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Discussion Starter #1
The 13-1/2' dimension of my living room (1950s construction) is spanned by 2x4 ceiling joists at 18" on center. Before I realized that I had 2x4s under the OSB decking in the attic space, I put a bunch of storage tubs up there. What should I do to make this space available for storage and to provide the rigidity we need for the sheetrock that will replace the ceiling tiles in the living room? Can I sister four 2x4s to each existing joist? Would some sort of angle iron do the trick? So much for having a Professional Engineer inspect this house before buying it.
 

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At a min you would need to install 2x6's on 16" centers
2x8's would be much better depending upon the weight of your storage
My house is from the 50's & has 2x6 as floor joists

If you have anything heavy up there - spread the weight around
If you have an area that has a wall directly below that is you best option for storage right now
 

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Discussion Starter #5 (Edited)
Are you sure it's not trusses?
I'm 100 percent certain that I have no trusses. :) The roof frame forms one big isosceles triangle.

So sistering up half a dozen 2x4s to each existing ceiling joist wouldn't work? Replacing the 2x4 joists with 2x6s seems like it would be a lot of work. I have 2x6 rafters at a 5/12 pitch, so I guess 2x6 joists might fit without my having to notch the top plates. I'll have to put on a respirator and go figure out how much room I have.
 

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Discussion Starter #7
Well, I'm finally getting around to this project. I'm a lot wiser and more experienced than when I first posted this question, but some questions remain.

I'm thinking of adding 2x10 joists centered between the 2x4 joists at 24" on center. How should I fasten these joists to the top plates? Would some sort of simpson tie be the best solution?

A 2x10 joist has a thickness to width ratio of 1:5, so it requires some sort of stabilization. Would the simpson tie be enough to stop lateral movement? If I need to use 2x10 blocking, what would I do about the rafter and 2x4 floor joist in between each 2x10 joist? Should I just avoid blocking at the outer top plates and notch the blocking to fit over the 2x4 joists?
 

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I don't know if your 2x4 rafters will get in the way but you could use 'bridging straps' to stabilize the 2x10 rafters and keep them from rolling on you.
 

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Seems like it would be easier to sister them to the ceiling joists it might cost you 3 more boards on a 20' room. Then you could cap off the open end of the 2x10s with a 2x6 sitting across the top of your ceiling joists. Assuming your rafters are 18" oc you could put a block on your rafter to attach the exterior end of your 2x10 to.
 

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Discussion Starter #10
I'll take a look at the bridging straps. Are you aware of some sort of an inverted joist hanger to attach the new joists to the top plates on the exterior wall? I can't imagine trying to toenail the joists in a such a tight space.
 

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Discussion Starter #11 (Edited)
Seems like it would be easier to sister them to the ceiling joists it might cost you 3 more boards on a 20' room. Then you could cap off the open end of the 2x10s with a 2x6 sitting across the top of your ceiling joists. Assuming your rafters are 18" oc you could put a block on your rafter to attach the exterior end of your 2x10 to.
I was thinking that I would have fewer drywall problems with the 2x10s centered between the 2x4s, but the benefit might not outweigh the additional labor. How would you sister with the big difference in width between the 2x4 and the 2x10? What would you do about the lapped portion of the existing rafters, sister to the "outside?" Wouldn't I want the 2x10s to be in contact with each other?

On a side note, I'll have to double check the rafter spacing, since I may have measured a portion of the house that is not representative of the overall framing.
 

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I would sister the 2x10's to the 2x4's and block the tops with 2x3's. You could also use any 2x material and lay them flat, even with the tops of the 2x10's.
 

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Discussion Starter #14 (Edited)
I would sister the 2x10's to the 2x4's and block the tops with 2x3's. You could also use any 2x material and lay them flat, even with the tops of the 2x10's.
OK, so I'll try just blocking the tops with 2x3s. To clarify, I'll be running the 2x3 perpendicular to the joist in the joist bays and flush with the top of the 2x10s. I imagine the 1.5" dimension of the 2x3 would be facing up, the 2.5" dimension would be facing to the side. At what interval would you block?

Should I bother trying to fasten the new joist to the top plates, or should I just nail the 2x10 to the existing joists and to a 2x block on the rafter to make up the 1.5" gap created by the existing joist?
 

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OK, so I'll try just blocking the tops with 2x3s. To clarify, I'll be running the 2x3 perpendicular to the joist in the joist bays and flush with the top of the 2x10s. I imagine the 1.5" dimension of the 2x3 would be facing up, the 2.5" dimension would be facing to the side. At what interval would you block?

Should I bother trying to fasten the new joist to the top plates, or should I just nail the 2x10 to the existing joists and to a 2x block on the rafter to make up the 1.5" gap created by the existing joist?
Correct, you're perpendicular to the 2x10's. At 13 feet, I'd install three or 4, dividing up the 13 feet. So every 4 or 3 feet. If you stagger them a bit, joist bay to joist bay, you can easily nail them in on the side.
If you can get a few 12 or 16 penny nails into the top plate, it can't hurt. But usually the roof angle at this point, is hard to work around.
You might be able to install 2x4 blocking, it all depends on the actual joist dimensions.
 
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Discussion Starter #18
I noticed that we have several ceiling joists that do not lap over a bearing wall. They must have been supported by a closet wall at one time. Since I was planning on sistering new 2x10 joists to the existing 2x4 joists, the 2x10 joists will not be connected to each other. Should I alter my plan in some way to tie the 2x10s directly together?
 

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If only ceiling joists, “exceeding 2x10”: R802.8 Lateral support. Roof framing members and ceiling joists having a depth-to-thickness ratio exceeding 5 to 1 based on nominal dimensions shall be provided with lateral support at points of bearing to prevent rotation. For roof rafters with ceiling joists attached per Table R602.3(1), the depth-thickness ratio for the total assembly shall be determined using the combined thickness of the rafter plus the attached ceiling joist.” ”

You sound as if there will be storage, different requirements. If this will be a storage floor, you need lateral support at the ends; http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_5_sec002_par025.htm

Gary
 

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Discussion Starter #20
Thanks, Gary. I was planning on putting blocking between the joists, so I guess tying the sisters to each other isn't such a big deal. I managed to crack one of the 2x4s completely as I was nailing. I tried using a hammer at first, but this job definitely requires a palm nailer.
 
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