There can be shared laundry onsite, shared parking, shared (yet separated) yard space etcAs for the math portion, I run my rental comps on rentometer and compare it to other ADU's or 1/1 units and their rent amount.

They value furnished common areas, high-speed Wi-Fi, security, in-unit laundry, and smart home technology.

I was thinking it may be closer to a "wash" or, maybe only slightly more only bc w/ a duplex at least we aren't paying for two exterior wall materials for two sfh?

to Revolution Laundromat ... hey, it's a cash business (like car washes), this happens!

Monico,  It gust so happened that I washed a great webinar put on by Dave Meyer from BP.  

Make it so that there is enough capacity for them to do their laundry, but not so much that the dryer becomes a weapon between the 2 tenants if they do not get along. 

We do in unit laundry, as well!

Relocated the laundry room, Finished the basement, made the kitchen and living room an open concept, extended the deck and added a back patio door, and more.

Lot of rentals were lacking in unit laundry or a backyard that I need.

In the past people had "laundry rooms" and it was a revenue source, am I looking at this the same way?