Airbnb announced this week a new product: "Rooms." Now, when you search for a place to stay on the platform, there's a filter to look for a single room that you can rent out. That's right: just a room ...

As many American cities grapple with an affordable housing crisis, one of the cheapest types of rental housing is now under threat — single room occupancy units, also known as SRO's or rooming houses.