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The floor on my main level is sagging and I want to add a post in the basement to correct.

The main level floor beam with the sag (shown in red) consists of a 4x12 sistered to a 2x12 and is currently only supported in the basement by the purple walls. This beam supports the main level floor joists (2x12s, 16" spacing on center) in both directions with face-mounted joist hangers which are nailed to the beam but not the joists. As a result, the sag in the red beam has allowed the orange joists to also sag at this end since they are only supported at the opposite end by the exterior wall. But the green joists are held rigid by the blue walls, which is causing a significant and sudden dip in the floor as it moves from the end of the green joists to the sag of the red beam and orange joists.

I am assuming that I should position the post over one of the 4x12 joists in the crawlspace, but will it require a post directly beneath it in the crawlspace? Also, can the post go directly onto the basement's 2x6 floorboards, or will it need some additional base or footing?

diagram of beams and support boards

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  • What is the open span between posts/walls of the main beam? Open span of plus 14 feet should have posts, but support posts need to be on footings, not just placed on the slab. Footings should be designed by a structural engineer. Picture/s are missing.
    – crip659
    Commented Apr 26 at 21:12
  • Load bearing supports(walls/post and beam) need to be supported from the bottom(basement/crawlspace) with footings/foundation walls.
    – crip659
    Commented Apr 26 at 23:23

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