The Surfside condo that collapsed was vulnerable to sinking earth, engineers say. Your house might be too.

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Just days after the collapse of the condo tower in Surfside, an obscure study emerged that the building had been sinking into the earth for years.

It remains unclear whether the settling, or subsidence, of Champlain Towers South was a factor when the 12-story building crumbled to the ground in the middle of the night on June 24, killing 98 residents. But the phenomenon of subsidence occurs throughout South Florida and has been implicated in damage to structures, especially houses, from Key West to Palm Beach.

In its most spectacular form, subsidence (pronounced subs-EYE-dense) appears as gaping sinkholes in Central Florida, where the ground collapses over limestone that’s been dissolving for years, creating cavities that can swallow houses.

In South Florida, where sinkholes are rare and smaller than those to the north, subsidence is more gradual. But when it takes place unevenly, with one side of a building settling faster than the other, it can crack floors, distort window frames and generate lawsuits over insurance coverage.

The South Florida Sun Sentinel identified at least 30 instances over the past 15 years in which houses were damaged by shifting soil. In one extreme example from the 1980s, a Miami skyscraper sank 5 inches immediately after it was built. But in the majority of cases, it’s only fractions of inches over decades.

But those examples are certainly an undercount. Scientists are just now trying to map and measure subsidence in South Florida, not necessarily in response to the Surfside condo collapse but as an attempt to measure the impacts of sea level rise. The state Legislature has restricted payouts to homeowners for subsidence, reducing the number of claims likely to appear in the court record. Insurers don’t have to report cases that they settle out of court, anyway.

But even with the Legislature’s decade-old restrictions, Florida leads the nation in annual sinkhole insurance claims, with about 5,000 per year, according to Mark Friedlander of the Insurance Information Institute. The average claim, Friedlander says, is for about $140,000.

Subsidence has damaged the home of Surfside’s former mayor. In Parkland, about a dozen homes required foundation repairs from subsidence in the past three years. In Palm Beach Gardens, sinking earth cost Constance Bonvechio her house, cracking the ceiling and foundation, and leading to a lawsuit against her insurance company.

“If the decision [of the court] was a sinkhole, I was covered for it,” Bonvechio said, “But I was not covered for organic matter.”

The damage to Bonvechio’s home wasn’t from a sinkhole. Bonvechio says inspectors drilled for sinkholes at least five times. The last time, “they went with an auger underneath the garage where the main problem seemed to be.”

They found pine trees, she said. “There were pine trees decomposing under the house,” causing subsidence.

Bonvechio and her insurance company ultimately settled the case for an undisclosed amount in January 2013, court records show. Unable to afford the cost of repairs. Bonvechio sold the house for its land value.

The new owners razed the damaged structure, refilled the lot, and built a new home.

During the breakneck expansion of South Florida’s endless suburbs, some builders didn’t always drain and fill the swamp responsibly — opening the door to a future of buildings slowly and unevenly sinking across the region.

Though it has not been extensively studied by researchers, anecdotal evidence seems to point to subsidence occurring across Southeast Florida in small pockets, especially in areas where the soil contains organic matter or was not properly prepared.

Subsidence was a major issue during the initial development of the region, when swamp and marsh were first drained. As a 1960s soil survey of Broward County notes, “with drainage, the organic soils are subject to oxidation and subsidence.” The study mentions the Dania, Lauderhill, and Plantation soil formations as vulnerable. It says in order for the soil to be useful for anything other than farming, the topsoil of fertile muck has to be removed and replaced by fill.

“What happens is the guys didn’t do the preparation of the soil by the compaction methods that can be used or they did it half-baked,” said Richard Slider, president of Slider Engineering Groups of West Palm Beach, who investigates the causes of building damage.

That leaves homes with concrete slab foundations placed directly on the soil vulnerable to incorrectly prepared land.

