1) You can brace or block the joists per standard construction, but what might be easier is to strap the bottom edges of the joists. Typical strapping is done with a 1x3, but a lot of times I'll simply use a 2x4. Run a 2x4 across the bottoms of the joists, perpendicular to the joists. Add a dab of PL adhesive and use a couple of screws at each fastening point. You have specific needs here, so spacing the 2x4s as you need will work very well. What it does is if a single joist wants to deflect downward, the strapping transfers that load to the adjacent joists as well. So it's good as a floor stiffener. For a washer/dryer set up, it also dampens the entire floor platform in terms of the possibility of the spin cycle causing the floor to reverberate. The strapping serves the same purpose as cross-bracing or solid blocking between the joists. It's code-approved, though code only requires it for 2x12 joists, with the strapping being made of 1x3, and the strapping spaced every 8'. The strapping is more effective long-term than bracing or blocking, due to fitment, installation, and shrinkage issues. 2) Do the whole floor. There are only restrictions on maximum spacing (every 8'). So if you make it every 2', or 3', or 4', no worries. Strapping is also easier because you're not wrestling with any of the utilities that take up space between the joists. 3) Your joists span 8-1/2'. For simplicity, why not do run three pieces of strapping? One at 1/4 span, one at half-span, the other at 3/4 span. Just a little over 2' spacing. 4) 3/4" ply over the diagonal boards is plenty. It does not have to be exterior grade. 5) Your floor sandwich can be made up of: -Tile -Ditra -Floor heat wires encased in SLC (no wires under the washer/dryer area through, see comments later) -Plywood underlayment covered with SLC primer -Diagonal plank subfloor -joists I usually advocate a small platform under the washer/dryer stack. It's more for damping than load spreading. I've done sandwiches of plywood/cement_board/plywood, or plywood/MLV/plywood. MLV is mass-loaded vinyl. Screw through the top layer of ply, through the middle material, and into the bottom layer of plywood to secure it together. Or just use construction adhesive. I drill a hole through the middle of the platform sandwich to accommodate the flood pan's drain line. I usually put a square of rug pad on the floor. The inexpensive, maybe 1/8" thick, rubbery mesh or open weave type of rug pad. It acts as a bit of a damper, but also holds the platform in place. I then set the platform on the rug pad. Then put the flood pan over the platform with the drain plumbed through the hole in the platform. Then set the washer in place and the dryer on top of that. I recommend you tile the entire floor, but again, no heating wires under the location of the washer. You'll be putting the sandwich platform on top of the tile in that area, and the insulative value of that platform can shorten the life span of the heating element. Pricklypear, the Ditra-XL is simply thicker than regular Ditra. It really wasn't designed for a specific tile size. It's sole purpose is to allow the thickness of "Ditra plus tile" to match up with the thickness of a typical hardwood floor.

I have a 27"- 28"ish wide closet for our Bosch (it's 23.5"). It was as wide as we could go. My only recommendation is that you confirm where the plug is on the stack unit you get before you do any electrical. Fiance wanted the plug low and now the cord is too short to plug in and getting the unit into place is really hard. You may want to give yourself a bit more room than we did. It will save you a lot of hassle. Many of the units by Bosch and Miele are only 24" to 26" wide, you would have to be more concerned about depth and door swing on a front loader. Even those fairly cheap stack able Thin Twins by Whirlpool/Kenmore/Maytag (whatever) are often 24" to 27" wide but then vary on depth. They are frequently "full size" ore close to it. I just caution you against making the same mistake we did with electrical. We did not make the mistake with plumbing though. Make sure you put your hookups in a accessible place. We already needed to turn our water off when one of the hoses got knocked off when we put the unit it place (the Bosch tech did it even). We were sure glad that those hook ups were on the side instead of the back. Much easier in a tight spot. It was worth the cost to move that small amount of plumbing. Good Luck!

I am interested what you find out because former owner had W/D in upstairs hall (kids) bath and we moved it to basement since there was no room to actually store detergent, fold clothes, etc. Now we are remodeling and are struggling to find a place on first or second floor since we know it's better for resale (though we may not be selling for many years) Would it be on the order of $5,000 to run new plumbing into a closet? Is it worth it when we already have the plumbing set up in an alcove in the bathroom? Is it really better to take up MBR closet space than to put in a kids bathroom? There's absolutely nowhere on first floor we can fit a W/D.

We love our Bosch 24 inch washer but will need to replace the dryer. The Bosch dryer we have is vented. But Bosch doesn't produce vented dryers anymore. Any recommendations? We love the Bosch washer. We don't love vibration.