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Review

Establishing a Sea Level Rise-Adjusted Design Flood Elevation for Buildings: A Comparative Study of Methods

by
Wendy Meguro
1,2,*,†,
Josephine I. Briones
1,†,
Eric Teeples
1 and
Charles H. Fletcher
3
1
School of Architecture, University of Hawaiʻi, Honolulu, HI 96822, USA
2
Sea Grant College Program, University of Hawaiʻi, Honolulu, HI 96822, USA
3
School of Ocean and Earth Science and Technology, University of Hawaiʻi, Honolulu, HI 96822, USA
*
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Water 2025, 17(16), 2376; https://doi.org/10.3390/w17162376
Submission received: 26 June 2025 / Revised: 29 July 2025 / Accepted: 29 July 2025 / Published: 11 August 2025
(This article belongs to the Special Issue Climate Risk Management, Sea Level Rise and Coastal Impacts)

Abstract

Coastal high tide flooding doubled in the U.S. between 2000 and 2022 and sea level rise (SLR) due to climate change will dramatically increase exposure and vulnerability to flooding in the future. However, standards for elevating buildings in flood hazard areas, such as base flood elevations set by the Federal Emergency Management Agency, are based on historical flood data and do not account for future SLR. To increase flood resilience in flood hazard areas, federal, state, regional, and municipal planning initiatives are developing guidance to increase elevation requirements for occupied spaces in buildings. However, methods to establish a flood elevation that specifically accounts for rising sea levels (or sea level rise-adjusted design flood elevation (SLR-DFE)) are not standardized. Many municipalities or designers lack clear guidance on developing or incorporating SLR-DFEs. This study compares guidance documents, policies, and methods for establishing an SLR-DFE. The authors found that the initiatives vary in author, water level measurement starting point, SLR scenario and timeframe, SLR adjustment, freeboard, design flood elevation, application (geography and building type), and whether it is required or recommended. The tables and graph compare the different initiatives, providing a useful summary for policymakers and practitioners to develop SLR-DFE standards.

1. Introduction

1.1. Existing Flood Hazards and Building Requirements

Since 2000, coastal high tide flooding, sometimes referred to as nuisance, sunny-day, or king tide flooding, has doubled in the U.S. [1] and and sea level rise (SLR) due to climate change will dramatically increase exposure and vulnerability to flooding in the future [2]. In 2000, where some regions saw an increase of over 400–1100% in 2020 in high tide flooding days [1]. In 2022, the national annual high tide flooding frequency reached four days on average; however, by 2050 with sea level rise, high tide flooding is likely to occur up to 85 days per year in some locations [1]. These events threaten up to 273,000 people and 171,000 properties in 32 major U.S. coastal cities [3]. The average service life of a building is 80 years [4] and potentially 130 years for U.S. residential housing stock [5], and climate change is driving sea level rise and more powerful storms [6]. Today’s building codes in coastal flood zones often do not require designs to withstand the flooding anticipated during the duration of the building’s useful life; however, coastal flooding caused devastation during multiple hurricanes over the last two decades, including Harvey and Irma in 2017 and Florence and Michael in 2018 [7].
In the U.S., approximately 30 million people (10% of the population) resided in a 100- and 500-year floodplain between 2011 and 2015 [8]. To avoid the cost of premium flood insurance rates and additional flood insurance requirements, the Federal Emergency Management Agency (FEMA) requires most building types in the floodplain to elevate or dry floodproof the first occupied level up to the base flood elevation (BFE) [9]. The BFE is the water-surface elevation of “a flood having a one percent chance of being equaled or exceeded in any given year” [10]. The BFE is determined from Flood Insurance Studies (FIS), which compile historic flood hazard data for specific areas [11]. The 1% annual chance floodplain or BFEs are depicted in Federal Insurance Rate Maps (FIRMs) and FIRMettes (a smaller, printable version of a FIRM) [12,13]. Because these studies are based on historical data, “[they] do not include the impact of future sea level rise, which clearly needs to be considered in the design of structures over the next several decades given recent National Oceanic and Atmospheric Administration (NOAA) sea level rise (SLR) projections” [7].
One approach to mitigate uncertain flood risk is to incorporate freeboard into building elevation requirements. Freeboard is “an additional amount of height above the base flood elevation used as a factor of safety” and is usually “expressed in feet above a flood level” [14]. Freeboard can provide further flood resilience by compensating for unknown flood factors, such as heavy rainfall or a shallow groundwater table. When additional height, like freeboard, is added to a BFE, the total is typically called a design flood elevation (DFE). According to FEMA, the DFE is a “regulatory flood elevation adopted by a local community” [15]. The DFE differs from a sea level rise-adjusted DFE (SLR-DFE), discussed in Section 1.3, which specifically attributes additional height to an SLR adjustment.

