Hi I am more of a woodworker and finish carpenter than framer and have a question about fixing my home. I have a 1910 craftsman with a huge attic that is framed with full dimensional 2x4s 32 o.c. for roof rafters and 2x4s 16 o.c. spanning 14′ (to load bearing wall at approximately half the span) as floor joists for the attic or ceiling joists for the home. I would like to make the attic more usable and thus need to strengthen the joists (and sooner or later fix the roof). I would like to lose as little headroom as possible and am thinking that there is probably a way to use steel framing or steel c-channel to sister onto the 2×4’s. Ideally, I’d like 6″ tall members if that’s doable. I was thinking they could rest on the top plates or even on a small furring block above to stay clear of the plaster keys and either run the full width of the house (27′) or overlap at the midwall. Again, they’d be sistered on to the 2×4’s. I’ve never seen this type of sistering and asked an architect friend who said she hadn’t either but that it made sense. Is this done and if so where can I find info and span tables for different gauges of steel joists, tracks, or c-channel?