In Disney Dreamlight Valley, your house can be expanded up to 20 floors total. The sources I found also say the fully expanded house can have 4 rooms per floor , which means up to 80 rooms overall.

What that means

  • The house starts small and gains floors through upgrades.
  • After the early house upgrades, you can keep adding floors until you hit the cap.
  • Community guides consistently report the current maximum as 20 floors.

Cost note

The floor expansion price increases as you go higher, and the later floors get very expensive. One guide notes that the highest floors can reach 1 million Star Coins per floor near the cap.

Quick answer

Max floors: 20.