A previous version of this article said cracks at least one-eighth of an inch long might be cause for concern. It is cracks at least one-eighth of an inch wide that are worrying. This article has been corrected.

The wreckage of Champlain Towers South, reduced last week to a tangled jumble of steel and concrete, has worried residents of other multistory buildings who want assurances that their homes are safe.

Structural engineers say it is unlikely that other condo and apartment buildings are about to collapse. Buildings in the United States are constructed to have a less than one-in-a-million chance of failure.

“This is an extremely rare event,” Sherif El-Tawil, a professor of civil and environmental engineering at the University of Michigan, said of the tragedy in Surfside, Fla. “And I don’t think this is a typical response that we would expect of any building of this age and design, especially in the U.S.”

But for residents who might now be worried that something is seriously wrong, experts say there are ways to tell and remedial steps to take.

Frequently Asked Questions

  • Who’s responsible for making sure residential buildings are safe?
  • What are signs that my building could be unsafe?
  • Are buildings along the coasts at greater risk?
  • What should I do if I see a warning sign in my building?

Who’s responsible for making sure residential buildings are safe?

Building codes, state and municipal inspection programs, and state laws governing homeowners associations (HOAs) offer several lines of defense against structural failure. The codes, in particular, are stringent and have improved significantly in recent decades, as has the technology used to raise buildings.

Still, there is an active legal industry focused on suing developers for deficient construction, said Evan McKenzie, a professor of condominium and HOA law at the University of Illinois at Chicago. And he said state and city inspection programs only catch deficiencies, rather than preempting problems.

State oversight of HOAs is also somewhat lax, McKenzie said. Laws generally require the associations to produce periodic reserve studies produced by engineers who examine building components and detail their expected failure dates and the projected cost for repairs.

The severity of those laws varies between states. Sandra Gottlieb, an HOA attorney with California-based firm SwedelsonGottlieb, said her state requires associations to complete reserve studies but does not mandate that they actually set aside funds for the identified future repairs.

“It would be foolish to think that all states have that same level of checks and balances,” Gottlieb said. “But I know for years that people have been attempting to move in that direction.”

What are signs that my building could be unsafe?

Buildings are designed to give warning signals before they theoretically collapse, El-Tawil said. A sloped floor could indicate that a column has moved, while a door that will not close might mean the building’s frame is warped. Sloping cracks in the structure — not just the paint — and rust-colored streaks on the outside of the building could also be cause for concern, El-Tawil said.

José Restrepo, a professor of structural engineering at the University of California at San Diego, added that rust on the reinforcing steel inside concrete columns or beams is also worrisome because rust can break concrete as it expands.

Pools of water could also cause buildings to retain the liquid and potentially collapse, Restrepo said. And he said he would be worried about any surface crack that was at least one-eighth of an inch wide.

Are buildings along the coasts at greater risk?

Yes, proximity to seawater poses additional concerns. Salt from that water — or from swimming-pool water — can rust the reinforcing steel inside concrete, Restrepo said. Building codes have been revised to better plan for this issue in recent years, making it more of a concern for older structures.

McKenzie said climate change can exacerbate that issue and cause others. Most construction a few decades ago did not consider the effects of sea-level rise, which during a storm surge can cause water to flow underneath buildings or flood parking garages. In addition to eroding the buildings’ steel, McKenzie said, that water can destabilize the structures entirely.

“If I was in a condo on the beach,” he said, “I’d be very concerned about what kind of maintenance has been done.”

What should I do if I see a warning sign in my building?

People who notice something amiss should report it to their HOA and can alert their municipal government if the HOA does not act, McKenzie said. Renters also have recourse if they are concerned: Beyond reporting the issue to their landlords, McKenzie said people can raise issues in housing court because of city ordinances that govern landlord-tenant relations.

To be proactive, McKenzie said prospective condo buyers should ask for the HOA date of its last reserve study, whether the association acted on the results, the maintenance schedule for the next several years and the funding plan for those repairs. In most states, McKenzie said, a prospective buyer is entitled to a copy of the HOA’s reserve studies once they have gotten a contract to buy a unit.

El-Tawil said prospective buyers should ask specifically about when the building was last checked by an engineer and how frequently those inspections happen.

“I would like to know that the entire building is sound,” he said, “not just my unit.”

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