The roof of Darling Washington’s three-decker on Meetinghouse Hill has a leak. And through a new Department of Neighborhood Development program focusing on that particular kind of housing stock, the single homeowner will receive the financing needed to patch it.

“I know I couldn’t do it myself and they’re going to do more than just my roof,” she said, days after standing with Mayor Thomas Menino and other city officials and brandishing a membership card that comes with the program. An annual housing expo at the Perkins Community Center served as a launch pad for the $3 million effort.

Washington’s three-decker is one of 9,000 across the city.

“That housing stock is so unique to Boston,” Menino said, adding that they were popular with immigrants and mill workers when they started being built 125 years ago.

“No other city has three-deckers like we do,” said Jim Hunt III, Menino’s chief of environmental and energy services.

Up to $30,000 in loans and grants will be available to three-decker owners for renovations, with a third of the money required to go towards exterior repairs. Around 75 three-deckers would be rehabbed if every applicant goes for the same amount, but city officials say applications will likely vary in financial need.

Owners with over $20,000 in repairs will receive free technical assistance on bidding and selecting a contractor, according to DND.

Program applicants to the program will also receive a free energy assessment.

Separately, up to $20,000 in down-payment assistance will be available for prospective homeowners looking to buy a three-decker – three apartments stacked on top of one another. Citizens Bank is making available $17 million in financing for potential homeowners and a 1 percent home improvement loan of up to $10,000 in repairs for homeowners to match city funds, according to bank president Jerry Sargent.

The Norfolk Hardware store, which sits on the Dorchester-Mattapan line, will also provide discounts to members of the DND three-decker program, according to Ben Rosen, its owner.

Washington, a South End native who works in human resources at a state agency and has owned her Robinson St. three-decker since 1997, will likely use up the money repairing front porches, the roof, the decks and shingle siding. If there’s money left over, she’s hoping to change her red door to a forest green color, Washington added.

She has two other public-subsidized occupants in the building, which sits on a street lined with three-deckers.

The “3D” program is the city’s latest attempt to preserve the distinctive buildings. In 2002, Menino launched “Three-Decker Plus.”

According to a Reporter article at the time, the initiative provided $20,000 to help purchase a three-decker, as well as closing cost assistance from the city and FleetBoston, which provided a $20 million commitment. FleetBoston has since been absorbed into Bank of America.

Dating back to 1978, the city has promoted three-deckers, referring to them instead as “triple-deckers.”

“Buying a triple decker can be relatively easy and make economic sense,” one brochure said. “The purchase price of a well-maintained triple-decker in Boston ranges from $15,000 to over $50,000, depending on location, rental income, amount of land, apartment size and other features.”

More information on the new program is available at cityofboston.gov/3D.