......I have an order to do a single family 1004 appraisal on a property with a 3,400 house that also has a 2,550 s/f "guest house", per MLS. It an area that is unzoned, and the property is on one tax id parcel. I notified the lender that it is a duplex, as the second house is too large to be considered an assessory unit. But after discussing this with one "chief appraiser", I got another call from another "chief appraiser" telling me that since both houses are on one parcel, it is not a duplex, but it is a guest house. Is there any definitive guideline that is used to determine if it is a duplex or a guest house? There are very few sales of properties similar to this, but there are few sales of any type in this area, and therefore I can't really say if there is market acceptance.