ARTICLE 25A, COASTAL FLOOD RESILIENCE OVERLAY DISTRICT
September 15, 2021
WRITTEN BY YVE TORRIE, DIRECTOR OF CLIMATE, ENERGY, & RESILIENCE
On Monday, September 13th, the Boston Planning and Development Agency (BPDA)’s Board approved regulations to establish a Coastal Flood Resilience Overlay District (CFROD) to ensure that certain new or substantially renovated buildings in the city’s most flood-prone neighborhoods can withstand risings seas and storm surges. The CFROD, also referred to as Article 25A, would apply the BPDA’s Coastal Flood Resilience Guidelines for projects subject to Article 80 Large and Small Project Review. In terms of process next steps, it is expected that at the October 13, 2021, Boston Zoning Commission hearing, the BPDA Director will petition the Commission to adopt Article 25A and the overlay district map and the approval will ultimately be granted.
Based upon feedback from A Better City, other stakeholders, and the public, Article 25A was updated and a revised version posted on August 23, 2021. The updated markup showed that consideration had been given to A Better City’s comments about below grade parking and modeling data clarification. A Better City submitted comments on the draft Coastal Flood Resilience Overlay District on February 12, 2021, to make the following recommendations:
- The resilience review component of Article 80, not the Board of Appeals, is the more appropriate process for determining that all uses proposed within the CFROD are designed to address projected coastal flood risks.
- Below grade parking that includes parking accessory to non-residential uses should be amended to include residential and mixed-uses as well.
- Modeling data used in the determination of the CFROD map should be amended to clarify the rationale for the selection of current datasets as well as the cadence for the update of the datasets and the resulting CFROD map.
- Language clarification and guidance should be provided to ensure that an individual property, in the process of enhancing an individual parcel or project, is not worsening risk on adjacent parcels.
As part of the 2016 Climate Ready Boston plan, Climate Ready Boston directed the BPDA to develop a set of design guidelines and a zoning overlay district to promote coastal flood resilience in vulnerable areas of the City. In 2019, the BPDA developed Coastal Flood Resilience Design Guidelines for new construction and building retrofits, aimed at assisting property owners in understanding their vulnerability to current and future flood events while providing a best practices toolkit for flood resistant design measures. The Design Guidelines were adopted by the BPDA on September 12, 2019.
Since then, the BPDA has been developing a Coastal Flood Resilience Zoning Overlay District, Article 25A, as part of the Boston Zoning Code. The Zoning Overlay and zoning map relates to areas of the City anticipated to be inundated by a major storm event (known as a 1% chance of flood event) in 2070 with 40-inches of sea level rise, which is within the usable life of most buildings currently undergoing BPDA review. The 40-inch inundation area is already integrated into the BPDA Zoning Viewer and represents flood extents and flood levels as the Sea Level Rise Base Flood Elevations (“SLR-BFE”).
The flood extents and elevations have been modeled through the Boston Harbor Flood Risk Model, which has been used by the City and Commonwealth of Massachusetts to evaluate future flood risks. Within the Zoning Overlay there are new definitions and standards for building dimensions and uses to facilitate flood resilient design for new projects and building retrofits. Specific provisions include:
- Sea Level Rise Design Flood Elevation (SLR-DFE): Establishes a minimum elevation for the lowest floor for residential uses and the flood-proofing elevation for non-residential uses. It is comprised of the Sea Level Rise Base Flood Elevation (SLR-BFE), with one or two feet of freeboard, or margin of safety, based upon sensitivity of use.
- Limitations on Use Below the Sea Level Rise Design Flood Elevation: For health and safety purposes, uses beneath the SLR DFE are limited to access or vertical circulation structures, flood prevention measures, storage, and parking.
- Building Height: To promote the elevation of occupiable space, projects undergoing Resilience Review will have their height measured from two feet above the Sea Level Rise Base Flood Elevation (SLR-BFE), rather than at grade, which is what current zoning requires.
- Building Setbacks: Projects will have allowances to extend into side yard, rear yard, and front yard setbacks for structures needed for vertical circulation, such as stairs or ramps to get from surrounding grade to a higher first floor elevation. There are also allowances for side yard and rear yard encroachments for new structures to house mechanical systems to ensure they are not located in basements or beneath the Sea Level Rise Design Flood Elevation (SLR-DFE).
- Lot Coverage & Required Open Space: The structures needed for vertical circulation and mechanical systems referenced above will be excluded from measurement of lot coverage and open space.
- Gross Square Floor Area: Will exclude structures needed for vertical circulation and areas devoted to flood protection measures.
The Design Guidelines will be administered with the Zoning Overlay through Resilience Review which will become a component of the Article 80 development review process.
For further information, please contact Yve Torrie.
