would sistering a 2x6 onto a old 2x6 be as strong as a 2x10 that should have been used? 24" on centers 14' span

What are u trying to do?

Chuck

I'm updateing, room by room, a older home in northern Wis. This room is 14' x 18'. I'm down to the rafters,studs, and joists. The floor was bouncy. It only has 2"x6" on 24" centers. Trying to get rid of the bounce. Only have room for 2" centers. Trying to get rid of the bounce. Only have room for 2"s now thinking of adding a 2"s now thinking of adding a 2" between the old ones which would give me 12" on center and supporting them all in the center of the span.

Do u have room for girder under floor beams?

What will span be after u put in girder?

Adding 2x6 at 12'' center will help with subfloor and finish floor.

Chuck