# crowned joist / uneven floor



## shawn99 (Oct 24, 2007)

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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## JazMan (Feb 17, 2007)

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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## sammythebull (Oct 25, 2007)

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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## JazMan (Feb 17, 2007)

Hey Sammy....that is bull.:wink: 

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.

Jaz


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## sammythebull (Oct 25, 2007)

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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## JazMan (Feb 17, 2007)

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.

Jaz


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## dasajame (Feb 4, 2008)

*I have similar problem*

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.

David


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## Bud Cline (Mar 12, 2006)

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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## ididit (Jan 31, 2008)

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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## dasajame (Feb 4, 2008)

*Thanks*

Bud and Ididit,

Thanks for your prompt reply and help! I'm going to give it a try.


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## MikeKy55 (Nov 4, 2009)

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.


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## dasajame (Feb 4, 2008)

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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## MikeKy55 (Nov 4, 2009)

Thank you for that. I'll give the others time to chime in before I proceed.


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## ididit (Jan 31, 2008)

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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## AllanJ (Nov 24, 2007)

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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## Big Bob (Jul 27, 2007)

PLEASE note (readers of this thread) you must sister (repair) the joist you have cut. Proper repair will depend on load, span and joist size. Get this wrong and your new tile WILL crack.:furious:


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## Bud Cline (Mar 12, 2006)

"Nails won't work folks!:no:

Bolt the members together tightly.


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## ididit (Jan 31, 2008)

Big bob. Not to be an a-hole or nothing but I dont believe I read where anybody was NOT going to sister in another joist. 
Bud--- Yes bolts will bring the joist together tighter and fine if the guy wants to buy $20 worth of bolts to get enough in. About $2 worth of ring shank 16d or even sinkers will do the job. Thats why I mentioned c-clamping the two together first to pull them tight. Put in 3 nails in a virticle line every 16" alternating from one side of the joist to the other the full length and it'll be fine. I do this on framing girders on new homes, only using a few 16d sinkers and a BFH (use clamps if you dont know how to hammer) to pull the two together tight and finnishing with nail gun. On the other hand if he put in a full length sister it is not all that important to get the two tight together. I'd just do it for good measure.


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## Bud Cline (Mar 12, 2006)

Whatever!


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## Gary in WA (Mar 11, 2009)

Bud is correct. If you *cut *the joist and sister a new one, nails alone won't work. The new joist needs to be a minimum as long as the old minus, the width of the joist from each end, and *through bolted*, staggered, with* bolts at each end *to transfer the shears. If leveling (raising) the floor above with a new joist (sistering), AND the old joist is intact, you need bolts but* not *at the ends. Page #134: http://books.google.com/books?id=1u...nepage&q=sistering joist with plywood&f=false

Be safe, Gary


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## MikeKy55 (Nov 4, 2009)

When I did mine, I cut the joist in about 3 places across the span, put about 500 pounds of free weights on the spot and gave it a few days. It settled and then I sistered another 2" X 12" X 8' against it using liquid nails and 3" deck screws. The screws are 12" apart and there are 4 rows across the length. I left the weight on it for 2 or 3 days after that to allow the adhesive to set.
Mine was bowed up, so I won't have to worry about it going back down.


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## ididit (Jan 31, 2008)

GBR in WA said:


> Bud is correct. If you *cut *the joist and sister a new one, nails alone won't work. The new joist needs to be a minimum as long as the old minus, the width of the joist from each end, and *through bolted*, staggered, with* bolts at each end *to transfer the shears. If leveling (raising) the floor above with a new joist (sistering), AND the old joist is intact, you need bolts but* not *at the ends. Page #134: http://books.google.com/books?id=1u...nepage&q=sistering joist with plywood&f=false
> 
> Be safe, Gary


I dont recall that the op had a saging floor or for some reason the load has changed and the floor now needed to be stronger than it was. If so then the joist will need to be beafed up. We are talking about a joist with a high crown in the middle of an open space that needed to be leveled out. If you have room to install a full length joist, the only reason it needs to be fastened to the old one is if the flooring is joined on that joist. Otherwise just sitting the new one beside will be just as strong as it was before. Only fasten them togeter to keep the squeek out. What if he completly removed the old joist? Does he suddenly now need a double? Remember it was good enough before. It was not sagging. Nailing together with 3 16d ring shank nails every 16" with a heavy helping of subfloor glue between joist will be as strong if not stronger than a few bolts.


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## Gary in WA (Mar 11, 2009)

I was answering post #7, when it changed to cutting a joist to lower it. Read your reply in post #9, giving an inexperienced DIY the idea of using an 8' 2x12 on a cut one possibly spanning 17'5"---21'11", with possibly 7' to each bearing from the second joist ends. The problem with giving someone an option, is they would take the 8' choice (if only in transport), not knowing how unsafe it is. I was clearing that up in it should be bolted and longer (within the thickness, 12" of bearing) so a reader doesn't get hurt. 

Be safe, Gary


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