(1) The value of a relevant property shall be determined under this Act by estimating the net annual value of the property and the amount so estimated to be the net annual value of the property shall, accordingly, be its value.

(2) Subsection (1) is without prejudice to section 49.

(3) Subject to section 50, for the purposes of this Act, ''net annual value'' means, in relation to a property, the rent for which, one year with another, the property might, in its actual state, be reasonably expected to let from year to year, on the assumption that the probable average annual cost of repairs, insurance and other expenses (if any) that would be necessary to maintain the property in that state, and all rates and other taxes in respect of the property, are borne by the tenant.