Boston Pushes Flood Resilience with New Design Guidelines

The City of Boston is projecting 40 inches of sea-level rise by 2070, putting vast new swaths of the city within the 100-year flood plain. To prepare, the Boston Planning and Development Agency has recommended adopting a zoning overlay and released a set of design guidelines for projects residing within that zone.

If the zoning overlay is adopted, all new projects and large renovation projects (those that exceed 50% of the building value—or, alternatively, 50% of the building area) within the overlay would need to undergo resilience review before being permitted. This is required despite the fact that such projects may not currently be in a FEMA-designated flood zone. (FEMA floodplains, and FEMA’s model building standards, which many states adopt, do not take into account sea-level rise or climate change.)

The design guidelines would set the standard for the proposed resilience reviews. In fact, they are already serving as a reference in the development review process for projects larger than 50,000 square feet, according to the Boston Planning and Development Agency. But even more widely, the guidelines are becoming recognized as a useful articulation of coastal adaptation strategies.

Strategies plus other helpful considerations

The design guidelines outline the primary strategies for making buildings more resilient to sea level rise, including:

• elevating buildings (on open foundations, on filled subgrade space, or on fill)
• ensuring the structural integrity of building envelopes (wet floodproofing or dry floodproofing)
• safeguarding critical building systems (elevating equipment, protecting the motors and controls for elevators, and including backup water-management systems)

The guidelines also address the practical concerns that come with such strategies. The report demonstrates how to maintain access even when first floors are elevated, is upfront about cost and insurance considerations, and lists sustainability co-benefits that could be used to garner additional funding or support. One of the goals was to get audiences to “consider the public realm and how to improve it when advancing resilience best practices,” Jeff Geisinger, a co-author of the guidelines and director of sustainable design at Utile, told BuildingGreen.

Case studies by building type

The guidelines also illustrate how flood-resilient strategies might be applied to seven different building types commonly found in Boston:

• one- and two-family residential 
• triple decker
• attached townhouse
• pre-war mixed-use
• general industrial
• three-family residential (new construction)
• multi-family mixed-use (new construction)

For example, pre-war, mixed-use buildings are well suited to a raised interior floor, according to the guidelines. High ceilings make it possible to raise the floor without sacrificing the entire level. In contrast, many townhomes will likely need to convert basement or garden-level units to storage and build rooftop additions to recapture the lost square footage. That’s because many Boston townhomes—particularly in the South End—have units accessed through rear yards or back alleys that are up to six feet below the grade of the adjacent street, according to Nupoor Monani, director of urban design at Utile.

Sensitive to the fact that budgets may be limited—especially for renovating existing buildings—the guidelines detail both long-term strategies to increase resilience as well as short-term “incremental” strategies for each building type.

For one- and two-family residential buildings, the long-term strategies include protecting critical systems, elevating on an open foundation, re-purposing or re-locating ground floor use, and using flood-damage-resistant materials. Short-term, homeowners should move critical systems like mini-splits above the design flood elevation line, use flood-resistant materials below the line, and install backflow preventers and sump pumps. Low- and mid-rise residential make up a full half of the built square footage in the city, so such measures comprise a good portion of the work that needs to be done.

The importance of zoning

As for the overlay, zoning became important for two reasons, according to Monani. First, existing zoning may actually conflict with what is recommended for resilience. For example, height restrictions are generally counted from grade, essentially penalizing buildings that are elevated. Second, “complying with retrofit recommendations may trigger additional reviews, thereby deterring building owners from following through,” said Monani. An example might be expanding the building footprint to elevate mechanical systems. The building owner may only have funds for this one improvement, but the city may say the entire building has to be brought up to date with current zoning before additional square footage can be added. 

The proposed overlay could solve these problems. Height is defined by starting at sea-level rise flood elevations, according to Chris Busch, assistant deputy director of climate and environmental planning at Boston Planning and Development Agency. And expansions of structure for resilience retrofits are allowed as-of-right.  The exact provisions are still being discussed by the city, but the “Mayor has made this a priority,” according to Busch.