To figure the decrease in Fair Market Value (FMV) because of a casualty, you generally need a compe­tent appraisal.

An appraisal to determine the difference between the FMV immediately before a casualty and immediately afterwards should be made by a competent appraiser.

The appraiser must recognize the effects of any general market decline that may occur along with the casualty. This information is needed lo limit any deduction to the actual loss resulting from damage to the property. ­