A quarter of metro Houston’s real estate — worth some $55 billion — has been affected by Hurricane Harvey, a new report suggests.

As the sixth-largest US metro area, far-flung Houston has 1.6 billion square feet of leasable space excluding single-family homes. According to CoStar, which issued the report on Thursday, 400 million square feet of commercial space in 12,000 buildings has been hit by flooding.

Many of the buildings — $16 billion worth, according to the report — are apartments.

The properties with the most damage will be 175 million square feet inside the 100-year flood zone, it said, which encompasses 20 million square feet of office space and 72,000 apartments.

Another 225 million square feet is in the wider, 500-year floodplain, but was also engulfed by between 20 million and 25 million gallons of floodwater.

“Unfortunately, the number of displaced residents could be far larger than current media reports indicate,” CoStar Group founder and CEO Andrew Florance said.

“Our property-by-property review of the assets in the floodplain reveals an outsized share consists of low- to moderate-income households, including those in southwest Houston, where the bayous overflowed.”

The dense residential area in southwest Houston has 66,000 apartment units, and CoStar estimates 30 percent of those will be impacted.

The rising waters also overflowed into Houston’s River Oaks, where its wealthiest residents reside in luxurious mansions.

It also affected retail and hotel properties.

In a speech to Memphis hotel owners, Jay Freitag of STR warned this is just the beginning as mold means a redo for all interiors.

“You basically have to rip out everything down to the studs and rebuild everything,” he said, adding, “Where are you going to find people [to do repair work] if they can’t live in the city?”

As first reported by Hotel-Online, Frietag says conventions heading to Houston must also change locations, with other Southern cities the likely benefactors.