The first phase will include 28 villas with amenities such as two-car garages, lofts and vaulted ceilings.
Work will begin May 6, with construction on phase one scheduled to be completed next summer, said David Riegsecker, vice president of corporate development.
"It will take eight to 10 years to develop, driven by the market," Riegsecker said. "We will build them as fast as we can sell them."
Carol Fries, vice president of marketing and development, said it is prudent for Menno Haven to begin building now.
"We know there is a growing number of seniors. We are on the right track," Fries said, pointing out the number of people age 65 and older has grown from one in 25 at the beginning of the 20th century, to one in eight at the beginning of the 21st century and is predicted to soar to one in four by 2050.
"We are facing a tremendous age wave," she said.
State Rep. Jeff Coy, D-Franklin, whose grandmother and uncle spent their final months at Menno Haven, called the plan "forward-thinking."
Citing statistics on the aging population in Franklin County, which had a 16 percent increase in residents age 65 and older between 1990 and 2000, Coy attributed the growth to "good health care, new innovative medicines, state government attention to seniors and the fact Pennsylvania does not tax retirement income."
The expansion is part of a nearly $60 million 10-year plan that includes a residential Alzheimer's facility at Menno Village and two community centers.
Menno Haven was founded in 1964 by two local Mennonite businessmen as a 60-bed nursing home on Scotland Avenue.
Since then, it has grown to a full-service continuing care facility that includes independent living, assisted living, skilled and nursing care at its Menno Village campus and Penn Hall, on Philadelphia Avenue in Chambersburg.
Access to 24-hour emergency response and maintenance-free living are what attract most residents to continuing care facilities like Menno Haven, Fries said.
Residents as young as age 60 purchase a life-lease, which provides the "umbrella of security" for emergency response and guaranteed access to whatever level of care they will need in the future, she said.
The Northfield apartment building and villas will join a combined 128 residential apartments and 359 cottages at Menno Village and Penn Hall.
In addition, Menno Village has 78 assisted living units and 173 nursing beds, while Penn Hall has 66 assisted living units and 60 nursing beds.