Estimating ARV for Duplex, Triplex, and Quad

[Oscar Beteta]

Quick question BP!  I'm on the search for a small multifamily unit in Montgomery County, PA.

I would like to understand how an appraise goes about estimating the value of a duplex, triplex, or quad. I've read that these property types can be appraised just like any SFR based on comparable sales. However, I've also read that they can be value by the income they produce through the gross rent multiplier (GRM) method. Can someone please shed more light on this for me? If you know any specifics about this subject for Montgomery County, PA - please share as well.

Thanks in advance BP!