The 13-1/2' dimension of my living room (1950s construction) is spanned by 2x4 ceiling joists at 18" on center. Before I realized that I had 2x4s under the OSB decking in the attic space, I put a bunch of storage tubs up there. What should I do to make this space available for storage and to provide the rigidity we need for the sheetrock that will replace the ceiling tiles in the living room? Can I sister four 2x4s to each existing joist? Would some sort of angle iron do the trick? So much for having a Professional Engineer inspect this house before buying it.