It has happened over decades. But like many things in sprawling Southern California, it has drawn attention only when it affects a particular street, neighborhood or city.
In the Mid-Wilshire area, four old homes on Cochran Avenue are demolished to make way for 24 new condominiums.
In Eagle Rock, four-story apartment buildings now line a neighborhood that once had nothing larger than duplexes.
In Northridge, the homes along Zelzah Avenue are gone. Now across from Cal State Northridge, sits a row of two- and three-story apartment complexes.
These are all examples of "infill development," where new construction is taking place on land that once was overlooked or where homes, and even small apartment buildings, are being replaced by townhouse complexes and apartment buildings.
Infill development, the vast majority of which are multifamily projects, is one answer to the region's seemingly insatiable demand for more housing.
"Whether we like it or not . . . infill development provides opportunities to build the city without continuing our urban sprawl," said attorney Dan Garcia, former longtime chairman of the Los Angeles City Planning Commission.
At the same time, infill raises important questions about where new housing should be built, and how much is too much. And those questions loom significant if Southern California is to continue to grow without further--and dangerously--overtaxing the municipal infrastructure--streets, sewers, water supply system and the like.
Nowhere is infill development--and its implications--more evident than in the city of Los Angeles, where densities in some areas already rival those found in Chicago, Philadelphia and even New York.
And there is no sign that the push toward higher density will diminish.
Indeed, under existing zoning, according to city planners, enough infill housing could be added to accommodate 1 million more residents in Los Angeles, which already has a population of more than 3 million.
"I keep thinking the infill will drop off any month now. But it hasn't," said David Lessley, who, as head of Los Angeles' plan implementation division, sees the overall picture of development in the city. "It's obviously here to stay."
The signs are everywhere.
--In the city of Los Angeles, 92% of the new residential construction between 1980 and 1989 was in multiple units, according to Terry Bills of the population research unit of the Los Angeles County Regional Planning Department.
During the first six months of 1988, a staggering 99% of the city's new residential construction was in multiple units, Bills said.
--In Los Angeles County, he said, 74% of the new construction since 1980 also has been in buildings of three or more units.
Those numbers, say regional officials and urban planners, prove that Los Angeles County is not just growing out; it is, they say, growing from within on land that has, in most cases, already been developed for decades with single-family homes.
"Riverside and San Bernardino led the nation last year in the construction of new single-family houses. Los Angeles County was second," said Bills of the county's population research unit.
"But in Los Angeles County, the new single-family housing was concentrated in a few areas like Santa Clarita and Antelope valleys. The infill development was everywhere."
Added Arnie Sherwood, director of community and economic development for the Southern California Assn. of Governments:
"The higher-density development is something that every big region experiences at some point. But I think that most people here are only now paying attention to it because of the congestion."
But as Sherwood and others point out, infill development, particularly in Los Angeles County, began several decades ago and accelerated in the 1980s.
As large parcels of land became more and more scarce, builders in the 1960s returned to undeveloped or underdeveloped areas, constructing multifamily housing projects that would serve and capitalize on the region's explosive growth.
Properties large enough for multiple units were gobbled up by developers, particularly along growing business corridors. So were scattered vacant parcels, even those on hillsides where topography and old construction techniques once made development more expensive than it was worth.
The wave of new apartment buildings, in particular, accelerated in the early 1980s with tax-exempt bond programs that allowed cities and counties to help developers by buying down interest rates, according to Ben Bartolotto of the Construction Industry Research Board.
"The bond program generated a lot of activity in the early 1980s. It and the old tax code, which offered generous deductions for apartment investments, were big factors in adding to the construction of apartments," Bartolotto said.
Although the 1986 federal tax reforms placed severe limits on bond financing for multifamily units, Bartolotto said, the higher-density developments continue.