A tax method of depreciating property by separating a functional unit—such as an office complex—into allowable components that may be depreciated over a shorter time period than otherwise permitted for the whole. For example, nonresidential real property improvements must be depreciated over 39 years.One may allocate the cost of some components, such as fencing, lighting, security systems, and carpet into categories that can be depreciated over 5 or 7 years,providing larger tax deductions.