(1) With reference to insurances against loss or damage to property, except as provided in RCW 48.12.050, and with reference to all general casualty insurances, and surety insurances, every insurer shall maintain an unearned premium reserve on all policies in force.
(2) The commissioner may require that such reserve shall be equal to the unearned portions of the gross premiums in force after deducting authorized reinsurance, as computed on each respective risk from the policy's date of issue. If the commissioner does not so require, the portions of the gross premiums in force, less authorized reinsurance, to be held as a premium reserve, shall be computed according to the following table:
(4) After adopting any one of the methods for computing such reserve an insurer shall not change methods without the commissioner's approval.
(5) If, for certain policies, the insurer's exposure to loss is uneven over the policy term, the commissioner may grant permission to the insurer to use a different method of calculating the unearned premium reserve on those certain policies.