From left, Justin Griffis, Garrett Lance, James Arnold and Andrew Krentz share a unit at the Oslo apartment building in Northwest Washington. What makes the Oslo unique is that, in each apartment, all bedrooms are essentially the same size, and each has its own bathroom. (Matt McClain/The Washington Post)

The future shape of housing in U.S. cities and suburbs, including metropolitan Washington, is destined to change significantly. Whether detached, attached, part of a residential cluster or in a multiunit building, more and more dwellings in coming decades will look less and less like the home you now inhabit or the home where your parents grew up.

Future housing types will be influenced primarily by substantial changes in household demographics and lifestyles. Additionally, evolving technological innovations, coupled with economic conditions making homes increasingly less affordable, will affect the future form of housing.

Such changes also will have an impact on land-use planning and regulation, in turn affecting patterns of urban growth, new development and redevelopment in cities and suburbs.

Indeed, long-standing, out-of-date zoning ordinances continue to determine the nature and scope of physical growth and housing, often impeding real-estate-development innovation and market-responsive changes. In many jurisdictions, zoning laws and regulations reflect demographic and cultural norms going back generations.

Most notably, around central cities, zoning overwhelmingly favors low-density, single-family detached home development serving traditional nuclear families. A relatively small proportion of land may be zoned for higher residential densities, whether for detached or attached homes, multiunit buildings, or homes shared and inhabited by more than one family.

Many zoning ordinances still outlaw creation of accessory dwellings within single-family zones. An accessory dwelling can be a separately accessible unit in a basement, an addition to the back of a house, a small apartment atop a detached garage or a modest, free-standing unit built in a single-family home’s back yard.

Often when municipal or county governments try to change residential zoning regulations to allow accessory dwellings, neighborhood homeowners voice opposition. They usually contend that allowing accessory units will change neighborhood character, increase neighborhood population density and make on-street parking more difficult.

Yet permitting accessory dwellings — or homes with shared occupancy — is a very cost-effective strategy for increasing availability and accessibility of affordable housing for both young and aging adults. In fact, neighborhood density is unlikely to increase because many homes, originally occupied by families with five or six members, are occupied by empty-nester couples or a senior citizen without a spouse.

To explain this nationwide phenomenon, the National Building Museum recently opened a visually stimulating, informative exhibition: “Making Room: Housing for a Changing America.” It begins by telling the statistical story of demographic and lifestyle changes in the United States. With colorful, easily understood diagrams and charts, the exhibition asserts that today “our vision of the American household is inaccurate and outdated.”

A snapshot of diverse household percentages supports the assertion: single-parent families, 7 percent; nuclear families, 20 percent; adults sharing with other adults, 20 percent; couples, 25 percent; and single people living alone, 28 percent. Over past decades, the percentage of traditional, nuclear family households has steadily declined while single-person households have steadily climbed.

Other revealing statistics are on display: Forty-eight percent of U.S. adults are single, 32 percent of young adults live at home, 27 percent of children live with a single parent, and 22 percent of Americans will be over 65 in 2050.

The vast majority of existing, conventional detached and semidetached homes, as well as most townhouses, have been built almost exclusively for traditional nuclear families: father, mother, two or three children, and a pet or two. The need for these homes will always exist. But for many other households, the size, interior layout and functional details of such homes are a poor fit.

Today’s real estate market is more diverse and changing rapidly as more people look for homes satisfying their particular needs, lifestyles and budgets. Differing market segments include singles living together, whether young or old; aging couples not ready to downsize; single-parent families; multi-generational households; and households with someone who is disabled. This pertains not only to detached and attached housing in suburbs but also to dwellings in multiunit buildings.

For example, in the past, a typical two-bedroom condominium or rental apartment would have a master bedroom-bathroom “suite” and a much smaller, second bedroom for a child or guest. Today, demand is rising for units without bedroom hierarchy.

The National Building Museum beautifully demonstrates how this can be achieved. At the center of the exhibition, it has constructed a complete, 1,000-square-foot dwelling unit that could be either a house or an apartment. Very much hands-on and experiential for museum visitors, the unit embodies cutting-edge interior design and technology.

Movable partitions and recessed-in-the-wall, pull-down furniture enable transformation of the unit without need for reconstruction. It can be configured to work for a shared, two-person household, for an extended family or for two independent empty nesters.

The kitchen is equipped and detailed with state-of-the-art materials, lighting, appliances, hardware and cabinetry. Countertop height can be adjusted manually or mechanically to comfortably serve people of all ages, sizes and physical abilities, in accord with universal design principles.

Arrayed in the final exhibition segment are photos, drawings and explanatory texts showing numerous built projects, some in Washington, suggesting where future residential architecture and urbanism are headed. Included are shared and group homes; housing for the elderly; repurposed and retrofitted buildings; and new, demographically responsive housing in suburban and urban settings.

Among the featured examples is the four-story “Oslo,” built by Ditto Residential on a small lot on Sixth Street NW in the District. The modern, architecturally sophisticated structure contains nine three- and four-bedroom flats. But what makes the Oslo unique is that, in each apartment, all bedrooms are essentially the same size, and each has its own bathroom.

Clearly, the Oslo apartment units have been designed to be occupied by and shared among several individuals who may or may not be related.

For a thought-provoking glimpse into the future of U.S. housing, visit the National Building Museum exhibition. At the very least, you’ll love the kitchen.

Roger K. Lewis is a practicing architect, a professor emeritus of architecture at the University of Maryland and a regular guest commentator on "The Kojo Nnamdi Show" on WAMU (88.5 FM).