A Portland developer has begun construction on 28 apartment units inside the Clapp Memorial Building at 443 Congress St. in Portland, including four units that will meet the city’s requirement for affordable housing.

Northland is building eight two-bedroom apartments, sixteen one-bedroom apartments, and four studio units on the former office building’s upper floors. Two commercial tenants on the first floor, the Portland Regional Chamber of Commerce and Planned Parenthood, both have long-term leases and will remain.

Northland is the first developer to include affordable apartment units under Portland’s relatively new requirement, city spokeswoman Jessica Grondin said. Developer Chip Newell’s 26-unit Luminato Condominium project on Newbury Street was the first condo project to include affordable units under the ordinance, she said.

The Portland City Council voted in October 2015 to require a portion of housing units in new developments to be affordable to middle-income earners.

The rule requires that 10 percent of the housing units in new developments of 10 units or more be affordable to those earning 100 percent to 120 percent of the area’s median income. However, developers can avoid the requirement by paying the city $100,000 for each required affordable unit they don’t build.

Northland said rents for its 443 Congress units will be “moderately priced” and will include heat, air conditioning, gas cooking, granite countertops and in-unit washer/dryers. The building will undergo a National Park Service historic renovation, with new historic replica windows and a renovation of the upper four floors.

The company said it expects the apartments to be ready for occupancy in January.