1.2. Sea Level Rise Scenarios and Impacts

The Global and Regional Sea Level Rise Scenarios for the United States [2] present decadal scenarios of global and regional sea level rise that include estimates of vertical land motion, for Low, Intermediate–Low, Intermediate, Intermediate–High, and High scenarios [16]. According to FEMA, “some states specify which future sea level rise scenarios should be used as a minimum” [15]. The initiatives compared in this study utilize the Global and Regional Sea Level Rise Scenarios for the United States [2] or other sources of SLR estimates while considering a community’s risk tolerance, to select a suitable SLR scenario and timeframe for policies addressing planning and building in coastal flood hazard areas.
One example illustrates use of the Global and Regional Sea Level Rise Scenarios for the United States [2], examination of SLR impacts, and development of building elevation guidance but not requirements. On Oʻahu, Hawaiʻi, the City and County of Honolulu (CCH) Climate Change Commission recommends, but does not require, using an Intermediate SLR scenario as the minimum for all planning and design, while considering the Intermediate–High SLR scenario for public projects and those with a low risk tolerance [17]. It recommends, but does not require, adding freeboard. SLR impacts in low-lying areas include direct marine inundation, storm-drain backflow, and groundwater inundation (GWI) [18]. According to Key Message 30.3 in the Fifth National Climate Assessment, the flood hazards associated with SLR in Hawaiʻi will negatively impact the built environment, harm numerous economic sectors, intensify loss of territory and exclusive economic zones, disrupt livelihoods, and result in expensive adaptation [19]. On the island of Oʻahu, 3.2 ft (0.98 m) of SLR would flood 3880 structures and displace 13,000 residents, leading to a USD 12.9 billion loss from impacted land and structures [20].
Impacts of SLR flooding should be assessed for the time period of the building’s useful life. The American Institute of Architects (AIA) notes that “decisions made in design and construction have lasting effects and are best made with a long-term perspective; this means projects that withstand the impacts of climate change, mitigate risk, and protect and enhance our existing resources” [21]. Strategies to mitigate flood damage “are generally driven by economic objectives, such as choosing courses of action where monetized discounted benefits exceed discounted costs (i.e., Benefit–Cost Analysis [BCA])” [22]. Although exceeding code requirements for flood and hurricane damage mitigation is shown to yield an average 6:1 BCA, saving USD 6 in disaster recovery for every one dollar spent [23], in the U.S., “homeowners rarely undertake damage mitigation voluntarily” [24]. While some countries, including the U.S., Belgium, Germany, and the UK are looking to increase managed retreat/realignment (MR) in coastal areas affected by SLR [25], in-place adaptation should also be evaluated, particularly in densely developed coastal communities.

1.3. The Need to Compare Methods to Establish Sea Level Rise-Adjusted DFEs

Methods to establish a flood elevation that specifically account for rising sea levels (or sea level rise-adjusted design flood elevation [SLR-DFE]) are not standardized. Municipalities are left to make their own projections for accounting for sea level rise for building elevation requirements, and a few cities (e.g., Boston and New York City) are consistently cited as flood regulation leaders [26]. By summarizing and comparing methods developed by initiatives on the federal to city level across the U.S., this research informs decision-making by policymakers and design teams as they develop their own SLR-DFEs.
The terms “DFE” and “SLR-DFE” are used differently across the initiatives studied. For this study, the SLR-DFE is defined as a DFE (a BFE plus freeboard or other elevation requirements) that specifically incorporates SLR. Similarly, New York City’s Climate Resiliency Design Guidelines define an SLR-DFE as, “the increased height of the base flood elevation due to sea level rise plus freeboard” [27].

2. Materials and Methods

2.1. Factors and Criteria for a Sea Level Rise-Adjusted Design Flood Elevation

The team summarized and compared each initiative’s approach to defining an SLR-DFE by categorizing factors including author/entity; the starting elevation for measurement; SLR scenario and timeframe; SLR adjustment; freeboard; design flood elevation; application; and whether it is required or recommended. The criteria were developed by the authors based on a review of SLR-DFE initiatives, and were not based on criteria from previous studies. The most often used or descriptive terms were selected for clarity and inclusiveness, given inconsistent vocabulary across initiatives. Section 2 defines each factor and Section 3 includes a summary of each factor in a table for each initiative. The Supplementary Materials includes a website link to a spreadsheet with all tables. Vocabulary is defined and illustrated in Figure 1.

2.1.1. Author/Entity

For each initiative, the author/entity wrote and published the guidance or requirements on building elevation for flood adaptation. The authors studied are government entities at various scales. The author/entity must acquire funding and expertise to create the guidance or requirements, and consider if and how to update and enforce them. This also provides insight into key partnerships and collaborations within a community to successfully develop an SLR-DFE.

