Renting out a house AND the above-garage apartment

[Lauren Keen Aumond]

Hi everyone. My boyfriend is looking into buying a house (currently 2/2/2, easily converts to a 3/2/2) that has a 2/1 garage apartment. When doing analysis, should we assume rents separately and add them together? What I mean is this: do we look for 2/1 apartment comps and 3/2/2 house comps and add them together? Being new to REI, my concern is that the same people that would rent a 3/2/2 SFH are not the same that would be comfortable living with another tenant on the property and maybe we should assume the house's rent would be lower. On the flip side, maybe the apartment would rent for more than a typical apartment because of relatively fewer neighbors.

*I searched BP for another string with this topic and couldn't find it. If you know of one, please post the link for me. I'd prefer not to create double work for you if you've answered this question elsewhere.

Thanks!