The correct response regarding the 80% rule is:
Insurance companies will require the policy holder take 80% of the replacement cost of the entire property in coverage, or they will reduce the reimbursements by a proportionate amount.
This principle generally means that to receive full compensation for a loss, a property owner must insure their property for at least 80% of its replacement cost. If they do not, any claims made may be subject to a penalty or reduced reimbursement.