Depreciated costs, yea. $100,000 minus 10% physical depreciation = $90,000 adjustment. Good luck with that. And how much do you give for an over improvement on the cost approach, since there is no data in the first place to figure it's contribution to the value. Some of you seem not to be thinking correctly.
This is getting into unknown, prove it, territory for your work file. These are the appraisals that you wish you never took, for the problems that they can potentially cause. But there are a lot of expert people here telling you, you can do it. rah rah rah.