Recently, I had a contractor come in to give me a quote on rocking, mudding, and taping an unifinished basement. He noted a span of about 8' of the basement where a pair of 2x4's are holding up the upstairs floor joists, without support from underneath. We'd bought the house like that, and hadn't thought anything of it, but when he indicated it's a potential hazard, I thought, "Yeah, I can't let it go like that." I plan on either replacing that length with 2x10s or shoring it up from underneath with 2x6s and jack studs.
I realize I have to temporarily build two walls to support the joists in the ceilings, but I'm not sure I want to use up so much lumber afterwards (don't really think I have a use for so much spare lumber after the job is done). I want to look into renting the adjustable jacks to use as supports under the temporary wall headers, but I can't remember what those jacks are called? Framing jacks? Adjustable wall jacks?