How long can a house sit before it's not salable?

So much depends where the house is and whether it was closed up carefully. All things being equal, an empty house probably lasts longer in the arid Southwest than in the humid Southeast. All across the country, banks and city governments are finding that, in general, an empty house has a surprisingly short life.

For example, an abandoned house won't last more than a year in wet northwestern Washington state, says Kirk Juneau, an home inspector in Ferndale. "I've seen where blackberry bushes have grown under siding and into the house and vents," he says.

With no one to caulk windows, clean gutters, trim bushes, run the water, flush toilets and turn on the heat, moisture -- death to houses -- seeps in. In just one winter, mold, rot and even foundation cracks appear. Condensation in a cold house turns building materials soggy and weak. Wind rubs tree limbs against siding. The limbs trap moisture and make a gangway for critters that feast on wood, insulation or wiring. When water is shut off without first blowing air through the pipes, freeze-damaged, cracked pipes will leak when the water is turned on again.

New homes, in some ways, can fall apart faster, Juneau says, because they use manufactured wood products vulnerable to swelling and mold. But in other ways they're tougher: Better ventilated and wrapped tightly against the elements, they can stay dry longer.

A house left half built, even for a time, sustains damage that becomes invisible once the place is finished. Moisture barriers aren't meant to be left flapping in the wind. "The longest you'd want to wait (before putting up the siding) would be two months," Juneau says. An exposed foundation can freeze and crack, especially if the site hasn't been graded for drainage and water runs into and under it.

In Miami, a wooden building won't last long if windows and doors are broken by vandals, letting wind, rain, animals and people in, says Cedric Mar, a city official with the title of chief of unsafe structures.

Termites and wood rot take over quickly, he says. Wind blowing through a home can buckle walls and roofs. The city tries to act quickly to pressure owners to repair or demolish abandoned houses. It takes over derelict properties, but because of legal hurdles, that takes a few months or even several years. In contrast, someone who breaks in and builds a fire to keep warm can burn down a house in an evening.