If you’re looking for a building that embodies what Somerville used to be—and what it’s becoming—15 Quincy Street fits the bill. The three-story, six-unit structure was built in 1895, and was originally a hotel for laborers working nearby.

Recently, the builder’s granddaughter sold it for more than $1.8 million to David Lilley, a developer and realtor. (He says she used that money to buy a home in Lynn, and to help her children purchase homes in Melrose and Tewksbury.)

Now, Lilley is rehabbing 15 Quincy Street for a very different clientele than the workers who originally occupied it.

“You’ll have a living room-dining room-kitchen combo, and then you’ll have three bedrooms, two baths, central air conditioning, rear decks,” Lilley says. “This is a very popular type of residential property right now.”

They won’t come cheap. Lilley expects the six units to sell for $650,000 or $700,000, and to rent for between $3400 and $3600 monthly—about ten times what they fetched 35 years ago, back when he first entered the real-estate business.

Construction is ongoing, but it’s easy to see the property’s appeal: there are high ceilings, bay windows, a roomy stairwell that boasts exquisitely detailed woodworking.

Another selling point: the future arrival of the Green Line extension, which will include includes a stop in Union Square, half a mile away.

Massachusetts recently decided to go ahead with the GLX, as it’s called, despite cost overruns that had threatened to kill the project. The new GLX plan is stripped down, and still needs final federal approval.

Still, Lilley says anticipation linked to the GLX is already boosting Somerville real-estate prices—and that its completion will push them even higher.

“They are pricing it in now, but once it’s here, that’ll really drive it,” he tells WGBH News. “This is something that’s been coming for over 25 years!”

Somerville’s housing market might already be the state’s hottest—the increase in single-family homes is nothing short of stunning—and if the Green Line has the effect Lilley anticipates, it won’t be good for everyone.

At a recent affordable-housing lottery at Somerville City Hall, a few dozen people anxiously watched as Danny LeBlanc, the CEO of the nonprofit Somerville Community Corporation, called out numbers linked to applications for a new development at 181 Washington Street in Union Square.

The anxiety in the room was palpable, and the odds were dauntingly long: just 35 units are being built—and 3400 people have applied.

Among them: Sonya Fuentes, a Somerville single mom who says she simply can’t afford to pay market rate.

“It would be too expensive,” Fuentes says. “Two bedrooms are about, like $2000 in Somerville.”

“I currently work at the airport, American Airlines,” she adds. “I get paid good, but not enough. So that’s why I’m here.”

It’s a far cry from the Somerville that LeBlanc moved to in 1976. He and three roommates shared a two-floor, four-bedroom apartment and split the rent. Their total cost: $250 a month.

Since then, LeBlanc has seen the Red Line extended Porter and Davis Squares, and watched housing prices climb across the city.

“This is not a perfect statement, but generally speaking, the western half of the city has gentrified more and sooner than the eastern half,” LeBlanc says. “So it’s kind of migrating east, we like to say.”

The Green Line Extension seems to be hastening that progression—but LeBlanc supports the project. For one thing, he argues, Somerville would be gentrifying regardless: an ever-increasing number of young, well-educated people want to live in cities, and there’s a massive lack of housing supply.

But he also considers the extension a matter of principle.

“Everybody ought to have good transportation in an urban area,” LeBlanc says. “And that especially means low and moderate income people who need it.

Of course, before they can take the train, they’ll need somewhere to live.

A recent change to Somerville’s inclusionary housing ordinance might help. Large new projects featuring 18 or more residences will have to set aside 20 percent of those units as affordable housing—a sharp increase from the existing set-aside rate of 12.5 percent.

But while that should alleviate some of the demand on the lower end of the market, it’s likely that Somerville will see more crowded, tense housing lotteries in the years to come.