Saying floor joists are normally I joists is a gross overstatement. A floor joist can be almost any size material, as long as span and spaceing requirements are met that meet or exceed load bearing requirements. There are lots of houses still being built that use 2x8, 2x10, and 2x12 lumber to complete a floor joist system. Further, Engineered trusses, similar to roof trusses, are also being used, as well as the Laminated beams ( also used for roof trusses), and the previous mentioned Ibeam or Ijoist. Each joist design has its specific place in the building industry. My favorite design is the engineered trusses. This design is usually used where HVAC, plumbing, and electrical componets can be hid inside a finished overhead area, (such as a finished basement) since those componets can easily be ran thru the truss spaces. Ibeam trusses necessitates placeing Hvac,. plumbing, wireing, etc, under the Ibeam to lessen the chance of dimishing the loadbearing strength of the Ibeam that would occur by boreing or cutting holes thru the Ibeam for the pass thru neccessaties.
The 2x4stud is 93inches long, designed to incorporate the addition of a bottom sill plate as well as a top plate to result in a final ceiling height of 8 ft.
A 2x4x8 is 96 inches long and used where a actual 8ft piece of lumber is needed. If you go to Lowes or Homedepot, or any other lumber supply and ask for a 2x4 stud, you will get a 2x4x93 inch piece of lumber, unless you ask the lip and tounge pierced asst. thats just there for a paycheck that might be helping you, then you could endup with almost anything. Tape measures dont lie. Take one with you when purchaseing lumber.
