Replies

1. 
   mgmahan | Sep 18, 2022 03:04pm | #1

   Is there a floor above, or are these just ceiling joists?

2. 
   danielkut | Sep 18, 2022 05:28pm | #2

   There’s a floor above, but no load bearing walls, etc. it’s just a 3/4inch subfloor.

   I got a sort of thumbs up from a buddy who’s a commercial GC who said round tube on 12 inch centers would be overkill but might be simplest and allow for greatest reduction in joist height.

3. 
   ct_yankee | Sep 19, 2022 03:02pm | #3

   You have 2 things to consider: strength & performance.
   - You MAY get the required strength with a shallower member, BUT -
   - You will pay for it in performance. The floor will have a lot of 'bounce' and probably greater deflection. If you don't care about waves in your coffee cup of soap bowl as the bride walks by, then go for it.
   - If a future center island is being considered, don't go here.

1. 
   danielkut | Sep 19, 2022 05:02pm | #4

   We were approved to do 2inch schedule 40 pipe.

   Plan is to sister 2inch schedule 40 pipe next to current joists and then cut joists to match pipe joist.

4. 
   rww0002 | Sep 19, 2022 06:16pm | #5

   Maybe I am misunderstanding your condition, but if these ceiling joists are also serving as floor joists for the floor above, cutting the wood down to 2 1/2" and adding 2" std. pipe @24" o.c. does not sounds like a great idea to me..

   If the joists are spanning the 14' direction with a 30psf live load on the space above you might get something over 3" of deflection in the floor and the floor joists will be overstressed by a factor of 2. Talk about a bouncy floor! This also will not meet any code I am aware of. If this is a ceiling only and there is no living space above it might have a chance of working, but I still bet you notice a ceiling sag.

   If you are adding a center beam of some kind you might be able to make this work, but it is still an odd condition, and you will still need additional depth at the girder. There is a reason that 12" joists were used to begin with (and also a reason you don't see pipe sections used for beams very often - they are not very efficient and do not perform very well in bending).

1. 
   danielkut | Sep 19, 2022 09:27pm | #8

   12” OC.

   Interesting. I thought round tube was much more efficient than square tube.

1. 
   rww0002 | Sep 19, 2022 10:40pm | #9

   Well 12" o.c. is better, but deflection will still likely be over 3x what you would you would expect for standard floor framing and will feel really bouncy The floor may not meet local building code. I would expect to see cracking in ceiling finishes over time and possibly other damage to finishes. I am surprised an engineer would sign off on those steel sizes.

   Square tube sometimes costs a bit more per pound, but square or I-shaped steel sections perform better that round sections in bending. Pipe sections are generally used for columns and or truss members (or better yet - for carrying water..)

   At the end of the day as ct_yankee mentions above, reducing depth of a floor system down to 1/4 of original depth is going to drastically reduce the floor performance. Additionally, adding steel in a wood floor system needs to be thought through and done correctly and the details can be tricky. I think you might spend a fortune and end up with with a minimally better looking ceiling and a floor that feels like a trampoline..

5. 
   bing0328 | Sep 19, 2022 06:58pm | #6

   I still don't understand what you get by raising the ceiling 9 inches.

1. 
   danielkut | Sep 19, 2022 09:19pm | #7

   Give the appearance of 9ft ceilings.

6. 
   mgmahan | Sep 20, 2022 10:43am | #10

   Use 4x12 joists @ 48" oc. Use 1 1/8" plywood for the floor above. Relocate your utilities. Make it an open beam ceiling.