If you don't want your tile to crack from deflection, you need to know more about your construction than just if you are on a crawlspace or second floor. You will need an uncoupling membrane no matter if the subfloors needs to be reinforced or not.

Tile is not set on the subfloor. That Chuck in a truck ''contractor'' is an automatic NO.

Not enough info for the other one. You can do Ditra or cement board as the uncoupler, but knowing the deflection of the floors is still needed for a successful job.

You should be checking contractor's licenses, insurance, and whether or not they have a clue about TCNA standards.

we're putting in a ceramic tile floor in the kitchen- first floor.

Well, um, yes, but unless you are on slab foundation, that floor has joists. You need to know the spacing, height, and span of those joists to see what size tile or what type of tile would be possible.

We had ceramic in our foyer when we built the house...they had to do heavier joists...later we wanted it in the kitchen and it didn't have the heavier joists so it has a tendency to crack in the grout and we have to regrout areas now and then. It has a concrete base so in addition to the tile it can get very heavy. A good installer should be able to look and advise.

The wood is "fine"...it is the SUPPORT FROM UNDERNEATH that is the trick. The DEFLECTION RATING of your subfloor (joist spacing + thickness of subfloor = deflection rating) is the BIGGEST issue here.

Be aware that these subfloors are not built for tile...only if the build is NEW and the design CALLS FOR TILE at the time they are BUILT then the rating will be good enough. Most times (75% or more) the subfloor/joist system has to be reinforced. If they can do it from underneath, that is great. But most times they have to throw down new plywood (floor height raise) + new floor = double the height you thought it was going to be.

Have the flooring installer check the joist spacing and the thickness of the subfloor. A *good* tile setter will know what is required and will tell you how it will work. And yes, if they have to add/supply new plywood then the price for install just went UP...and sometimes by QUITE A BIT. This is the world of tiles over plywood. It is part of why porcelain tiles are some of the most expensive "labor" and "preparation" costs in the business. The tile = $2.99/sf at Home Depot. The install could be as much as $6-$12/sf (depending on where you live and what they have to to do to get this to work). Tile is cheap...but the labor and prep are expensive. It is the nature of the beast.