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High and Dry: Managing Multifamily Buildings in the Floodplain

Aug 13, 2020 | What's New

By H. Martin Koch, CFM, LEED Green Associate

According to National Multifamily Housing Council and U.S. Census Bureau data, nearly 390,000 new residential multifamily housing starts occurred in 2019. This is more than triple the number that occurred just a decade ago. While the COVID-19 public health emergency may result in changes to real estate development patterns, multifamily structures will likely remain a key source of dwelling units across the U.S., especially in major metro areas and communities home to large colleges. For instance, advances in building codes and fire-resistant materials have allowed for the growth in popularity of mid-rise wood-framed “podium buildings,” which often incorporate four to five residential stories above a concrete-framed commercial-use “podium” at the ground level.

multifamily apartment building

Multifamily structures bring unique rules and challenges. Photo by Canva.

To help floodplain managers address these trends, FEMA recently released FEMA P-2037 (Flood Mitigation Measures for Multi-Family Buildings). The topics covered by this publication correspond to issues that are relevant to building officials, urban planners, and real estate developers in today’s rapidly-changing urban landscapes. Please note that my suggestions are based on interpretation and experience, and do not necessarily represent an official position of my employer. For official guidance, floodplain administrators should contact their NFIP state coordinator or FEMA regional office.

One helpful focus area concerns ancillary residential uses. Many new apartment buildings compete for tenants by adding amenities such as package delivery lockers, fitness centers, and even bicycle repair and pet-washing stations. Since these functions often substitute for services provided by local businesses, permit applicants may assume that areas with these uses are considered nonresidential and eligible for dry floodproofing in A zones. However, as P-2037 clarifies, “From a floodplain management perspective, buildings with multiple dwelling units and ancillary use areas that support the dwelling units are not considered mixed-use buildings, so the entire building is considered residential.” [emphasis added]. Therefore, even components of a residential multifamily structure that do not serve as dwelling units must be elevated above the design flood elevation in the given community. “Electrical, heating, ventilation, plumbing, air conditioning, and other service equipment…” that serves residential uses must also be elevated.

Floodplain managers who are familiar with permitting new homes may be aware of the exception listed in 44 CFR 60.3(c)(5) that allows garages, crawlspaces, and other enclosures used only for parking of vehicles, access, or storage to be wet-floodproofed rather than elevated. The same applies to multifamily structures. P-2037 clarifies that “For the purposes of this publication, a lobby refers to a space designed to provide separation and control access between public spaces and commercial or residential spaces, including access to dwelling units. The term includes vestibules, foyers, and spaces or areas that provide access to elevators…. Lobbies with furniture, sitting areas, trash receptacles, or other contents or fixtures change the use of the area to something other than strictly building access. Tenant mailboxes, security desks, and tenant services would be considered uses other than building access.”

The fine distinction between access lobbies, which can be wet-floodproofed, and ancillary residential use areas, which must be elevated, means that a non-conversion agreement or covenant would be a good tool for local floodplain administrators to use in such scenarios. Floodplain administrators should also be sure to verify that elevators comply with all requirements of NFIP Technical Bulletin 4 (Elevator Installation for Buildings Located in Special Flood Hazard Areas in Accordance with the National Flood Insurance Program).

Another distinction that floodplain administrators should note when permitting multifamily structures is the greater level of regulatory flexibility afforded to mixed-use structures compared to those that are solely residential. P-2037 states that “When properly designed, constructed, and certified to be dry floodproofed, the lowest floor of a mixed-use building is allowed below the BFE; however, the lowest floor can only be used for non-residential purposes.” Additionally, “Lobbies that provide access to both commercial and residential spaces are allowed to be dry floodproofed…[however]…there [must be] separate building access for the residential spaces that is either wet floodproofed or elevated…”

To illustrate why this separate access point is required, imagine that a fire or other emergency occurs in the midst of an emerging flood event at a mixed-use building. If the commercial spaces had been closed in advance of the flood and shielded with waterproof barriers, then the evacuation routes through those spaces would no longer be a viable path of egress for occupants of the residential spaces. A separate wet-floodproofed access route provides a continuously-operational escape path for continuously-occupied residential areas of the structure.

Permit applicants can maximize the space available for generating revenue by choosing a mixed-use, rather than completely residential, design for a multifamily building in a flood hazard area. For instance, a resident-only fitness center or pet-washing facility would need to be elevated, while a commercial gym open to all paying members or a pet grooming business could be dry-floodproofed and located on the ground floor. The latter option would maximize the number of units available for lease in a height-restricted area, while ensuring that dwellings are securely elevated.

Another regulatory flexibility afforded to mixed-use structures compared to those that are solely residential is below-grade parking. P-2037 states that “…in Zone A, professionally designed buildings that have both commercial (non-residential) and residential uses may be designed with floodproofed below-grade parking garages.” Installing parking spaces in mixed-use buildings below grade further maximizes the number of levels that are available for commercial or residential tenants.

The American Planning Association’s Smart Growth principles for efficient and sustainable land development support “mixed-use development patterns” as a means to strengthen the economic and social fabric of neighborhoods. By leveraging their knowledge of NFIP regulatory requirements for multifamily structures in flood hazard areas, local floodplain managers can help developers choose pathways to compliance that build environmental and economic resilience.

H. Martin Koch, CFM, LEED Green Associate is an environmental protection specialist with the District of Columbia Department of Energy and Environment.

This article was published in the August issue of ASFPM’s News & Views. Read the entire issue here.

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