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Floor structure

diy_Nate | Posted in General Questions on

Hello All.
I am remodling a room  14′ w x 20′ L. The floor joists are 2x10s & 16″ OC. These are whole joists that span the entire 14 width. One side of the joists are resting on cinder block foundation, the other side is resting on pier & post with a support beam.
The current center support beam is 2 2×12’s nailed together with cinder block & board shims that are supporting the beam. Nothing is tied in, the floor has bounce to it that you can see across when beam when you are in the crawlspace watching someone of size walk across it.
My plan to fix this is to dig & pour 4 footings with 12″ diam sonotubes  12″ thick, settting Simpson post supports while concrete is wet.  4x4s screwed into post supports & tie those to center beam then tie the beam into the floor joists.   This is inside a non vented 2-3′ crawlspace.
Regarding the center beam & footings.
Are the 4,  12″ thick footings, and 2  2x10s with 1/2″  plywood sandwiched between glue & screwed adequate support?
Sorry so lengthy.

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  1. Expert Member


    If you spilt the span of the existing floor joists in half with a new beam, that beam will only have a tributary area it is supporting of seven feet. I would only pour three piers. Pour the piers so they are eight feet on centre, letting the beam cantilever over each end, which will increase the strength.

  2. diy_Nate | | #2

    Thanks Malcom. Makes sense. that would be less digging. I could divide the Sonotube into 16" depth instead of 12" depth. What are your thoughts the size of the beam. 2x10's glued & screwed together.

  3. Expert Member


    By halving the span of your joints they become eight times stiffer. That's going to make a huge difference.

    The beam is fine. it makes sense to keep it narrow enough to bear on a 4" x 4". With plywood in the sandwich I wouldn't glue and screw it, just nail from one side top and both at 12" oc.

    The depth of the sono tube doesn't affect the bearing. It's the size of the area in contact with the ground below. If things are well compacted I wouldn't dig at all, but instead form a 16" x 16" x 8" footing with a post saddle right on the existing floor.

    1. diy_Nate | | #4

      Thanks Malcom. 👍

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