NEW MANSIONS LOOM OVER TINY KEY BISCAYNE

The lime green house has three bedrooms and one bath, 1,102 square feet in all. Its land-locked lot covers 77 feet by 100 feet. There is no garage.

The concrete-block home looks much like it did when the prolific Mackle brothers built it in 1950, when it would have fetched about $10,000.

The house is ordinary in all respects, except for that basic tenet of real estate: location; location; location. It’s in Key Biscayne. And it sold in March for $1.48 million.

Somebody call the authorities: Key Biscayne is on fire.

The Mackle house at 544 Ridgewood Rd. survived Hurricane Donna in 1960, Betsy in 1965 and Andrew in 1992. But it won’t survive the bulldozer that is almost certainly headed its way amid the latest boom.

“It’s a tear-down,” said John Paul Rosser, the listing agent for the seller. “I’m told the buyers want to build a new house — a spec house.”

Key Biscayne, a perennial retreat for the rich and powerful, wasn’t immune to the devastating housing crash. But like other luxury spots around Miami, it bounced back sooner and stronger than most of the region.

The longtime magnet for Venezuelans, Argentines, Colombians and Europeans is more international than ever. And while it historically welcomed a mix of wealthy and middle-class residents, home prices are effectively banning newcomers of moderate means.

For 2013, the median price for a single-family home in Key Biscayne, which is ZIP 33149, was $2,072,500, approaching its frothy 2008 peak of $2.2 million, according to an analysis by the Miami Herald and the Florida Center for Investigative Reporting. Many properties are going for record highs.

“The old knock-down Mackle houses sold for up to $1.4 million during the boom. Then we hit the skids, like everyone, and they were $850,000 or $800,000,” said Joan McCaughan, a longtime Key Biscayne resident and Realtor at Coldwell Banker. “Now you can’t find anything under $1.5 million.”

WALTER MICHOT / MIAMI HERALD STAFF

‘A THROWBACK PLACE’

Nostalgia is pivotal to the allure of Key Biscayne. “This place is a throwback place,” McCaughan said. “You can walk around at 2 or 3 in the morning, and nothing will happen to you.”

McCaughan’s father, Jim McCaughan, was a mortgage broker who helped the Mackles obtain financing to develop Key Biscayne. The boom has been great for her business, but she acknowledges the change sometimes makes her sad.

While many South Florida municipalities have struggled over budgets constrained by weak property tax revenue, Key Biscayne’s taxable property value jumped 6.46 percent last year to $6.15 billion. The bulk of that growth — 5.84 percent — came from the increased value of existing property, before counting new construction. The village had a surplus, enabling it to pare back its tax rate for 2013.

“We’re in a very, very good way with our real estate and how it affects ad valorem taxes,” said John Gilbert, the village manager.

A long-running gentrification of the Key has hit high gear as imposing mansions spring up on most every block, triple or more the size of the modest, older homes they replace on the tiny island.

“This is the most activity I’ve ever seen,” said Jud Kurlancheek, the director of building, planning and zoning, who has been with Key Biscayne 16 years.