(1) Introduction.

(a) The sale of improvements constructed on real property is subject to the real estate excise tax if the contract of sale does not require that the improvements be removed at the time of sale.

(b) The transfer of a lessee's interest in a leasehold for valuable consideration is taxable to the extent the transfer includes any improvement constructed on leased land. If the selling price of an improvement is not separately stated, or cannot otherwise be reasonably determined, the assessed value of the improvement as entered on the assessment rolls of the county assessor will be used.

(2) Lease with option to purchase. The real estate excise tax applies to a lease with option to purchase at the time the purchase option is exercised and the property is transferred. The measure of the tax is the true and fair value of the property conveyed at the time the option is exercised.

(3) Improvements removed from land. The real estate excise tax does not apply to the sale of improvements if the terms of the sales contract require that the improvements be removed from the land. In this case the improvements are considered personal property and their use by the purchaser is subject to the use tax under chapter 82.12 RCW.

(4) Documentation. Completion of the affidavit is required for all of the above transfers except a transfer described in subsection (3) of this section, in which case the purchaser must file a use tax return with the department.