DIY Home Improvement Forum banner

Joist span question

3K views 17 replies 5 participants last post by  havalife 
#1 ·
I currently have 2x8 24 oc joist for my kitchen floor, a couple of them where cut completly through by the old owner. Im planing on changing the 2 joist and beefing them up, sistering a second 2x8. Im just wondering how much more strenght does this add? The span is 11'8" with 7" both sides sitting on sinder block and beam.

From what I can find online, 2x8 24oc is good for 11' spans (if the info i found is correct). Would the sistering be enough to bring this up to code?
 
#2 ·
If the original joist was cut completly through as you stated then sistering a joist to the cut joist is not adding any extra support. Why not add a couple more joists and get the joists at 12" on center? That would help the strength of the floor being that you are over spanned already.
 
  • Like
Reactions: Marbledust
#4 ·
I like what simonb said. add new joist and they will be 12'' onc. Also, replace the cut joist like you posted.

If you plan to put tile down your 24" oc will not cut it. In fact 12" oc will only work with ceramic, not natural stone. If you sister them on 12" oc it will work for stone.

I ran your spans thru the calculator on the John Bridges site.
 
#5 ·
I wasnt going to add 12oc, i was going to keep it 24oc and just sister the joists. Can you let direct me to the calculator you used?

I like what simonb said. add new joist and they will be 12'' onc. Also, replace the cut joist like you posted.

If you plan to put tile down your 24" oc will not cut it. In fact 12" oc will only work with ceramic, not natural stone. If you sister them on 12" oc it will work for stone.

I ran your spans thru the calculator on the John Bridges site.
 
#15 ·
I guess if you are good with an overspan then do it the way you want. If you want to do it right then add joists to 12"oc a little more work but then you know it's right.
 
#16 ·
This was my original question that i havent had an answer to yet. Does doubling the 2x8 allow me to go the 12 feet span that is currently there? Would be nice if there was a calculation that can be done to figure out sistering.I know 1 alone doesnt quite meet code these days.

If not then i guess i would have to look at the 12oc option which is not a problem.
 
#17 ·
The calculators that I gave you show a L402 for a 12' span by sistering the joists on 24"OC.

I don't know what your situation is with the lack of a sill and most likely sagging joists but I'd probably go double 12" OC (L/804) to avoid any subfloor deflection between the joists as well, then you can put any surface you want on the finish side.
Wrap the ends of the joists that are sitting on the block wall with a membrane to avoid concrete to wood contact.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top