How would property work in cities that must split apart every generation?

Every city in my setting is built on a giant salt raft crossing a shallow inland sea. Fresh water condenses beneath the raft at night, so routes follow seasonal humidity rather than trade.

A raft must split when its weight becomes dangerous. Buildings are dismantled, families are divided between the new rafts, and neither half can keep everything. I am stuck on property law. Permanent ownership seems impossible when every structure has a mass cost and the community physically divides every generations. Would people inherit rooms, building materials, weight allowances, or something less tangible?