When I was doing my main floor laundry I paid special attention to the requirements of my W/D set. My instructions stated to place the set next to a load bearing wall. I have joist 16" on center and they are relatively short at 8 or 9' long. So there is no spring to the floor system. I have a 1..5" subfloor. Then a 3/8" underlayment, followed by an uncoupling membrane by Latacrit, then finished with my tile. The membrane and tile I don't consider adding strength. The strength comes from the joist and subfloor setup. This is how I understand it but I am not a professional builder or tiler, just a DIY'er.

There have been post where individuals report a lot of bounce to their floors with a W/D in use. I believe these floors are the ones that have long joist and the W/D set is set nearer the center of the floor system where there is no support. It becomes a trampoline. This is especially important with a front loader. I don't know about top loaders.

If you use tile, you will want a very stiff floor system anyway, so that flexion of the joist don't crack the tile, with or without the W/D setup. There is a formula to use to calculate joist length, thickness, and spacing, to determine appropriateness for installation of tile. Natural stone takes an even stiffer floor.

Thank you for all of the detailed information! We did the floor joists 12" on center, rather than 16" and they are about 8-9 feet long. The W/D will definitely be next to a load bearing wall, and I think there is even a strong beam underneath them (not 100% sure). Sounds like we should be ok for tile. Would my tile installer know that formula that you mentioned?

He probably knows the formula but it is over at the john bridge forum. At the top of the page there is a link to the tool that allows you to calculate the floor stiffness. It is called "Deflecto". When I beefed up my bathroom to do stone tile my DH put in extra joist from below in the crawl space. They ended up about 9" on center. It is one stiff floor. I bet your laundry room will be fine regardless what type of floor covering you put on it. Check out the Deflecto link and see just how stiff you floor is. I would link the JB forum to this post but GW doesn't like it and wont allow the post to go through.

I chose a porcelain tile and haven't regretted that. It's super durable and 10 years later still looks new. There are many styles and sizes at good price points. And with the way these tiles are made now, you can get anything from a ceramic tile look to porcelain tile that resembles hardwood.