In its first 10 years in effect, a state law meant to preserve affordable housing in Massachusetts has protected almost 20,000 units but one national advocate said Wednesday that preservation alone will not be enough to meet the demand for affordable housing.

To mark a decade of a state law known as Chapter 40T, the Community Economic Development Assistance Corp. released its latest research on the impact the law has had and brought together a group of advocates to discuss the past and future of affordable housing retention.

“Chapter 40T has been a big success, contributing to the preservation of almost 20,000 units while only losing 204,” Bill Brauner, director of housing preservation and policy at CEDAC, said.

Chapter 40T was enacted late in 2009 and applies to properties that are funded through 16 specific housing programs, like the federal Section 8 program and state rental vouchers. When a property’s affordable housing restriction is set to expire – often through a mortgage maturity, contract expiration or the end of a tax credit use restriction, Brauner said – the law requires notices of the expiration be sent to tenants and local officials, and provides the state Department of Housing and Community Development the right of first offer and the right of first refusal on the property.

“Upon receiving an offer to sell, DHCD will then designate a pre-qualified preservation buyer to act on behalf of the state and, for 90 days after the offer to sell notice is received, the owner cannot accept any offer, except from the designee,” Brauner said. “However, the owner is not required to accept the offer.”

Though the non-binding nature of the right of first offer may seem “toothless,” Brauner said that 10 of the 14 properties that have been purchased to date by DHCD designees have been purchased with the right of first offer.

The law also offers tenant protections. For three years after a termination, rents cannot be increased by more than the Consumer Price Index plus 3 percent for low-income residents who do not receive enhanced vouchers, Brauner said.

Priya Jayachandran, president of National Housing Trust, said she considers Chapter 40T “a model law for housing preservation” and that her organization often shares the law with other states that seek its expertise. But she argued that housing advocates should begin to take a broader view of housing and housing preservation.

Many organizations have long focused on preserving subsidized affordable housing units, as Chapter 40T does, but Jayachandran said “the vast majority of affordable housing is, in fact, in unsubsidized units that fall under the radar” and that the scope of preservation should be expanded to also capture those units.

She also made the case for housing advocates to join forces with environmental activists focused on stemming the tide of climate change to promote affordable housing preservation.

“I think the more that we can link housing preservation to infrastructure and climate change, to share that the energy burden from new construction – from all aspects of that, from the materials cost, from the transportation of those new materials, from the construction costs – the whole process is much more energy consumptive than is housing preservation,” Jayachandran said.

But she also acknowledged that preservation alone is not enough.

“Notwithstanding what I just said about energy consumption, the reality is that we need to be preserving units and creating units at the same time,” Jayachandran said. “When NHT was created in 1990 to focus on preservation, it was because housing preservation was the most pressing affordable housing issue of our time. It continues to be pressing, but the reality today is that even if we did preserve every one of our units, it’s not enough. We have simply not built up over the past 30 years the way we should have.”

Gov. Charlie Baker has been pushing since 2017 for lawmakers to agree to a zoning reform measure intended to spur housing production, and the governor has pointed to it again as one of the items he would like to see the legislature pass before the session ends early next month.

The House and Senate each included Baker’s long-sought zoning reforms in the differing versions of the economic development bill that has been under private House-Senate negotiations since July 30.