Farm and Hydroponic tiles being placed on top of existing building

They're supposed to be able to "upgrade" normal tiles, to make it easier to change an existing layout. Insulated tile does the same thing. Are they able to replace other buildings (besides types of tiles)?

That's right, the various 'tiles' can be built on top of each other to upgrade them smoothly without having to destroy the foundation. This should be true for tiles, airflow tiles, mesh tiles, insulated tiles, metal tiles, plastic tiles, farm tile, and hydroponic farm, I believe. If you see it in any other unexpected cases, please let me know!

Oh! I didn't realize it worked between more than just "Tile". It doesn't work if you're trying to replace Farm Tile or Hydroponic Farm; it sounds like that may be a separate bug.

It didn't work for a long time; it was changed in the past couple months to allow "upgrading" in any direction. Same is true of wires and conduits now.

Farm/hydro breaking the rule is also by design at the moment; the harm of accidentally uprooting your farm is greater (and I think more surprising) than just replacing a foundation tile, but I'll give that some more consideration.

I think that makes sense, but what I tried a few weeks ago was upgrading Farm to Hydro, which is a very natural early-game upgrade. I keep wanting to do that when I'm switching from meal lice to bristle blossoms.

It doesn't happen in every fortress, because it depends on how desperate I am for food at the beginning, and whether I had to set up planter pots or could wait until I had farm tiles. But in like half of my bases, there's a period where I have to worry about replacing a bunch of farm tiles, and thinking "okay, if I mark them all for deconstruction at the same time, then the middle ones in the platform will be unreachable, so do I want to try to upgrade them two at a time? Or build some ladders? Or I could mark them all for deconstruction now, and then spend 60 seconds repeatedly painting over the ones that DID get deconstructed with hydro tiles."

Anyway, it's definitely not the end of the world, but if it's easy to make them replaceable with each other but not other types of tiles, that would be cool.