(a) Each insurer authorized to write and writing property insurance in this state shall be required to become and remain a member of the plan and the underwriting association and to comply with the requirements of the plan and the underwriting association as a condition of its authority to transact property insurance business.

(b) Each insurer shall participate in the writings, expenses, profits, and losses of the association in the following manner:

(1) For habitational risks, the same proportion as its habitational premiums written bear to the aggregate habitational premiums written by all insurers in the program; and

(2) For commercial risks, the same proportion as its commercial premiums written bear to the aggregate commercial premiums written by all insurers in the program.