“As a result [of the subsidence], it causes this differential settlement,” Slider says, “and that’s what causes the problem. If the house is settling three-quarters of an inch on one side and a half-inch on the other, that’s a problem because the house wants to bend or break, and that’s what causes the cracks.”

“You have subsidence everywhere,” said Daniel Lavrich, the structural engineer who chairs the Broward Board of Rules and Appeals, which enforces the building code. “Soil tends to settle over a period of time. Whatever soil you have, if you put a heavy load on the soil, it’s going to settle more than if it didn’t have a heavy load on it.”

The house of Daniel Deitch, former mayor of Surfside, is settling. The subsidence has led to an uneven door.

The house of Daniel Deitch, former mayor of Surfside, is settling. The subsidence has led to an uneven door. (Daniel Deitch/Daniel Deitch)

Daniel Deitch, former mayor of Surfside and a current resident, says he has uneven subsidence going on at his house.

“I know the house is on spread footers,” he says of his 1948 home. Spread footers are a type of foundation that distributes the weight of a structure on soft soils. Even with the special foundation, Deitch says he has cracks in his ceiling in one room and a door that has shifted.

Subsidence, if caught early, can be corrected.

City of Parkland building official Bill Tracy has experience dealing with sinking earth. In response to an inquiry from the Sun Sentinel, Tracy said Parkland has had “perhaps a dozen SFRs [single-family residences] that have had foundation repairs due to differential settling,” in just the past three years.

According to Tracy, subsidence issues with seven homes in the Cascata housing development were identified during construction and remediated. Tracey said most of the houses with foundation issues have been 25-40 years old.

“This is normally due to the ground under the slab drying and shrinking over decades.” he said, adding that the houses typically settle in only a ½- to 1-inch range. Engineers sometimes repair the slab using pressure-injected foam that levels the foundation, according to documents provided by Tracy.

But getting an insurance company to pay to fix the foundation is another matter entirely.

‘Cautious homeowners’ need multiple insurance plans

Florida’s homeowner insurance regulations often can leave people with a sinking feeling when they realize that uneven subsidence — and even full-on sinkholes — might not be covered.

Now, if you want to protect your home from subsidence you have to purchase extra insurance.

That’s because Florida law once required homeowners insurance to provide sinkhole coverage, but not coverage for subsidence. Today, it covers only “catastrophic ground cover collapse.”

By about 2010, sinkhole claims across Florida were rising. So in 2011, Florida’s Legislature altered the law to restrict payouts for sinkhole claims to only the most catastrophic cases. That meant that many people whose homes were merely damaged by subsidence in Southeast Florida were often not eligible for payouts.

Stephen Marino, managing partner of Ver Ploeg & Marino, a Miami law firm that represents insurance policy holders, said insurance companies have spent years carving out exceptions to homeowners coverage to reduce their costs. Now, if a homeowner wants coverage for a specific risk like a flood or a sinkhole, they have to buy it separately, he says.

In 1981, a sinkhole in Winter Park opened up gulping down 250,000 cubic yards of soil, five Porsches at a foreign car repair shop, the deep end of an Olympic-size swimming pool, chunks of two streets and a three-bedroom home. Picture taken May 11, 1981. (Red Huber, Orlando Sentinel file)

In 1981, a sinkhole in Winter Park opened up gulping down 250,000 cubic yards of soil, five Porsches at a foreign car repair shop, the deep end of an Olympic-size swimming pool, chunks of two streets and a three-bedroom home. Picture taken May 11, 1981. (Red Huber, Orlando Sentinel file) (Orlando Sentinel)

“In Florida, to be a fully covered homeowner in certain parts of the state, you now have to have a property insurance policy for liability coverage, a windstorm policy, a flood policy and a sinkhole endorsement or separate sinkhole coverage,” he said. “Florida is treated differently than other states because a cautious homeowner has to buy four separate insurance policies for the same structure.”

Not a lot of people do, says Paul Handerhan, president of the Federal Association for Insurance Reform, a consumer-focused watchdog group.

