Archaeologists and architects will tell you that an unoccupied building decays and crumbles much faster than an occupied one.
There's no one to fix a leaky roof or complain about a broken window in a vacant building, which is one of the reasons why so many gems of late 19th- and early 20th-century architecture have disappeared from the depopulated hearts of American cities.
So in a way we Angelenos owe a collective thank you to Regino Mendez, a 60-year-old immigrant from Guatemala, for his contributions to historic preservation in the Pico-Union district, just west of downtown.
Mendez pays $300 a month to live in one room of a gorgeous, three-story, century-old Victorian on South Bonnie Brae Street. His building has gabled roofs and an oval window on the front door, and it's one of several homes on the block designated a National Register Historic District.
"In all of Los Angeles there isn't as tranquil a place to live as this one," Mendez told me, which is an odd thing to hear, given the presence in the surrounding neighborhood of at least a half-dozen gangs with overlapping turf. Inside the old Victorian, however, oak beams and creaking floors swallow noise, and Mendez sleeps soundly after a hard day's work at a local garment factory.
Mendez is helping to preserve that architectural gem for future generations simply by living in it. So are hundreds more families living nearby.
Of Latin American and Korean descent, for the most part, they occupy a variety of properties that are 80 years old or older — among them Egyptian Revival bungalow courts and brick apartment buildings with Gothic touches that were fashionable residences in the silent-movie era.
On the 1000 block of South Bonnie Brae Street, hardly any of the current residents realize they're living in what once were the mansions of well-to-do Angelenos.
Roberto Vargas, an 18-year-old son of Salvadoran immigrants, grew up inside the 1896 Marley-Stone House, a residence that boasts a round turret, in the Chateauesque style.
"It's so old, you think somebody must have died in there," Vargas told me as we stood outside, admiring the building's burgundy and lavender paint scheme. "But it looks nice. And it's even nicer inside. You feel like you're living in a castle."
The Pico-Union neighborhood might be impoverished and troubled by crime. But it is by no means empty — which gives hope to historic preservationists like Karina Muñiz of the Los Angeles Conservancy.
Muñiz has preservationist colleagues in Baltimore, Detroit and other U.S. cities who struggle with high rates of vacancy as they fight to keep old buildings alive. White flight and black flight have left properties empty and defenseless against the ravages inflicted by squatters, weather and time.
Generally speaking, L.A. doesn't have that problem. The main challenge faced by Muñiz and other local preservationists is figuring out how to impart enough history to residents so that they'll appreciate and care for the homes in which they live.
"You take an old home, restore it, you make it beautiful, and you're giving something back to the community," Muñiz said.
I've long admired the old buildings of Pico-Union and the small miracle of their survival despite a century of catastrophes — the 1930s Great Depression, the 1950s frenzy of freeway building, the 1980s crack epidemic.
For me those creaky Victorians are a metaphor for the promise and predicament of modern-day Los Angeles.
Think of L.A. as a big, old house that might be half-empty were it not for Latin American and Asian immigrants. According to demographers, the newcomers and their progeny have likely kept the city population from shrinking over the last decade.
But the new tenants also are a transient bunch. Many are unaware and unconcerned with the city's history. Nor are they entirely prepared to care for something so old and fragile.
Pico-Union native Ricardo Guerrero says the community was overwhelmed by the immigration flows of the 1980s.
"It really started getting bad when El Salvador exploded," Guerrero said, referring to the war in that country and the thousands of refugees it produced. "We weren't ready for it."
Guerrero, 47, grew up in a Pico-Union without iron bars on its windows or steel fences around its yards. Now he works for the Pico Union Housing Corp. Part of his job is trying to rebuild a sense of community and permanence.
In this mission, architectural heritage plays a key role.
Guerrero took me to see an old building on Alvarado Street that was perched on steel beams, floating above the ground like a ship in dry dock. It had been donated by a developer to the Pico Union Housing Corp., which paid to move it a half-mile to this new location.
Once, it was the Tudor-style home of Jesse Jevne, a grocer and banker. But the 1904 building was broken into after the move. Its upper floors were gutted by fire, and its spacious living room was covered with debris and graffiti.
This, I thought, is what all the houses in this neighborhood might look like if no one lived in them.
Guerrero plans to transform the house — which rests on the former site of an immigration detention facility — into a community center. One day, he told me, the area's young people will learn essential preservation skills there.
"It's going to take a year of elbow grease and teamwork to fix it," Guerrero said. "And a lot of coffee and cracking the whip."
There's no big wave of gentrification in sight for much of Pico-Union. Instead, there are the working poor and storefront signs in Spanish and Korean.
But L.A. history lives on in that polyglot place, where the locals perform the essential public service of carrying our past into the future.