2.1.2. Starting Point for Measuring SLR-DFEs

For each initiative, the team identified the starting point or elevation to which the SLR-adjustment, freeboard, and any additional factors are added. Understanding the starting elevation is important, as the total SLR-DFE height is relative to a datum that must be defined in order to be applied or compared to other methods.

2.1.3. SLR Scenario and Timeframe

This paper compares the initiatives’ sea-level rise scenario(s), sources of sea level rise data, and timeframe that are used to identify an SLR adjustment number, if any (described below). The Global and Regional Sea Level Rise Scenarios for the United States [2] provides SLR scenarios to 2150 by decade, which include estimates of vertical land motion. However, some of the initiatives compared in this paper pre-date that report and refer to other data sources. The timeframes in the initiatives studied vary but generally encompass the expected useful life/lifespan of a building.
On the federal level, there is an understanding that “[o]ne challenge of widespread implementation of multi-scenario methods for project evaluation is that decision metrics often reflect the risk tolerance of the decision maker(s)” [28]. The initiatives studied vary when defining “when” and “how much” sea level rise to plan for, perhaps reflecting different decision makers’ risk tolerances.

2.1.4. SLR Adjustment

An SLR adjustment(s) is a specific depth, amount, or height of water, described in this paper in feet and inches, and typically correlates to an SLR scenario at a local tide gauge for a specified timeframe. The datum used to measure SLR, such as mean high higher water (MHHW) [29], may differ from the datum used in FEMA flood insurance rate maps (FIRMs) for BFEs [30]. Other flood factors, such as land subsidence, were considered when determining an SLR-DFE.
All initiatives studied include land subsidence within the SLR amounts; however, Boston is the only initiative that explicitly quantifies the amount within an SLR adjustment. Land subsidence is “a gradual settling or sudden sinking of the Earth’s surface owing to subsurface movement of earth materials” [31]. “Coastal cities often experience sinking land (so-called land subsidence), whose compounding effect contributes to relative SLR, exacerbating coastal hazards and risks” [3].

2.1.5. Freeboard

FEMA defines freeboard as “an added margin of safety expressed in feet above a specific flood elevation”; usually the BFE. Freeboard can account for unknown factors, future development, and floods higher than the base flood [32]. Although SLR may be accommodated by using freeboard, in this paper it is discussed separately in the SLR Adjustment section to distinguish and quantify each factor (above).

2.1.6. Design Flood Elevations

The DFE is “[t]he elevation of the highest flood (generally the BFE, including freeboard) that a retrofitting method is designed to protect against”, [33] and is “[a] regulatory flood elevation adopted by a local community” [15]. It often exceeds FEMA’s requirement or standards, and may be required or recommended by individual municipalities. In addition to incorporating freeboard, the DFE can consider, “other adjustments to provide increased protection and minimize damage” [27]. FEMA’s definition does not necessarily include an SLR adjustment, but when a DFE specifically includes an SLR adjustment, other terms, such as sea level rise-adjusted design flood elevation (SLR-DFE), may be used, for instance, in the City of Boston’s guidelines (Section 3.1.3).

2.1.7. Application

For this study, the application describes the type of project, building use, and/or geographic area to which the initiative/guidance applies (e.g., a commercial or residential building, buildings used for emergency services, or buildings located in a specific coastal area/flood zone). Understanding the application provides insight into the intended occupants being considered and the value it serves to a community.

2.1.8. Requirement or Recommendation

While SLR planning has occurred for over a decade, specific recommendations and requirements, such as those in the initiatives studied, have rapidly developed within the last several years as new research and implementation continuously progress. Frequently, building elevation initiatives are recommended prior to adoption or requirement. All SLR-DFEs compared in this study are required to some degree, except the proposed code recommendations described for the Satellite Beach approach. This paper also describes how and when compliance with requirements is demonstrated.

