Let's look at what people do to get by in terms of housing. I focus on housing here because as the author's of the living wage calculator note, housing (and childcare costs) tend to be higher in metropolitan areas.
In densely populated parts of the DMV (e.g. downtown Silver Spring, Columbia Heights, Ballston), people with low wages often double and triple up in one bedroom apartments. This happens in 2 bedrooms too, but not as often. Why? Well, for starters, there just aren't as many 2- and 3-bedrooms in the DMV as there are 1-bedrooms. And, their scarcity makes them more desirable, and thus more expensive.
In my last apartment in DC there were two families who lived in 1-bedroom apartments in my building. One family included 2 parents and 1 child. The other had 2 parents and 2 children. I don't know what their wages were, but I do know that squeezing into a 1-bedroom apartment was what they had to do to afford to live in our neighborhood in the city. Even the small houses in the area cost upwards of $800,000. I understood why they were willing to make the squeeze. The schools were good and access to buses downtown was literally out our front door. But, it was a sacrifice too. A 1-bedroom with 3 and 4 occupants is definitely cozy, but exceptionally crowded. There's too little closet space, not enough privacy, and only one toilet for the all of you.
Millennials do this teaming up as well. Although many of the millennials flocking to DC are young professionals, it is useful to keep in mind that being young and professional doesn't mean you can afford DC's luxury rents (Numbeo puts the average 1 bedroom rent in the city center at $1,984.38). This is especially the case for interns and entry level staffers on the hill, and almost anyone at any level working for an NGO. There's a reason a lot of millennials haven't left the nest, or have returned to it. They can't afford to rent.
People do this in the suburbs as well. There, though, the house is what gets piled up with people. In households where people don't make a living wage, it is not uncommon for multiple generations of families live together under one roof. Sometimes, families will also rent out their basements, or even single rooms. Housing costs in DC's suburbs are lower than in the city, but they are still high, especially when compared to suburban locations in smaller cities, or in cities that aren't experiencing urban booms (e.g. Cleveland or Detroit).
For people who don't make a living wage, the idea of a nuclear family in a single family house is just that--an idea. It isn't a reality, or likely to be one anytime soon.
