Please post what you learn there back over here as this will be of interest to many. We have two areas in our house where there is tile over tile in place for 4+ years, and neither area has evidenced any problems. However, it was a lot of work to do correctly. (It would have been more to remove the tile, which we did try first, because it was STUCK!) In both cases, the lower tile floor was in absolutely perfect structural shape -- no cracks or hollow-sounding spots. And before going over the top, we roughened up the surface of the lower layer to assure good adhesion. Sewhappy - It sounds to me like your seller did a 'quick and dirty' remodel for sale, and probably skimped on the floor preparation since it wouldn't show. Wouldn't show prior to the sale, anyway... It might be worth a little research to see if you have any recourse.

LVP (Luxury vinyl PLANK) is often SUPER THIN (like 1/8"). When vinyl is soft and flexible and THIN it often sinks INTO the groves and hollows sitting BELOW it. We call this telegraphing. It happens to ANYTHING that is THIN and FLEXIBLE. And I mean anything (carpet, lino, vinyl, paint, etc). This is the BIGGEST PROBLEM with laying LVP over tile. You are almost GUARANTEED to see the "tile" floor underneath. The SECOND biggest problem with LVP (or LVT...they are interchangeable terms for some of us) is it normally DOES NOT allow soft underlayment (the squishy stuff used under RIGID laminate or hardwood). And there is your SECOND issue. You must put the vinyl DIRECTLY over the old tile. As I see it, there are TWO OPTIONS for you: 1. Do this properly = jack out the tile, grind the subfloor, throw down Self Leveling Compound (SLC) to give your floor a lovely SMOOTH surface for the vinyl to sit "nicely". The above can cost $2/sf to remove the tile and another $2/sf to grind/level what is left. 2. You SINK the tiles in CEMENT and then lay the vinyl over top. To sink/float the tiles in cement, you need to GRIND the tiles (gives the tile surface a rough finish = something for the concrete to grab onto) and then you have to PRIME the tile (gives the concrete something to hold on to) and then you have to FLOAT the floor (coating of concrete) so that it is smooth. Then you wait for that to dry and then a final sanding/grinding to get rid of any small bumps/bubbles that are ALWAYS present. This should cost $2/sf for materials and $2-$3/sf for LABOUR (that's A LOT of grinding). Sigh....as you can see you are "damned if you do and damned if you don't". I ALWAYS vote to jack out the tiles for one SIMPLE reason: reduction of floor heights. If you ADD more concrete to your tiles, you will cause plenty of upset with your door/trim/appliance heights. That tiny 1/8" vinyl just added 1/2" (or more) of floor height. And that could be a deal breaker for all the doors, appliances and trim in the space. Not to mention the floor height changes where the vinyl meets anything else. There is NO SUCH THING as "cheap" subfloor preparation. You either pay the Piper on the way in, or you pay the Piper on the way out. And if you do it after he leaves, you could find the price is DOUBLE what it should have been - simply because the job had to be done twice: once the wrong way and then once the "right way".

I can attest to what SJ McCarthy explains: the previous homeowner in the house I bought couldn’t be bothered with taking out old flooring before slapping another down. The flooring was so thick that the counters in the kitchen were ridiculously short, and yes: the dishwasher was bricked in! When I remodeled it took my flooring guys six days to jack out four layers of flooring before laying new tile. When all was said and done I found the interior doors and their jambs had been shortened as well! What a huge, expensive PIA to fix. If you’re not going to do the floors right, please just leave them alone. The future homeowner will thank you.

Do you have the clearance for doors etc. if you add LVP above the existing floor? That would be my first thought. It's hard to imagine a floating floor that makes no impact on the hardwood below it, but I guess it would just be around the edges. Are you talking about the whole house?