The high demand for slots in the city ‘s independent schools is spurring dozens of private academies to embark on major expansion and capital improvement projects.

Thanks to millions of dollars of city financing, the Chapin School is adding two additional floors to its existing East End Avenue building, the Studio School on West 95th Street purchased two adjoining brownstones for its elementary and middle school students, and the Gillen Brewer School, which serves children with special needs, is acquiring a new facility that can accommodate 80% more students.

Now that more and larger families are choosing to stay in the city rather than move with their young children to Scarsdale, Stamford, or other suburban communities, school administrators say they feel increasingly confident about filling their seats and bringing in enough tuition dollars to finance large capital projects.

“It used to be very rare to have a family with three children in an independent school. Now three is very, very common,” the school head at Grace Church School in Greenwich Village, George Davison, said. “As a result, we’re fairly comfortable with the notion that we’ll have enough enrollment that we won’t be put in a position that we can’t pay back the loan. It makes you say, ‘I know we can do this.'”

The Grace Church School, a pre-kindergarten through eighth-grade academy, recently purchased and renovated nine buildings on East 10th Street and put up a new gymnasium for its 400-plus students using $20 million in tax-exempt bonds issued by the New York City Industrial Development Agency, which is administered by the city’s Economic Development Corporation.

Nonprofit private schools meeting certain requirements are eligible for “triple tax-exempt bonds,” a financing option by which academies can secure lower interest rates on borrowed funds and pay off the money over a longer period of time than with traditional bank loans. Among other eligibility requirements, schools must be certified by the New York Board of Regents, and if their tuition or assets exceeds $20,000 a student, they must provide at least half-tuition scholarships to at least 10% of their pupils.

While the agency has been granting financing to nonprofit schools, other not-for-profit groups, and small for-profit businesses for about 30 years, private schools have been taking advantage of these programs more in recent years.

“We’ve grown, and we wanted a space of our own,” the head of school at the Studio School, Janet Rotter, said, noting that there are about 20 names on the school’s waiting list.

Ms. Rotter said enrollment at the school could grow to 150 from 120 thanks to its new facility, financed in large part by $8.8 million in tax-exempt bonds issued by the agency. The new facility, slated to be completed by September, includes art, dance, and music studios, a “state-of-the-art” science laboratory, and a rooftop garden.

Nonprofit institutions often have difficulty securing bank loans at reasonable rates, Ms. Rotter said, so the agency funding becomes “invaluable.”

The bonds are also available to religious schools — recent program beneficiaries include Yeshiva Har Torah in Little Neck, the Hannah Senesh Community Day School in Carroll Gardens, and Bais Sarah in Boro Park, all Jewish schools — though the city funding must be earmarked for capital improvements related to schools’ nonreligious curricula.

The Brooklyn Heights Montessori School, the Reece School on the Upper East Side, City and Country School in Greenwich Village, and Trey Whitfield School in East New York are also recent agency bond recipients, according to the Economic Development Corporation.

“Not-for-profit private schools serve a vital purpose in New York City,” the executive director of the city’s Industrial Development Agency, Kei Hayashi, said in a statement to The New York Sun. “NYCIDA assists educational intuitions throughout New York City as a way to lessen the burden on public schools and create new opportunities for city students, while better serving their students by helping schools improve their facilities.”

Last year, the city’s Industrial Development Agency financed 50 capital improvement projects, which spurred some $2.6 billion in private investment, according to statistics provided by the Economic Development Corporation.