129 Portland St. in Boston's Bulfinch Triangle. Photo by Steve Adams | Banker & Tradesman Staff

Vacant office buildings in South End and the Bulfinch Triangle are joining the queue of planned housing conversions taking advantage of Boston’s offer of tax breaks.

The projects would create 51 new apartments in a pair of 19th-century buildings at 615 Albany St. and 179 Portland St. Both projects are proposed by Charlestown-based Construo Development.

In the South End, developers propose adding another story to the 5-story, 16,000-square-foot Albany Street building to create 24 apartments renting for an estimated $1,800 to $6,000. The project cost is estimated at $4.4 million, according to an application submitted to the Boston Planning & Development Agency.

Constru acquired the property in July 2023 for $3.4 million from Boston University, according to property records.

The estimated $5.6-million Bulfinch Triangle project would convert vacant office space into five apartments per floor ranging from studios to three-bedroom units, while retaining three ground-floor retail spaces. Estimated apartment rents range from $2,000 to $5,500. Property records list the current owner as Westport-based Olympia Group LP.

Under the requirements of the office-to-residential conversions program, the projects would include 17 percent income-restricted units and 3 percent for households with federal housing vouchers.

To date, developers have proposed 216 housing units at six properties totaling 173,000 square feet, according to the BPDA. Approved projects receive a 75 percent abatement on their property taxes for 29 years.

In March, the BPDA board approved Boston Pinnacle Properties’ 15-unit conversion plan for 281 Franklin St.