If that area is next to an outside wall or it is easy to get to an outside wall, you could have the contractor install a floor drain.

Put extra stiffeners between the floor joists.

use two layers of plywood on the floor. And tile.

and be careful moving the washer. you need the shipping bolts reattached.

I am in planning stages for redoing my 2nd floor laundry area, so I've been looking into some of the same issues. Regarding floor drains, I don't think it matters whether you have access to an outside wall, as the floor drain can tie into the same drain line as the washer drain. If you want the floor drain to protect the entire room, the floor should be sloped to the drain, which means you need a mortar bed (aka "mud job") over the plywood subfloor, and then a waterproof membrane over the mortar. This adds cost and also would raise the floor by at least an inch. A less expensive alternative is to put the washer in a pan and attach a floor drain to the pan. This would handle most leaks -- for example overflows -- but not anything where water was spraying out from the washer and would thus miss the pan. The Mustee "Durapan" model looks like a good choice for a pan, as it has a removable threshold in front so you can slide the washer forward without having to lift it out of the pan. The Durapan is attached to the subfloor and then tiled around, so the tile and the pan bottom (with the threshold removed) end up at the same level.

Regarding the floor strength: whether the existing joists are sufficient needs to be calculated based on joist size, spacing, and length. If additional strength is needed, the joists can be doubled up ("sistered"). However, the strongest and stiffest floor can still transmit some amount of vibration from the washer to the rest of the house. Anti-vibration pads (I am using "shake-away" pads) help, but some amount of vibration may be unavoidable. Note that a "mud job" under the tile -- for the floor drain -- should also dampen vibrations somewhat, as the inertia of the floor (resistance to movement) increases as the mass of the floor increases.

Thanks for all of the input. I'm still on the hunt for a contractor who I believe is capable of doing a good job. The first two that gave bids seemed a little bit clueless on why it's important to get this job done correctly.

And I'm still trying to convince my husband that it's worth the expense. He's sold on moving the w/d into the basement and creating a chute or even installing a dumbwaiter to get the laundry down to the basement.

We have two small closets on top of each other that would make a good tunnel from the top and middle floors. And having the w/d in the basement would ensure that elimination of vibrations on the top floor.

Anybody have any experience on laundry chutes or dumbwaiters?

Also, what do I do if we don't have the shipping bolts anymore? I'm pretty sure the movers didn't use them when we moved last spring ... have a completely ruined my washer??