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Sistering attic floor joists to main level ceiling

Sistering attic floor joists to main level ceiling

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  #1  
Old 07-05-18, 03:52 AM
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Sistering attic floor joists to main level ceiling

Hello all,
I have recently started the process for reinforcing my second floor. The second floor was finished but had some bounce.
After tearing up the floor I found that the existing 2x6s are cantilevered in place holding up the roof trusses (about 1.5ft overhang passed the structural support below).
In the picture, you can see the incoming electrical connection conduit, that runs along the exterior wall. The structural support starts where the lath & plaster ends (where I have that 2x4 floating).
Since I do not need to reinforce the roof support, can I just install the new 2x8s spanning the load distance?
And, would it be better to sister to the 2x6, or to center between the existing joists?

I plan on using PL wood glue and 12d nails if sistering.
I am aware that this may damage the ceiling below, but it needs to be done.

Thanks
 
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  #2  
Old 07-05-18, 04:33 AM
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What is the span? Sister them to the existing. This will surely create a problem at the top of your stairs... hope you have a landing that won't be elevated. A cup grinder would make quick work of that plaster, albeit dusty. Chipping with a putty knife works too, just slow and tedious.
 
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Old 07-05-18, 04:34 AM
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How far do the joists need to span?
 
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Old 07-05-18, 10:51 AM
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Thanks for the replies,
Span is 10ft, my plan is to run the new 2x8s only the distance to the outer wall, and sister them to the existing. What I was unsure with, is if the new joists are ok not connecting to the roof/ trusses, the same way the 2x6s do. I assume so, since they are only for the extra floor support, but I want to be sure before going ahead.
​​​​​Also yes, the stairs are being redone as part of the next phase
 

Last edited by thesampson; 07-05-18 at 01:46 PM.
  #5  
Old 07-05-18, 02:55 PM
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Doesnt matter if you connect to the rafters but you will want to add blocking on the ends then insulate behind. You don't want cold air channelling down the floor joists.
 
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