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Unsupported interior wall


edee_em's Avatar
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03-21-18, 11:47 AM   #1  
Unsupported interior wall

A bit of background:

I unfortunately have 5/8" osb in a room where I want to install hardwood. All those in the know say the minimum is 5/8" plywood or 3/4" osb. I don't want to change the floor height so I will be removing osb and replacing with 5/8 plywood. I have 3/4" hardwood installed on the first floor over this osb (didn't know better at the time) and it is like walking on bubble wrap with all the creaks and pops.

In planning this out I came across a non-load bearing interior wall (master bath on other side) that is running parallel to joists and about 11' long. It is sitting on a joist maybe 1/2 to 3/4". It looks like it is being supported more by the subfloor than the joist.

I need to cut out that subfloor on the bedroom side so I was thinking of putting in some blocking/bracing or sister the existing joist to give more width and support for the wall. The subfloor under the wall right now will be staying in place

My questions are:

First, is a sister joist a good solution and would a 2x4" glued and screwed be okay or should it be wider? Current joists are 2x8". The sister would not sit on any sole plates or be supported in any other way.

Second, if blocking/bracing I was thinking about attaching some 2x lumber between the two joists (think blocking) on either side of the wall every 16" or so running the length of the wall. Again, can this bracing be 2x4" or should it be larger?

Thanks for your time and expertise!

 
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03-21-18, 04:47 PM   #2  
IMO, a glued and screwed 2x4 sistered alongside would be fine. It's just acting like a cleat for 16" of subfloor, so no big deal. If you have to sister 2 pieces, using 2x6 might be better so that they lay flat... you are sure you don't get a couple twisty 2x4s.

 
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03-22-18, 07:11 AM   #3  
Thanks for the reply XSleeper. Your bit about the span, "It's just acting like a cleat for 16" of subfloor, so no big deal." caused another question. The span would be the 11' length of the wall, not 16". Did you reference the 16" cleat as an example and would the sister still work over the 11' run?

 
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03-22-18, 06:22 PM   #4  
If the joist when sistered does not have sufficient exposure into the bedroom to accept the new subfloor then you need to install cross braces either with hangers or toe nailed to give the subfloor proper support to prevent another "bubble wrap" scenario.

The reason the OSB standard is 3/4" is that the cleats blow out the other side and reduce the holding power of the fasteners in the OSB. 3/4" material will not have the fasteners, driven at a 45 degree angle, blow out the back side of the subfloor.

 
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03-23-18, 09:11 AM   #5  
Very good point Czizi. The sister will not be thick enough if I use 2x lumber. I would need to use 3 or 4 2x pieces to get into the bedroom side sufficiently assuming the wall is not on the existing joist enough.

So I'm probably better off going with my option 2 since I will have to provide support for the new subfloor. In your opinion is 2x4 lumber okay for this type of support? Any need to go to 2x6 or 8 as the original joists? How far should they be spaced, 16"?

 
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04-03-18, 08:15 AM   #6  
Cross brace replacement

Came across a cross brace that is in the way in this project. I have been installing bracing between joists and will install cleats between these braces to support that edge. The issue is that the cross brace is in the way for one of the sections. I immediately thought to remove it but if they were important enough to install in the first place it might not be a good idea to remove it. So, looking for suggestions on how to get around the cross brace. I was wondering if a solid brace could be used to replace the cross brace. Thoughts?

 
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04-03-18, 05:24 PM   #7  
Would be nice if you could upload a picture or two. Go to the advanced reply area and look for the insert picture. Browse your pc and click upload. May be necessary to reduce the size of the picture to meet max file size to upload.

Solid block bracing will replace the cross bracing and provide sufficient load carry from the adjacent joists to each other.

 
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04-04-18, 02:55 AM   #8  
Picture

A picture is worth a thousand words! To make sure, should the solid brace be 2x8" like the joists or can it be 2x4"? Intuitively, I don't like the idea of a 2x4 because it would only be "bracing" the top half of the joists or does that matter?

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