FRR
The question is in how you and the client decide to define the appraisal problem, this will help you establish the relevant property characteristics.
If the client wants two separate appraisals because they are going to be treated separtately as loan packages, treat them separately. If they need the appraisal to reflect the value of the two units as if they are one, you can appraise them as one unit. Such a portfolio use by the client is appropriate but it brings with it different market characteristics which would be relevant. In this case, the key difference is that in the first scenario, the buyer could be seperate individuals for each property, in the second scenario, the likely buyer would be a single individual for the combined property. there may be others but this would be the most common characteristic which might change.
Can this change the way you need to view the property in your market ande would it make a difference in value? Beats me, I do not know your market or the properties, that is why your client has asked you as a professional for advice.
Rather than present an example in this post, I would suggest that you get a copy of USPAP 2002 and carefully read the discussion in Advisory Opinion 23 under the heading How the Characteristics of the Subject Affects the Scope-of-Work Decision, example 4 (lines 97-126) on page 213.
All USPAP says directly on this matter is that you must define the relevant charactersitics needed to determine the necessary scope of work essential to complete an appraisal and communicate the results in a manner which would provide meaningful results to your client.
Post back after reading AO-23 if you want to discuss it further. Or call 336-272-7091.
Regards
Tom Hildebrandt GAA