Floor span decisions

[Ice]

Hi all,

I'm not new to construction by any means, but this issue is worrying me a tiny bit.

I'm raising a kitchen floor to give legal height to a basement. The original floor was put in terribly...hacked together after a fire some years ago before the current owner bought the place. It slopes down about 2-1/2 inches over 16ft span, and is noticeable as you walk on it. So, to correct this, AND give a usable room downstairs, it's been decided to redo the floor. And while we're at it, it's been decided to make this 20x 16 kitchen into 2 rooms, giving another bedroom to the place.

Only issue is, I don't quite have the room height-wise for 2x10, so I'd like to step down to 2x8, even if it means doubling them, on 12" centers.

The whole span will be sitting on framing built internally in the basement (to correct terrible walls and allow a nice covering to finish). Framing will also be on 12" centers, and the uprights will almost certainly be 4x4" posts, with a 4x1-1/2 header across them. all spanning joists will sit on top of the 4x4's.

So, will 2x8's doubled (glued/bolted together) be ok for a 16' span (actually only 15'8")?

To me it seems it would be fine, but I'd just like some input.

Thanks,
Ice.

[Don_P]

I used 40psf dead load+10 psf live load, 50 psf total. At 16' span on 1' ctrs x 50 psf= 800 lbs/joist

Assuming no point loads... uniform loading, etc, a double 2x8@12" ctrs just fails in deflection using #1/2 SPF. #2 dougfir or SYP or better just passes.

[Ice]

Thanks for the reply Don!

Sooooo...8's wont do it huh, unless DF? And even then you say 'just' passes.

Dang.

Well, in that case, looks like it will have to be 2x10's then, and I'll have to rip out the ceiling and raise it a bit (it's suspended...after a fashion). I was hoping to avoid it, but you have to do what you have to do.

Thanks anyway.

Mike.