After years of planning, BPDA sets new rules for building in flood-prone parts of Boston

Would require large projects in many coastal neighborhoods to elevate ground floors and implement other protections

A flooded sidewalk off Congress Street in 2018, an increasingly common sight in Boston as the climate continues to warm.John Tlumacki

For years, environmental groups have criticized Boston’s approach to building in the face of rising sea levels, saying the city’s rules to make new construction more flood-resilient were essentially voluntary.

Not anymore.

On Monday, the Boston Planning & Development Agency board approved regulations that aim to ensure new or substantially renovated buildings in a vast swath of the city can withstand rising seas and storm surges.

The new requirements would apply well beyond the city’s federally designated flood plain. They cover more than 5,000 acres of land believed to be at risk from coastal flooding, including much of the Seaport, Chinatown, the South End, and East Boston, as well as parts of downtown, South Boston, Charlestown, the North End, and Dorchester.

City officials crafted this flood resilience “overlay district” in response to growing concerns about warming temperatures, more intense storms, and frequent flooding, and the risks they pose to the city as detailed in a 2016 report called Climate Ready Boston.

With the new rules, the BPDA is establishing a base-flood elevation point that assumes the potential for 40 inches of sea level rise in a severe storm. Occupiable space in residential buildings would need to be at least 2 feet above that point, said Chris Busch, assistant deputy director at the agency. Commercial buildings such as those with offices or labs could have usable space below that threshold, but it would need to be built with flood-proofing measures up to a foot above the threshold.

The elevation rules are based on projections for how bad coastal flooding could get in a severe storm over the next 50 years, with a 1 percent chance on average of such a storm occurring each year. The rules mostly apply to projects that are more than 20,000 square feet in size, but the minimum is 10,000 square feet in some areas closest to the sea, Busch said.

Only a few building features would be allowed below the flood threshold in residential buildings, including parking and storage. The BPDA originally proposed banning parking in those areas for residential buildings; it dropped the idea after receiving criticism that such a restriction could lead to more above-ground parking or curb the amount of housing that could be built.

The BPDA has requested many of the resiliency designs for several years through a voluntary checklist for developers. That process left too much open to negotiation, according to Deanna Moran, director of environmental planning at Boston-based environmental advocacy group Conservation Law Foundation. In contrast, the new rules include specific mandates.

“It is a huge, really positive step,” Moran said. “They’re spot on with their elevation requirements. This is something we’ve really needed in Boston. . . . They’re also sending the signal to the real estate community that they’re not afraid to codify this stuff.”

The new rules grant some concessions to make it easier to build storm-resilient structures. They include a slight increase in height limits, for example, or property setback allowances to provide room to ensure mechanical systems are above the new flood threshold.

The rules need approval from the city’s zoning commission, which could come as soon as next month.

“This is an important milestone in a multiyear effort,” BPDA director Brian Golden said. “We’re wrestling with a serious challenge.”

Public sentiment has shifted significantly in the past decade in favor of resiliency requirements, said Alice Brown, chief of planning and policy at nonprofit Boston Harbor Now, particularly after the havoc caused by catastrophic storms such as Sandy in 2012. That storm caused billions of dollars worth of damage in New York City and was seen as a wake-up call for cities along the East Coast. Still, in Boston, at least, investors and developers kept building pricey office and condo towers across the Seaport and in other flood-prone areas of the city.

“It would have been great if this was done a decade ago, and a whole bunch of buildings built in the last decade were built to these standards,” Brown said.

One potential shortfall with the new rules, Brown said, is that they don’t fully address urban design issues that can arise when the first floor of a new building is much higher than the street or those of its neighbors. For example, Brown said, “if you don’t have a talented urban design team, you [could] get something that just feels like a wall.”

Another shortcoming that Moran pointed to: the new rules only deal with flooding from the ocean, as opposed to rainwater deluges like the ones seen from the remnants of Hurricane Ida a few weeks ago. Moran would have preferred to see limits on impervious surfaces to address rain-related floods. (The Boston Water and Sewer Commission is studying ways to cope with excessive storm water.)

In May, New York’s City Council approved a similar change to what Boston is considering for areas in that city threatened by coastal flooding, driven in part by the damage caused by Sandy.

“What Boston is doing is incredibly smart and forward looking, recognizing that with a changing climate, we have to change our regulations,” said Michael Marrella, director of waterfront and open space planning for New York. “Oftentimes, when we look at Boston in comparison to us, it’s thought of as a competition. We’re really not competing against each other but we’re racing against the clock, recognizing how quickly the climate is changing.”

Trade groups representing builders and developers had largely positive things to say about the Boston rules. Anastasia Nicolaou, vice president of policy and public affairs at NAIOP Massachusetts, said many developers already incorporate storm resiliency into their designs. The new rules, she said, ensure they have a predictable review process, one that applies to everyone.

Greg Vasil, chief executive of the Greater Boston Real Estate Board, said he hopes city regulators show some flexibility as new technology evolves to cope with rising seas. Developers, he said, are often more tuned into the need to fortify buildings than they get credit for.

“Nobody wants to build a building that’s going to be an albatross and destroyed by flooding, and nobody is going to want to finance a building like that,” Vasil said. “We know Boston’s a city built on fill. . . . You don’t have to be a rocket scientist to know you’re going to have flooding at some point.”