I love this photo: Mom and dad, two kids and a new puppy, grandma embroidering away in front of the fireplace. If you see it, you know I'm writing about multi-generational families. When it was taken, living with mom and dad was not all that common in the United States, but this is changing quickly. According to Kelsey Campbell-Dollaghan of Fast Company, more and more Americans are living with more generations under one roof. She writes:

… for complex reasons that still puzzle researchers, multigenerational households are now on the rise once more. As many as 41% of Americans buying a home are considering accommodating an elderly parent or an adult child.

Actually, I'm not so sure researchers are puzzled or that the reasons are all that complex.

Multigenerational family living is growing among nearly all U.S. racial groups, Hispanics, most age groups and both men and women. The share of the population living in this type of household – defined as including two or more adult generations, or including grandparents and grandchildren younger than 25 – declined from 21% in 1950 to a low of 12% in 1980. Since then, multigenerational living has rebounded. The number and share of Americans living in these households increased sharply during and immediately after the Great Recession of 2007-2009. Since then, growth has slowed a little but has remained much more rapid than the growth before the recession.

Pew graphic about multigenerational living Graphic: Pew Research Center

According to Pew,

We've covered this issue before on MNN, writing about the "club sandwich generation" — the baby boomers who are coping with elderly parents, kids and grandkids. I predicted then that we were going to need a lot of triplexes.

babies born in USA How many babies were born each year? (Photo: U.S. Census)

It's a few years later, and we have a lot more sandwiches and not a few clubs. The issue basically comes down to two prime movers: demographics and economics. Note the two peaks in the graphic above: the high peak of the baby boomers, and then the build-up of the millennials, who now outnumber their parents.

As Campbell-Dollaghan notes, the baby boomers moved out early and got their own houses, often far away from mom and dad. "The advent of commercial air travel and the rapid expansion of American suburbia made inexpensive, single-family housing — and cross-country travel — attainable for more and more people."

The houses — whether in cities or in the suburbs — were pretty cheap. I bought my first house for about three times my annual salary, which as a young architect wasn't very much. If I had the same job today and was buying the equivalent house with today's salary, it would cost about 20 times what I earned. But now that boomers have these valuable assets, they don't want to leave; fully 90 percent of them say they want to age in place.

Many of these aging baby boomers have been or are dealing with their own aging parents. It's a struggle when they are far away. My wife's mother was only an hour away, but when you get to the point that you're doing that trip twice a day, it becomes very hard. Many of those baby boomers are thinking about what's going to happen to them in a few years; most can't afford retirement homes. Suddenly, the idea of having the kids close by starts to look very attractive.

Then we have the millennial generation. From a demographic point of view, this cohort is huge, bigger than the baby boom. Unlike their boomer parents, they can't find affordable housing where they want to live, near where the jobs are. Many have massive student loans to pay off and jobs that don't provide a great deal of security in this so-called "gig economy." The idea of moving in with the parents may not look very attractive, but it's better than the alternatives.

row houses in Philadelphia Row houses in Philadelphia: some are singles, some are duplexes. (Photo: Lloyd Alter)

Campbell-Dollaghan notes that some builders are selling homes specifically for this multigenerational market, notably Lennar with its NexGen homes. We pretty much dismissed these in an earlier post noting that the houses were in the middle of nowhere, totally car-dependent, took up way too much space and resources, and were not, in fact, flexible at all. But we have to change the way we think about house planning, and return to a much more flexible form. I've seen these in the United Kingdom, Philadelphia and Toronto, writing earlier:

This is how a lot of houses were designed a hundred years ago, when lots were smaller because people didn't drive. Town houses often had a stair along one wall and were easily sub-dividable; Many got broken up after World War II to accommodate returning soldiers and many have been turned back into single family dwellings.

toronto house A 'Toronto special' from the '60s: It's a single, double or triple depending on how you use it. (Photo: Lloyd Alter)

This shouldn't be a matter of choice, but should be a matter of regulation by zoning bylaws and building codes. Design flexibility, greater density and multifamily zoning should be built into the fabric of our housing.

We have 70 million aging baby boomers, most of whom own houses, and we have 75 million millennials, most of whom will never be able to afford houses. There are 33.6 million empty bedrooms in the U.S., (177,734 in New York City alone) yet we have millions of millennials who can't find affordable housing. Some of these bedrooms are in houses that could be converted and adapted; others could simply be shared.

As the baby boomers age and the millennials have their 1.7 kids that they can't afford day care for, it's likely that a whole lot of them are going to be moving in with mom. We should make it easier to do so.

Lloyd Alter ( @lloydalter ) writes about smart (and dumb) tech with a side of design and a dash of boomer angst.

More millennials are moving in with their boomer parents
Building codes and zoning bylaws should make it easier for more people to do it.