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Old 12-16-2009, 06:50 PM   #1
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Can you use 2x4 for sistering ?


I am working in my 30 year old house over a finished basement. I plan on installing 3/4" oak strip flooring when I get my floor issues solved. The house had 11/16" particle board over 1/2" plywood, 2x10 joists on 16" centers. I have removed all the particle board and will replace it with 3/4" plywood. The floor is unlevel around the hearth area. I have planed on removing the subloor back ten feet from the low area. I am not crazy about cutting the subfloor at the edge of the plate, but I will have to do that. I thought that I would shoot a benchmark off of the level joist and then sister up to level with the low joists. I need to gain about 3/4". Since I am looking at this from the stand point of just getting level, would a 2x4
do the job.

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Old 12-16-2009, 07:00 PM   #2
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Can you use 2x4 for sistering ?


2x10 joists 16 inches on center may be adequately strong based on the span. If they are strong enough, consider shimming the joists to support the plywood rather than going to trouble of trying to sister a 2x10 with a 2x4 and forcing the 2x10 up 3/4 of an inch. That sounds like a recipe for trouble. A 3/4 inch shim may be all you need.

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Old 12-16-2009, 08:37 PM   #3
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Can you use 2x4 for sistering ?


Pull some strings level and see what you really need.Then cut shims. The 3/4 inch on it's own is sufficient over 16" centers -- put the shims down right on top of the studs, and screw the new layer through them into the joists. I'd put subfloor glue everywhere.

If you are going to sister them to level out some sag, then you probably need 2x10s. Jack up to make it proud of where it needs to be and attach the new one. Use a few screws and let the jack down to see if it's where you want it. Adjust as necessary.

Last edited by pyper; 12-16-2009 at 08:40 PM.
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Old 12-16-2009, 09:11 PM   #4
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Can you use 2x4 for sistering ?


"I am not crazy about cutting the subfloor at the edge of the plate," ----- Be sure to add blocking under the wall if joists run with the wall before cutting plywood. Any glue under existing plywood? I agree with Daniel's method, especially if the bearing beam needs help and the joists are not the problem. Rented laser levels work well for this with their 360* level line to measure down from. If you do need to sister: http://www.finehomebuilding.com/PDF/Free/021184090.pdf Use nails, not screws which don't have the shear required, and they meet the current IRC building code when permanently attaching them.
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Old 12-16-2009, 10:13 PM   #5
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Can you use 2x4 for sistering ?


I suppose this job would be easier if I had access to the joist from below,
but unfortunately I finished the basement long ago. I do not want to tear the basement ceiling out.
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Old 12-16-2009, 10:21 PM   #6
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Can you use 2x4 for sistering ?


Quote:
Originally Posted by Stude View Post
I suppose this job would be easier if I had access to the joist from below,
but unfortunately I finished the basement long ago. I do not want to tear the basement ceiling out.

Do the floors bounce? If there's no bounce then don't worry about it and just shim them from the top.

Pull strings to keep the floor in a plane between all the different openings/doors into the room. Don't worry about if it's actually level unless you have a reason to. All things being equal level is good, but matching existing floor surfaces is probably more important.

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