A phenomenon called subsidence could be the result of poor soil quality or rising water levels — but not all cases are reported to the city.
Alvin Henry was on his way to work on a Wednesday morning in April when his daughter called from his home to say she heard a bang.
He rushed back to his semi-detached, three-story house in Canarsie, where he discovered that the floor had opened up. Tiles were cracked and furniture in the spare bedroom tilted towards the center of the room. In the garage, a lawn mower, leaf blower and other equipment tipped into a crevasse in the concrete floor.
Since that spring day, Henry, 64, has not been able to move his family back into their home of over two decades, as he’s still working with an engineering firm on repairs.
It was “a catastrophe,” he said, and it wasn’t the first time it had happened in Henry’s neighborhood. He had known of at least five other homes on his block where bottom floors collapsed.
The local block association president, Edmundo Mckenzie, told THE CITY that he’s heard about many more instances in the area — and that one happened in his own home.
While the exact cause of Henry’s damage is still being determined, engineers and scientists said that what’s called “subsidence” (the ground caving in), may be the result of the soil quality on which the home stands, or of water below ground that puts pressure on the structures.
Either cause threatens buildings throughout the city, and there’s a risk that subsidence may increase with the effects of climate change.
“Subsidence hasn’t been considered a big issue in New York City because so many of us are on the great glacial moraine, on the rock,” said Beth Malone, a program director at NHS Brooklyn. “We’re gonna have a lot more of this stuff going on because of the rising water tables that are gonna be seeping in as a result of climate change, as a result of rising sea levels.”
The Floor Sunk Eight Inches
It’s hard to know how many times houses in Canarsie — or elsewhere — have been affected by collapsing ground floors. What neighbors in the area understand is by word of mouth. Unlike Henry, who called the city to report the damage, most homeowners have simply made the repairs quietly, without notifying officials, and stayed in their homes throughout.
Henry did the right thing, according to the Department of Buildings, which sent inspectors over to check.
“For their own safety and the safety of their families, we strongly urge New Yorkers to let the City know about hazardous conditions in their buildings,” DOB spokesperson Andrew Rudansky said. “Collapses like this one could be indicative of larger structural issues in a building that may make it unsafe to occupy, and also pose a danger to the public.”
But Henry said he regrets calling the city, since nearly five months later, his house still bears a vacate order from DOB while he awaits the structural repairs. The family is staying with their daughter, who owns a house nearby.
“It was a little weird at first, but I’m comfortable now,” Henry said. “There’s a lot of stuff that you don’t have that you’ve left at your home and you just have to either make do or buy new stuff.”
At Henry’s house, the floor in what had been the guest bedroom had sunk at least eight inches below the walls, making the walls appear as if they’re floating. The engineering firm Henry hired indicated that the house’s foundation was broken, but the cause of the collapse would only be determined once digging commenced.
Michael Barry, a structural engineer who formerly worked for the DOB, reviewed photos of the damage and said it looked like a sinkhole, or an empty space underground that may have opened up and caused the collapse.
“My guess would be that the soil [condition] is extremely poor,” he said.
Poor quality soil may be unstable and not be able to bear weight. The soil’s movement may open up a space in the ground beneath the structure, causing a sinkhole. A sinkhole can also be caused by water below ground, whether naturally occurring or a leak.
Canarsie sits just off the northwestern curve of Jamaica Bay and is bordered by both Fresh Creek and Paerdegat Basin. Like many other New York City neighborhoods, most of Canarsie was once a tidal salt marsh.
That marshland was filled in during the late 19th century, including the land below Henry and his neighbors’ homes, according to Eric Sanderson, vice president of urban conservation at the New York Botanical Garden, who studies ecological history.
“Salt marshes have a rich, organic, peaty soil that will break down into carbon dioxide over time as they decompose, so it is possible that settling of the landfill is causing the foundations to break,” Sanderson said, “but I imagine there could be other causes as well.”
Separate from a sinkhole, water below the ground — whether from a leak or a high water table — may also weaken a structure.
Klaus Jacob, a Columbia University geophysicist, surmised that a high water table may play a role in structural damage to ground floors. As THE CITY previously reported, groundwater is expected to rise with sea levels, which will rise between seven inches and just over 2.5 feet in under 30 years, according to estimates by the New York City Panel on Climate Change.
“If you have an impermeable lid in the ground, like a basement, it puts pressure on the floor from below (and if the water table is high enough, also on the basement walls), which can push the floor upwards and walls inward,” Jacob wrote in an email.
Other Canarsie Collapses
Henry’s neighbors, who live in the attached home next door and asked not to be named, said they’d experienced a collapse in their ground floor in early 2021 due to water damage. They hired an engineer to make the repairs without notifying the city and stayed in their home throughout.
So did Mckenzie, the block association president, whose ground floor cracked in the middle, from the back of the house to the front before Hurricane Sandy hit in 2012.
As the issue of collapsing floors have taken more precedence in recent neighborhood meetings, Mckenzie said he now understands what’s at stake.
“You have families that are living in homes, and if it cracks, that’s one thing,” he said, “but imagine if your house just happens to collapse in some way — then you’re talking about lives.”
Barry, the engineer, said homeowners who have heard of sinkholes or floor collapses in their neighborhoods could test the quality of the soil beneath their homes and take measures to underpin the exterior walls for more structural support.