2x8s or I-joists (TJIs) for my floor framing

My floor joists don&#;t need to hold insulation (unless I add some later for sound insulation) because my crawlspace has insulation outside the stemwall.  

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I could use 2x8s at 16 o.c. and spend $612 on lumber.  Or I-joists 9.5 inches deep, 24 o.c., and spend $894.

-Are I joists kinder to the planet? In terms of trees used it seems like yes, but what about processing footprint?

-Are I joists a lot easier to use?  I know they&#;d be lighter and more uniform than 2x8s.  2x8s can vary a bit in depth, but it seems relatively easy to modify the depth at the joist hanger if necessary so that all match.  More annoying to deal with: twist, bow, cupping, etc.  Might it come down to the quality of lumber I can get?  I can get kiln dried 2x8s.  I know to put all joists crown up.

-cost of hangers seems comparable.  I&#;m hanging the joists from the sill plate using top flanged hangers, which apparently has the advantage of eliminating a rim joist, which is apparently expensive for I-joists.  

-2x8s give me a little more headroom in the crawl space.  but I&#;d still have about 30 inches even with the I-joists.

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-the joists will be ~18 feet long, with a beam to support in the middle.  Plans don&#;t seem to make clear but I assume the beam is under the joists, not at the same height (so not requiring joists to be cut).

-since crawlspace is conditioned, I think plumbing and electrical won&#;t have to be punching through the joists.  (I believe I joists are easier to poke holes in than 2x material.)

Are there other things I should consider?  I look forward to getting some more perspectives.

Thanks everyone!
Paula

Alex, the answer to your question is blocking helps distribute the load on a single joist to the adjacent joists. The farther away from the concentrated load the less the other joists can help. The bounce you feel when walking on the floor is associated with the floor geometry. If you saw the subfloor between each I-Joist you basically have a T shaped cross section. How well the subfloor is attached to the I-Joist is a critical component, however the depth of the I-Joist contributes the most when it comes to floor deflection or bounce when walking on the floor. You can install an I-Joist that meets all the criteria for bending and deflection, but feels bouncy when you walk. I-Joist manufactures have figured this out and now recommend deeper I-Joists in their joists tables in their published literature. To correct this bounce after the fact requires making the I-Joists stiffer. This can be accomplished by making the web thicker and/or making the bottom flange larger. Adding blocking will likely not solve your bounce issue. Shortening the I-Joist span by adding another support wall in the basement is another solution if it fits within your floor plan. Gluing and nailing a 2x4 or 2x6 to the bottom flange can be a solution that would stiffen the I-Joist, but that may require some engineering to get it right without too much guessing or trial-and-error.

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