Wondering whether it's a Second Empire home? Just look at the roof.

Sometimes, parsing out which architectural style a home fits into feels like splitting hairs. But with Second Empire homes, it’s easy — just look at the roof.

“The number one feature of the Second Empire style that allows anyone to recognize it on any building is its distinctive roof,” said Peter Barr, a professor of art history at Adrian College who documents the architecture of Adrian, Michigan, for Adrian Architecture. “And the roof is called a ‘mansard roof,’ M-A-N-S-A-R-D.”

Adorned with flat tops and four sloping sides, mansards are a form of hipped roof. The distinctive feature means that mansard roofs cover their home’s top — often third — story. You might see a house that looks two stories tall, Barr said, but then you have an enormous roof that creates a whole third level.

The feature makes style discernment easy, because “if you see a roof like that, you’re 100% guaranteed you’re looking at a Second Empire house,” Barr said.

These homes also possess other distinctive traits and a legacy rooted in innovation.

Developed in mid-19th century Paris, Second Empire architecture gets its name from the French regime that began in 1852 under Louis-Napoleon Bonaparte, or Napoleon III.

Seeking to reconstruct the capital city in his image and to carve out a more easily controlled urban plan, Napoleon III charged Baron Haussmann with overhauling the city’s centuries-old quarters. In addition to clean water sources, wide boulevards and sewage networks, Haussmann implemented the distinctive Haussmannian architecture that still defines Paris, with its cream-colored buildings and silvery mansard roofs named for architect François Mansart. That's Mansart with a T.

As international travelers visited Paris for the Exposition Universelle in 1855 and 1867, the style became associated with innovation, Barr said. In addition to the latest technological marvels of the age, visitors “would have seen the brand-new, beautiful buildings being built in Paris with these mansard roofs,” Barr said. “It represented the height of modernity.”

Architects and builders seeking to capture that modern look brought the style stateside, with Washington, D.C.’s Renwick Gallery, a Second Empire-styled museum, as one of the first examples around 1861. Barr’s hometown of Adrian got its first Second Empire structure in 1867, he added, but the style is found across the United States in cultural, commercial and residential buildings completed before the style fell out of popularity toward the end of the century.

On the outside, original Second Empire homes generally boast intricately patterned slate shingles on their mansard roofs. Found in a variety of shapes and colors, these flat expanses are often punctuated by dormer windows, Barr said. The bump-out fenestrations pull light and ventilation into the third floor, ensuring that it is usable space.

Often, this space served as storage, as Victorian-era homeowners looked to stash away the increasing amount of mass-produced stuff they accumulated in an industrial economy. But some used their third-floor space for socializing: “There is a house here in Adrian called ‘The Sears House,’” Barr said, “and the third story is a ballroom.”

Under that hipped roofline, there’s also a good chance that you’re going to find carved brackets. Don’t let those brackets confuse you, Barr said: Although characteristic of Italianate architecture, if those brackets support a mansard roof, it’s still a Second Empire home.

Roof aside, Second Empire homes come in a range of materials, including brick and wood siding. In Paris, Barr noted, builders formed Second Empire buildings from limestone, but “Americans typically used whatever material was locally available,” he said. Barr’s hometown of Adrian had a notable brick factory as the style spread, so many of the town’s Second Empire residences were constructed with the material.

Although Second Empire homes may not hold the same modern cachet they evoked in the 19th century, they still capture hearts and imaginations.

From the streaming hit "Stranger Things" to Alfred Hitchcock classic "Psycho" and Edward Hopper paintings, "you have this image of a Second Empire home on a hill sitting along with crows flying around," Barr noted. Although a departure from the architecture's original link to modernity, "there is something connected to that kind of Halloween spirit."

Their mansard roofs alone hold a certain cultural cachet, with indie band Vampire Weekend using the element as a rarified motif in its 2007 song “Mansard Roof.”

Some people, Barr said, just “love the look of these homes” and are “seduced by their incredible curb appeal.”

Still, original Second Empire homes may need extensive work — their small kitchens often require an overhaul or addition, and maintaining a slate roof is notoriously expensive — and leaks may plague their flat roofs. For those reasons, some Second Empire homes have been stripped of their original detailing or subdivided into multiunit properties.

But the costs come with the valuable features associated with older homes: Second Empire structures often hold materials (think old-growth mahogany) and building techniques abandoned in modern architecture.

For Barr, these spacious, often symmetrical homes have an inherent grace.

“It feels grand when you go into these houses,” Barr said. “They’re just large, welcoming.”