Property is for sale for $100,000.

The homeowner is willing to spend $100,000 to purchase the home and is primarily concerned with the improvement. The condo developer is willing to spend $100,000 to purchase the development rights but will demolish the improvement.

Use is Mutually Exclusive

According to the Whole Equals the Sum of the Parts theory, the value should be $200,000, but, because one use of the property excludes another use, the value is $100,000, i.e. you can't live in the house and build the condo.