Duplex appraised using single family comps?

[Kevin Shook]

I just received the appraisal for a duplex under contract.  The appraisal was approx. 8% over the sell price, but I realized they classified it as a single family and used single family comps.  Its zoned multifamily (actually Res with commercial use) with a business office on the first floor and an apartment on the second.   I think it may appraise a little higher when compared to other duplexes in the area.  Is it normal practice to appraise a duplex as a single family?