[sixeightten]

I have never seen a 2 ply beam in a basement. Not knowing your exact situation, I can only guess, but I think I would go for a 3 ply 2x10 and keep the post spacing as you suggested. If your deflection is only 1/4 or 3/8 as you say, I would be inclined to not do anything, unless I was adding a piano, aquarium, or something else heavy to the existing load.

 

[sixeightten]

“3 ply” meaning (3) 2x10’s with plywood?
As for the sag, the home is gutted and we are working on getting the floors “even” and ready for new flooring. While it’s prob not a huge deal for the flooring install, it’s something that I would rather do now then have to deal with down the road. Flooring will most likely be some sort of engineered wood or bamboo.

Yes, just the 3 ply 2x10. The plywood does not really add any meaningful support, since it is limited to 8' sections. Depending on where you are, the footings will be the most difficult part. Cut the concrete and remove, excavate for the footing, add rebar/concrete.

Another possiblility would be to sister a few 7 1/4 lvl's to the existing 2x8, if you don't have wires/pipes in the way. Adding these every 3rd or 4th joist would add some support without having posts in the way, and also less work.

 

[sixeightten]

I like to compare one job with other jobs carrying similar weights. We build floors with 2x10s and often build staircase openings that are more than 10 ft long and the floor and often the wall above is supported with 2 2x10.

So 2 2x10s nailed together with a post every 10 feet on footing would do the job, no problem. You don't need plywood between them just 5 nails 16" OC.

Neal, I agree with you. I was just overshooting it because of not being there and putting eyes on it. Although, in your case, the joists are fastened INTO the beam rather than sit on top. A 2 ply beam 23' long will be somewhat succeptible to a roll/lean in the center. Now as long as the posts are imbedded, and the beam post connection is good, that wouldn't be an issue.