Highest and best use issue again. There was a very similar thread on the "Urgent, Help Needed" board.
There are three ways to approach any H&B question. The subject property will be worth more:
In its existing use, with or without additional repairs, rehab or other remediation; or,
Converted to an alternate use, like an office or contractor yard; or,
As a site suitable for development under the industrial zoning, less costs of removal of the existing improvements.
Of the three, the first option is the most common, as the existing use is generally considered to represent your H&B use until the underlying land value exceeds the value in its current use. Your client may also be very interested in the remaining economic life of the existing use, as that may be very different from what the physical condition would seem to indicate by itself. If there is a trend toward redevelopment of these uses, that trend should be noted in the report, along with your interpretation of the effects of that trend on your subject property, both in terms of value and the remaining economic life. It's going to be hard for a lender to write a 30-year loan on a residential property with a remaining economic life of less that 30 years. This is another example of how AVMs cannot account for all the relevant factors in loan underwriting, and why the value opinion alone is not always the main issue of an appraisal.
The short cut to this analysis is to see if industrial sites in the area are selling anywhere near the same price level as your subject's listing. If not, then it's still a house as far as the market is concerned. Any external influences can be adjusted for by using comparables with similar or comparable influences. This would be like a house fronting a busy street or located adjacent to an industrial use.
Around here, SFRs on industrial or heavy commercial lots usually get purchased by contractors, towing companies, truckers, or others who have use for the site but still need the structure for their own residential and/or office use. Your market may be very different.
Whatever you do, don't try to gloss over the legal non-conforming use issue. Disclose it and reconcile it with your opinion of value.
George Hatch