TomCow

Would 8x2 timber be OK for that span? How much are posi joists?

I'm looking at spanning floor joists over 5m and was seeing if sandwiching a piece of flat bar between 6x2 would stop it sagging.

Reading online about joist spans and 6x2 timber limit. I was thinking about putting flat bar between two bits of timber maybe 4x2 and using them as support to prevent the sag. Would that work?