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Old 11-29-2014, 07:07 AM   #1
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Adding additional floor joists to lower deflection


Currently I have a cape cod. 2nd floor joists are 16" OC 2x6 spanning 21.5 with a load bearing wall running up the middle effectively making my spans around 11'. Based on my calculations that puts my deflection at L/182. It will be carpeted so that's fine. My concern is I'm going to be putting drywall for a 1st floor ceiling. And I can only imagine it's going to crack with that much deflection. If I add a second 2x6 to every joist (not just sistered but supported on both ends) my deflection goes to L/364 which is much better for drywall. House is gutted currently so adding full 2x6 not just sistering is actually less work.

Thoughts?

Ignore the terribly framed center load being wall. Not sure what they were thinking. I am reframing it correctly.
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Last edited by 03silvers; 11-29-2014 at 07:09 AM.
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Old 11-29-2014, 07:07 AM   #2
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Adding additional floor joists to lower deflection


Picture of ceiling joists
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Old 11-29-2014, 08:10 AM   #3
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Adding additional floor joists to lower deflection


Can you go up to 2x8's or 2x10s?
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Old 11-29-2014, 08:32 AM   #4
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Adding additional floor joists to lower deflection


what is it like walking up there ?
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Old 11-29-2014, 08:34 AM   #5
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Adding additional floor joists to lower deflection


Isn't that new number good enough for ceramic tiles? For sheetrock, I'd put 2x4 furring strips across the joists, 5/8" sheetrock and have the 4' ends float between the bays.
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Old 11-29-2014, 09:51 AM   #6
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Adding additional floor joists to lower deflection


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Can you go up to 2x8's or 2x10s?
I cannot go up in size without redoing the upstairs floor and also loosing valuable headroom upstairs. I'm only at 7'7" currently.
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Old 11-29-2014, 09:53 AM   #7
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Adding additional floor joists to lower deflection


Walking up there feels very solid. It was always finished bedrooms. No noticeable bounce. The existing 2x6 are from 1929 but are not rough cut dimensions.


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Isn't that new number good enough for ceramic tiles? For sheetrock, I'd put 2x4 furring strips across the joists, 5/8" sheetrock and have the 4' ends float between the bays.
I'm not sure I follow what your saying. I do not want to lose headroom downstairs by adding additional 2x4s
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Old 11-29-2014, 11:10 AM   #8
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Adding additional floor joists to lower deflection


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I cannot go up in size without redoing the upstairs floor and also loosing valuable headroom upstairs. I'm only at 7'7" currently.
Add steel "sisters" to the 2x6's and maybe some blocking.
1/8" or even 12ga sheet cut to size and through bolted should be adequate.
Using a layer of 3/4" plywood -with the steel sandwiched- is even better.

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Old 11-29-2014, 11:17 AM   #9
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Adding additional floor joists to lower deflection


I appreciate all the other suggestions. But time and money are obviously a factor. I'm really just wanting to know opinions on adding additional 2x6 joists supported on both ends just as the existing ones are
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Old 11-29-2014, 11:47 AM   #10
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Adding additional floor joists to lower deflection


Blocking would help as it will keep them from twisting and lock them together with the ones beside them.
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Old 11-29-2014, 03:10 PM   #11
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Adding additional floor joists to lower deflection


What?... Unless your joists are bowing when some one is upstairs walking around its silly too go nuts thinking about. Sheetrock would be fine
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Old 11-29-2014, 05:27 PM   #12
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Adding additional floor joists to lower deflection


You also have to figure in weight of furniture and such, not just a person walking on the floor. Sistering in the 2x6s would also ensure you can add tile at a later date.
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Old 11-29-2014, 06:06 PM   #13
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Adding additional floor joists to lower deflection


There is a load barring wall, from the pics right in the center of the room which would need to be for a 2x6 joist run like this
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Old 11-29-2014, 06:30 PM   #14
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Adding additional floor joists to lower deflection


Silver....

My thoughts are that your idea is smart... given your circumstances. L360 is standard max.... you're gutted and now is the time to do it... should cover you in the future for any changes....

(I would probably add some blocking also... ties your floor performance all together)

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Last edited by MTN REMODEL LLC; 11-29-2014 at 06:32 PM.
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Old 11-29-2014, 08:28 PM   #15
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Adding additional floor joists to lower deflection


Im in the process of remodeling a house that is exactly like what you have, I have doubled up the floor joist in the whole house and there is no noticable deflection and it passes code. Only difference is my house was built in 1936 and the 2x6 were ceiling joist with storage above that was converted into living area and it destroyed the plaster

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