01-2008, 10:18 AM   #7
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crowned joist / uneven floor


Jazman,
I have similar problem and your suggestion to cut/weaken and sister joist seems like a good solution for my issue. I am retiling bathroom floor and have a very noticable crown on one joist (the other joists all appear level). It appears the previous tiler tried to deal with the crown by putting a grout line directly on joist and tilting the tile slightly but it is still quite noticeable. I have full access under the joist (a 2x12) with a full basement. My questions: (1) How far should I cut the 2x12? 50%? 75%? (2) How would I jack the joist down? I can understand jacking it up but am not sure how to bring it down.

I assume the cut should be at the highest point of the crown.

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Old 08-01-2008, 06:06 PM   #8
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crowned joist / uneven floor


Agreeing with JazMan. This is easy to do, I have done it several times over the years.

You would locate the center point of the offending joist. Then cut the joist "all the way" to the bottom of the subfloor. This can be done easily with a reciprocating saw. You then can use sand bags, cement bags, concrete blocks, anything that has plenty of weight. Stack that ballast on top of the floor and wait. You will see the cut in the joist take on the look of an inverted "V" as the floor corrects itself.

The slower you allow the floor to correct the better in my opinion. Trying to move everything at one time could disrupt other areas.

Can't remember this taking more than a few days at the longest. One time we lowered a reversed crown with the customers piano.

Once the offending joist is where you need it then scab on a sister joist as long as you can get to fit the available space. I always used thru-bolts to join the two together. That way the friction of the two clamped joists won't let anything move and there is no worry about nails or screws twisting or bending under the pressure.
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Old 08-01-2008, 07:08 PM   #9
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crowned joist / uneven floor


I also agree with cutting the joist. Ive done it before too. You can weight it down like bud said then sister a new joist on the side.
Ive even straightend finished walls in a similar way. Circular saw 3/4 the way trough stud on the concave side. Have someone push from the other side while you drive a thin wedge in the cut. Patch cut with drywall mud.
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Old 08-02-2008, 07:47 AM   #10
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crowned joist / uneven floor


Bud and Ididit,

Thanks for your prompt reply and help! I'm going to give it a try.
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Old 11-04-2009, 05:42 PM   #11
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crowned joist / uneven floor


Curious how that worked out?

I have a very similar situation here. The house is about 7 years old and I'm the third owner. In my kitchen I noticed a feeling of stepping down just slightly when I walked thru the room. Funny I looked at this house three times before buying it and never caught it.
I laid a 6 foot level across the floor and found two joist are crowned up 1/2 inch just about in the middle of the room. I did find one of the prior owners had cut one joist, put a shim in the split and sistered another 2 X 10 in place. However, it is next to two others needing the same approach.
What would be the recommended length for the sister joist?
The basement is unfinished, so I have very good access.

Thanks in advance.

Last edited by MikeKy55; 11-04-2009 at 06:11 PM.
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Old 11-04-2009, 08:05 PM   #12
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crowned joist / uneven floor


It worked great for me. I did it almost exactly as Bud described. The only thing I did differently was that I only cut the 2 x 12 joist about 80% through instead of all the way to the subfloor. I then stacked multiple boxes of tile directly on top of the joist in the vicinity of the cut. Over a period of about 1 week, the joist slowly flexed downward to a level position. I then bolted an 8 foot 2 x 12 (4 feet on each side of cut) to the existing joist. It has been a little over a year since I did this and floor remains level. One of the other guys more knowledgeable than me can probably give you a recommendation on the appropriate length of the sister joist. It seems like I read somewhere at the time I was doing this that the sister joist should overlap the cut by a minimum of 3 feet on each side of cut (I'm not positive on the 3 feet number). Hope this helps. Good luck!
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Old 11-04-2009, 09:57 PM   #13
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crowned joist / uneven floor


Thank you for that. I'll give the others time to chime in before I proceed.
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Old 01-12-2010, 11:45 AM   #14
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crowned joist / uneven floor


The longer the sister the better of course. The shortest lumber you can buy is 8' anyway so put the whole thing in (pick out a straight one when at the lumber yard). In fact if you have the room why not put a full length joist in. If you can put a whole one in then cut your old one first, set the new one beside it, weight down the floor till it is tight to the new joist then nail them together all the way down. Some construction adhisive between is a good idea too. You may want to clamp the two joist together with C-clamps also so you dont have to hammer so much to get the nails to pull up tight.
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Old 01-12-2010, 02:03 PM   #15
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crowned joist / uneven floor


Put a few extra nails near the ends of the sister and also near the cut or split in the original joist.

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