At least two apartment projects in the works for central Dallas are different from almost a dozen other high-rise residential buildings under development in North Texas.

They include designated affordable-housing units reserved for lower-income residents.

One of those projects, on the eastern edge of the central business district downtown, will set aside more than 100 units for affordable housing.

Developer Jack Matthews — who built the Omni Dallas Hotel — is planning the mixed-income rental community as part of his redevelopment of the old Dallas High School site at Pearl and Bryan streets. The more-than-century-old school on the corner has already been converted into first-class office space.

Proposals for construction on the sites surrounding the school have included everything from more office and retail space to mid-rise apartments. Instead, Matthews and his partners are hoping to build a 16-story tower called 2400 Bryan with 230 apartments — 110 of which are reserved for residents earning between 30 percent and 60 percent of the area's median household income.

Matthews has already done one close-in workforce housing project, a 164-unit project in the Cedars neighborhood a few blocks south of downtown.

While developers have built thousands of new residential units in downtown Dallas in the past decade, a scant few have been priced for low and moderate-income renters. Only two downtown projects of significant size — the Lone Star Gas Lofts on St. Paul Street and the CityWalk@Akard — have been completed.

Together, they have fewer than 300 units.

"Our units stay full," said Larry Hamilton, whose firm did the Lone Star Gas project. "They actually have fewer downtown workers than I would have thought. But the demand is there."

Growing the base of affordable housing in the center city has been a longtime goal of city leaders.

Matthews plans to finance his project with a combination of low-income-housing tax credits, tax increment finance district funds and debt.

"2400 Bryan continues efforts by Matthews Southwest to develop quality workforce housing near transit facilities, and in close proximity to employment opportunities," Matthews said.

Hamilton said that while everyone agrees about demand, he doesn't foresee a surge in affordable-housing construction downtown.

"These are very hard to do," he said. "Downtown is as good a place as you can find for this. If you are trying to have an area with a blend of units, what better place than downtown."

The other apartment project with affordable housing is the one being planned for Dallas' Knox Street district. Developer Alliance Residential plans to build a 335-unit project on a 2-acre site at Cole and Armstrong avenues. At least 10 percent of units in that project, just across the street from the 17-story Highland Park Place office tower, would be designated as affordable-housing units.

With the average monthly rent on a new apartment in central Dallas running more than $1,800 a month, finding affordable rental housing is going to be a challenge without more projects that target workforce tenants.