There are two vaguely worded achievements in the Skyrim Hearthfire expansion:
Land Baron:
Buy three plots of land
Master Architect:
Build three houses
Does this mean that all three plots of land must be bought in a single playthrough, and all three houses must be built in a single playthrough to earn the achievements? Or could I play through the game three times, each time buying one plot of land and building one house?
Best Answer
Achievements are baked into the saves themselves* -- the file containing your Level 2 Bosmer Thief doesn't know anything about your past life as a level 82 Nord "100-in-Everything". Which is to say, no, you must achieve achievements in a single playthrough.
*Incidentally, this is why it is possible to mod out the "Can't earn Achievements with Mods" feature of Skyrim SE.