Ins. Code, § 2051

(a) Under an open policy, the measure of indemnity in fire insurance is the expense to the insured of replacing the thing lost or injured in its condition at the time of the injury, the expense being computed as of the time of the commencement of the fire.

(b) Under an open policy that requires payment of actual cash value, the measure of the actual cash value recovery, in whole or partial settlement of the claim, for either a total or partial loss to the structure or its contents, shall be the amount it would cost the insured to repair, rebuild, or replace the thing lost or injured less a fair and reasonable deduction for physical depreciation based upon its condition at the time of the injury or the policy limit, whichever is less. A deduction for physical depreciation shall apply only to components of a structure that are normally subject to repair and replacement during the useful life of that structure.