I had a similar property... pool was incomplete (was 1/2 way done, per the pool company). Here's what I did:
Cost of pool (per pool company as well as invoice): $40,000
Range of adjusted values between properties w/ and w/o pools: $30,000 - $50,000 (buyers in the area typically demand pools per my discussions with RE agents) - sample size: 27 properties with pools, 15 properties without pools.
Sales with 1/2 finished pools: 0 (DUH! :laugh
Determined property has functional, CURABLE, obsolescence.
Reconciled adjustment for properties with pools vs. without pools: $45,000 (hybrid of cost of pool plus middle to upper range of sales comparison adjustments... more adjustments fell in the 45-50K range anyway).
Percent of pool finished: 50%
Adjustment for sales without pools: +$22,500
Adjustment for sales with pools: -$22,500
Cost of appraisal: priceless.