“The broader coverage is more expensive, and I don’t believe many people purchase it,” he said.

One reason might be the high deductibles.

Friedlander, from the Insurance Information Institute, points out that optional sinkhole coverage has deductibles set by law at either “1%, 2%, 5% or 10% of the property dwelling limit. So, if your home’s dwelling limit is $300,000, and you have a 5% deductible, the deductible would be $15,000 before a claim payout is made by your insurer.”

In 2010, sinkhole damage claims in Southeast Florida almost doubled, data from the Florida Department of Insurance Regulation shows. Between 2006 and 2009, Miami-Dade and Broward accounted for only 2.9% of all sinkhole claims state-wide. In 2010, the two counties accounted for 4.2% of all claims statewide.

Hernando, Pasco, Hillsborough, and Pinellas counties, known as “the sinkhole belt,” accounted for well over 85% of all sinkhole claims in and payouts in the early 2000s.

The 2011 laws also had predictable effects. In one 2017 lawsuit out of West Kendall in Miami-Dade, a judge found in favor of an insurance company simply because the house in question had not collapsed — even though the insurance company recognized that the “cause of distress to the property is related to non-engineered fill causing settlement of the soils which caused damage to the home,” court records read.

But not all sinkhole claims go unpaid.

“I myself have 30, 40 claims in the Hollywood area, in the Plantation area, South Miami area, where the engineers for the insurance companies have confirmed sinkhole activity,” says Howard Levine, an attorney who has represented Broward homeowners in sinkhole cases against insurance companies.

Rarer in larger buildings, but possibly more dangerous.

Subsidence has affected at least one other large building in the area. In downtown Miami, the opening of the 47-story building now called Miami Tower was delayed in 1988 after the building sank 5 inches on one side, disrupting the operation of its elevators. Engineers had to remove and reinstall the elevators after the building finished settling into its foundation.

In Surfside, the Champlain Towers building sank at a rate of about 2 millimeters a year in the 1990s, according to a study by Florida International University professor Shimon Wdowinski.

“Two millimeters per year is usually not a big threat,” Wdowinski said, unless the building was subsiding unevenly, though the data from his study cannot speak to that.

Wdowinski used satellite data to determine that the building itself was sinking. He also detected small pockets of land subsidence that were distributed along the western area of Miami Beach, a part of the city that was historically built on fill dredged from the bottom of Biscayne Bay.

But it appears that the Surfside building may have lacked design elements intended to prevent it from settling unevenly, say two independent civil engineering experts who reviewed the building’s plans.

Like most large structures in Florida, Champlain Towers South was built on piles — long concrete rods sunk or pounded deep into the earth that hold the building up in soft or mushy soil.

Atorod Azizinamini, dean of the Department of Civil and Environmental Engineering at Florida International University, says that the plans for the Surfside building lacked any indication that its support pilings were connected by grade beams, which can tie them together and prevent them from settling at different rates.

Mohamed W. Fahmy, a lecturer in engineering at the University of Miami who also runs a structural consulting firm, concurs with Azizinamini’s analysis about the building’s vulnerability to lateral movement caused by differential subsidence.

He points out that the building’s foundation — an almost foot-thick slab of concrete laid around all the piles — does not have rebar connecting it to the piles at both its top and bottom.

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Both Fahmy and Azizinamini said that the design elements lacking from the building don’t prove that uneven settlement actually took place, just that the building lacked an element designed to prevent it.

“You’re going to find out many factors played a role in this thing,” Azizinamini said. “Not just one.”

Allyn Kilsheimer, the engineer hired by the Town of Surfside to investigate the collapse, is skeptical of theories that the building was vulnerable to differential subsidence.

“We’ve done close to a thousand buildings that we have on piles. We don’t have grade beams in any of those,” he said.

Mario Ariza is an investigative reporter for the Sun Sentinel. You can follow him on Twitter @inaminorkey or email him

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