Over the past few years, San Francisco’s Mission District has gone from laggard to leader when it comes to building affordable housing.

After a decade in which the Mission did not produce a single unit of affordable housing, the neighborhood skyline is dotted with construction cranes.

While there is a smattering of smaller market-rate projects under construction in the neighborhood, all of the tower cranes are for affordable developments catering to the sort of low-income families and seniors squeezed out of the gentrifying neighborhood over the past few years.

Five projects totaling 602 affordable units are under construction, and four more projects with 398 apartments are queued up behind those. Three tower cranes are visible from the gas station on the corner of 16th and Folsom streets: one at 490 South Van Ness Ave., one at 2060 Folsom St., and one at 1990 Folsom St. All are for developments where a family of four would have to earn less than $70,000 a year to qualify.

Supervisor Hillary Ronen, who pledged in 2016 to create 5,000 affordable units in the Mission in 10 years, said the neighborhood of 45,000 residents is nearly on track to reach her goal.

“My job is to be constantly hustling,” she said. “Every day we are looking for sites, looking for partners, looking for revenue sources. If we are not in a constant hustle to get every single unit of affordable housing, there is no way I’m going to make that 5,000 goal.”

The burst of construction activity comes after a 15-year period during which the Mission District’s Latino population fell by 8,000 residents, a 27% drop. Once one of the most affordable parts of the city, the Mission is now among the most expensive, with median one-bedroom rents of $3,585, according to Zumper.

Mission Housing Development Corp. Executive Director Sam Moss said that his organization, which owns 1,600 affordable units and is building new homes, has 10,000 people on its waiting list — many of them former Mission residents who have been forced to move to the Bayview, the Excelsior and out of the city altogether.

“Displacement has happened,” Moss said. “It is our intention to bring people back to the neighborhood where they built their lives.”

The Mission District’s first affordable project in a decade, a 94-unit senior complex, is opening this month at 1296 Shotwell St. The building will house 22 formerly homeless seniors, and some very-low-income seniors will pay just $300 a month for a one-bedroom, while others will pay $1,162 a month.

Demand for the building was overwhelming — 4,726 people applied, including 24 given preference because they had been evicted. The city’s neighborhood preference program allows nonprofit developers to set aside up to 40% of units for residents living in the same census tract as the building.

Mission Economic Development Agency, known as MEDA, and Chinatown Community Development Center developed the project.

Ronen credited Moss and MEDA Community development Director Karoleen Feng with jump-starting housing development at both nonprofits.

The spate of affordable projects arrives as the Mission has seen some market-rate projects languish. The district has 463 market-rate units that have been approved but not yet started construction. The largest potential project in the neighborhood, the so-called “Monster In The Mission,” near the 16th Street BART station, has been stalled for seven years as the property owner has clashed repeatedly with residents before even filing a formal application with the planning department.

Currently, only one major market-rate project is under construction — the 203-unit 2000 Bryant St., which has been branded Madelon, and is set to open in February.

“It’s the nicest apartment building I’ve ever built,” said Madelon developer Nick Podell.

Podell’s project, which critics called “the beast on Bryant,” faced significant opposition until he agreed to give a portion of the property to the city for affordable housing. The land donation will allow for 130 family-size apartments, expected to break ground in 2020.

Another controversial market-rate project, the 117-unit development at 2675 Folsom St., has stalled. The developer, Axis Development, won approvals in May 2017 after agreeing to make 27% of the units affordable. Rather than start construction, Axis put the property on the market in December, but it has not yet sold.

One market-rate developer, Lennar Urban, sold its 1515 South Van Ness Ave. site to the city for $18.5 million after a rancorous approval process. While Ronen called the deal “a great outcome” — it will produce 157 family-size affordable units — some housing advocates said that the market-rate project had become economically untenable because the builder conceded too many community benefits.

In addition to making 25% of the units affordable, the developer agreed to pay $1 million to a neighborhood group and lease commercial space at discounted rents.

Podell said construction costs are so high that he would not be able to make the Bryant Street project work today, even with two-bedroom apartments going for $5,000 a month. He was only able to pull it off because he bought the property in 2013, when land was a lot cheaper, and he purchased all the construction materials in 2016, when costs were lower.

“The whole system is broken. I don’t think the project would work with today’s costs, even with those obscene rents,” he said.

While delays stemming from political fights add to housing production costs, Ronen said she disagreed that activists had put so many demands on market-rate developers that the projects became infeasible.

“We haven’t denied a single market-rate project,” Ronen said. “We have asked for additional study, but they have all eventually been approved. Because the activists in the Mission are so outspoken, I feel like we get the rep that we are anti-housing, which is not true.”

But while Mission District anti-gentrification activists continue to fight market-rate projects, those projects help pay for affordable developments like 1296 Shotwell, a site that was donated to the city by the developer of the Vida condo development on Mission Street.

At 1296 Shotwell, the affordable project that some Bernal Heights residents opposed, construction is close to completion. On a recent morning, workers were scrambling to prepare the building for residents — testing elevators, filling planter boxes with dirt, screwing yellow metal sunscreens into the building’s exterior.

Susan Cervantes, who founded Mission-based public art nonprofit Precita Eyes Muralists, was working with four other artists to complete a mosaic lining the entrance to 1296 Shotwell. She pointed out a sun, a Caique bird, a fuchsia branch, a marigold flower, a Mission butterfly and a moon.

“It’s the seasons, the cycle of life,” Cervantes said. “I’m proud to be part of this project — being a senior myself.”

Those seniors will be moving in soon. Project manager Serena Li said the first 10 to 15 residents would arrive between Christmas and New Year’s.

“It will be a good Christmas gift for some people,” she said. “To have a home.”

J.K. Dineen is a San Francisco Chronicle staff writer. Email: jdineen@sfchronicle.com Twitter: @sfjkdineen