Some people think that curtailing suburban sprawl through “smart growth” — transit-oriented development, walkability, higher densities, green building — is a theory-based movement dreamed up by a bunch of academically minded planners and architects. In fact real-world market forces, not theoretical, are making sprawl-producing planning, zoning and mortgage finance templates increasingly obsolete.

Until recently, these dominant templates embodied widely accepted planning conventions responsive to prevalent market conditions. For decades, subdivision development was America’s primary model for physical growth. New suburban communities encompassed thousands of low-density residential subdivisions comprising detached, single-family homes and the public infrastructure supporting them. Reaching ever farther into the countryside, they encircled older cities plagued by increasingly dysfunctional public education systems, rising crime and poverty rates and shrinking employment opportunities. Perceived as safe, attractive and affordable, suburbia was also where jobs were going.

Suburban planning and zoning templates were predicated on four key assumptions: that America had an unlimited supply of land; that automobiles and road building, thanks to inexpensive and presumably inexhaustible supplies of petroleum, would forever satisfy metropolitan transportation needs; that grouping homogenous land uses, not intermixing them, would best protect property values, especially for residences; and that the only way to realize the American dream was to own and inhabit a mortgaged house.

Today these assumptions have lost validity. Much of America’s land cannot or should not be developed. Dependency on oil and limitless use of cars pose daunting environmental, economic and geopolitical problems. Homogenizing and grouping land uses impede walkability, diminish transportation efficiency, waste energy and promote social segregation, all without necessarily enhancing real estate values. And when homeownership dreams recently became financial nightmares, many Americans discovered that having a house and a mortgage might not be all they were cracked up to be.

Yet market conditions are changing for another reason: demography. Regional and sub-regional populations are changing. Cities formerly shrinking in population, such as the District, are now growing. According to just-released 2010 census data, America’s demographic picture has markedly shifted in numbers geography and ethnic composition.

Whites have become a minority in many urban and suburban areas where Hispanic and Asian populations have steadily risen, and in some areas black population has decreased. The traditional nuclear family — mom, dad, two to three kids and one or two pets — is now a minority of America’s households. Today a majority of households are people, young or old, living alone; couples or sets of unrelated individuals of various ethnicities, ages and tastes; growing numbers of elderly requiring less dwelling space but more living assistance, and single, low-income parents struggling to support dependent children or perhaps a dependent adult.

A more demographically complex society induces cultural and economic shifts, including perceptions about urban life. Reportedly a majority of Americans, especially young adults and senior citizens, now prefer living in walkable neighborhoods and sustainably designed communities characterized by diverse land uses and a broad array of civic amenities. Their close-to-home wish list includes: transit access; plenty of shopping; cultural, recreational and entertainment venues; parks and playgrounds; good public schools; health-care services, and job opportunities. Affordable housing is also on the list.

Shifting demographics, along with increasing consumer interest in a more-urban existence, are redefining the real estate market. This requires rethinking how we plan, regulate, design and build — or rebuild — parts of suburbs and the cities they encircle. To respond to evolving market forces, new templates for truly smart growth are needed. Such templates must do the following:

l  Focus on and fit designated areas within municipalities and suburban counties where new development or redevelopment is feasible and desirable. Growth that is smart and sustainable also means conserving what is valuable, including existing structures and neighborhoods.

l  Proactively supersede conventional, obstructive zoning restrictions, enabling private- and public-sector initiatives that create the kinds of neighborhoods and communities many people desire and can afford.

l  Serve a broad cross-section of people, not just the affluent. In particular, templates must include financial strategies for expanding and maintaining a community’s inventory of affordable housing, especially rental housing.

l  Set high standards for urban design and architecture that address multiple aspirations — aesthetic, functional, economic, technological, environmental — and establish a process for enforcing standards and meeting aspirations.

l  Ensure that rules governing the process of planning, regulation and development are clearly spelled out; that the process is transparent, and that all stakeholders, including residents, public officials, property owners, business interests and developers, participate constructively in the process.

Roger K. Lewis is a practicing architect and a professor emeritus of architecture at the University of Maryland.