When residents walk into Hong Lok House in Chinatown, they enter a brand-new apartment building through one of the oldest doorways in Boston.

There are several unusual things about the $37 million Hong Lok redevelopment project, which created 74 new apartments for low-income senior citizens in one of the hottest neighborhoods in the city. One of those things is the façade: three storefronts that date to the 1800s, tacked on to a new building.

It was painstaking work, said Andrea Gilmore, director of Newton-based Building Conservation Associates, which oversaw the façade restoration for the developer, Rogerson Communities. The storefronts had to be separated from the buildings behind them, which were too decrepit to save. Two were deconstructed piece by piece — hundreds of pieces in all — loaded on trucks, and refurbished off-site. The third — five stories of brownstone, sandstone, and granite — was held in place by a steel frame while the building went up behind it.

After the building rose, the pieces were trucked back and reassembled. The work did drive up the project’s cost, though a city program for facade repair funded some of it. And it helped build support for the development among preservationists.

Yet it’s not exactly the same. The new building, after all, is not quite like what was there before. Windows are in different spots. Floors sit at one level all the way through, instead of at different levels in each building. That meant the reconstructed facades needed a nip here, some extra filling there, to make everything fit just right.

“This is not like building new,’’ Gilmore said. “It’s really­ putting together a jigsaw puzzle of building materials of different ages and condition and performance. It’s one of the most complicated projects we’ve ever done.’’

It preserves a historic streetscape though, she noted. The apartments behind the façade house 74 seniors in a place where affordable apartments are growing scarce. And those newly polished doorways will continue to be among the oldest in Boston.

“They’ll be here for hundreds of years,’’ said Jamie Seagle, Rogerson’s president.

TIM LOGAN

Tim Logan can be reached at tim.logan@globe.com.