"the Dutch are anticipating the flooding of the polders (the reclaimed land with dykes- not Polshaws) by building houses on hollow concrete rafts. The idea is that in the event of flooding, the house will float."

For that to happen it would necessitate a rather complex design of hollow concrete float, and quite an array of equipment. The buoyant uplift would have to be massive to counter the suction holding such a raft to the ground.