2.2. Selection Criteria for Comparing Sea Level Rise-Adjusted Design Flood Elevations (SLR-DFE)

To assess the need for a comparison of approaches to establishing an SLR-DFE, the authors conducted a comprehensive search for peer-reviewed articles comparing state, regional, county, or municipal initiatives on this topic. Using the University of Hawaiʻi at Mānoa’s Library System A–Z Databases, approximatively 571 databases were searched using the following keywords between 16 August and 8 September 2023:
  • sea level rise [and] elevation [and] flood-* [and] adapt-* [and] design (35 results);
  • sea level rise design flood elevation (55 results);
  • design elevation sea level rise (168 results);
  • adaptation design flood levels sea level rise (179 results);
  • allowance flood damage sea level rise (4 results);
  • uncertainty sea level rise design buildings (30 results);
  • uncertain-* [and] adapt-* [and] design [and] sea level rise [and] build-* (26 results);
  • uncertain-* [and] adapt-* [and] design [and] sea level rise [and] built (8 results);
  • sea level rise building adaptations [and] elevat-* [and] flood (32 results);
  • building adaptations [and] sea level rise finished-floor (2 results); and
  • sea level rise finished-floor level (3 results).
Total Quantity of Results = 542 (* = varied suffixes).
After narrowing results based on the relevance of the articles’ titles and abstracts, the authors reviewed the most pertinent material and did not find any peer-reviewed articles comparing SLR-DFEs for buildings. Unable to find a peer-reviewed study, the authors broadened their investigation to identify U.S. locations that had developed building elevation guidance incorporating an SLR-DFE, SLR adjustments, or freeboard explicitly for SLR. A comprehensive, intentionally diverse list of seven initiatives were selected for comparison, ranging in scale (from federal to district) and approach:
  • ASCE (national-existing);
  • New York City, NY (municipal);
  • Boston, MA (municipal);
  • Kauaʻi, HI (county and district);
  • Florida (municipal, regional and state);
  • Rhode Island (state); and
  • Federal Flood Risk Management Standard (national-future).

2.3. Developing a Visual Comparison of SLR-DFEs

To visually compare each initiative, total elevations derived from multiple factors contributing to an SLR-DFE (or DFE) were graphed to scale. A legend with additional information is provided to explain the intricacies in each initiative that complicate direct comparison, such as varying starting points or elevations for measuring SLR-DFEs. Bar charts were chosen because they represent the additive nature of determining the total height of an SLR-DFE.

3. Relevant Initiatives

3.1. Summary of Approaches by Initiative (Locations/Guidance Studied)

3.1.1. FEMA and ASCE Guidance on Building Elevation (National)

FEMA recognizes that “FIRMs (Flood Insurance Rate Maps) reflect conditions at the time of the Flood Insurance Studies (FIS)”, yet they do not require elevation measures on a national level for future conditions [15]. Instead, they promote community scale adaptation: “owners, operators, planners, designers, and communities should consider how future conditions may influence flood characteristics over the life of a building when deciding how high to elevate the building or how high to specify flood protection elevations” [15].
FEMA assisted in developing several documents that provide recommendations for building elevations intended for adoption on a community scale; however, they are rarely required and, alone, do not meet the needs of all communities. One document outlines lessons learned from Hurricane Ian to “help guide repair and reconstruction efforts in designing new or retrofitting existing buildings to improve resiliency to future flood damage” [15]. The document recommends considering relative SLR at the very minimum, “equal to the historical rate” [15], but notes that this lacks data on future SLR.
In addition, FEMA’s Coastal Construction Manual “provides guidance for designing and constructing residential buildings in coastal areas that will be more resistant to the damaging effects of natural hazards” [34]. The document refers to the lowest floor elevation and freeboard requirements in the National Flood Insurance Program (NFIP), International Residential Code (IRC), International Building Code (IBC), and American Society of Civil Engineers’ (ASCE).
The IRC and IBC (through the ASCE Standard 24-14, Flood Resistant Design and Construction) incorporate a minimum amount of freeboard. ASCE Standard 24-14 meets or exceeds NFIP requirements, outlining minimum performance expectations for siting, designing, and constructing buildings in flood hazard areas [35]. The standard “provides minimum requirements for flood resistant design and construction of structures that are subject to building code requirements and that are located, in whole or in part, in Flood Hazard Areas”, and applies to “all new construction and substantial improvements” [36]. The ASCE categorizes buildings and structures into Flood Design Classes (1–4) based on their use or occupancy if damaged, ranging from “minimal risk to the public” (Class 1) to “essential facilities for emergency response and recovery” (Class 4) [35,36]. Most communities use FEMA flood insurance rate maps (FIRMs), but some communities may elect to adopt higher flood elevations (which ASCE calls the DFE) and show them on a map. A recent proposed update to the standard (ASCE 24-24 [37]), which has yet to be adopted, includes climate change considerations where “coastal floodplain calculations must now factor in future sea level change based on historic trends” [38]. Table 1 highlights the ASCE standard 24-14 approach.

3.1.2. New York City (Municipal)

New York City’s 2022 Climate Resiliency Design Guidelines (NYC Guidelines) are a leading example and “provide step-by-step instructions to go beyond building code and standards, which are informed with historic climate data, by also looking to specific, forward-looking climate data for use in the design of City facilities” [27]. The New York City Panel on Climate Change (NPCC) [39] provides regional climate change projections that inform the City’s climate resiliency policies [27].
Through a five-year pilot program required by Local Law 41 of 2021 [40], “23 City capital agencies will begin designing and constructing dozens of new projects using the standards in the NYC Climate Resiliency Design Guidelines” and “By 2026, all City projects must meet a stringent set of requirements that will certify their preparedness for extreme weather threats” [41]. The BFE, freeboard, and SLR adjustment (at the end of the building’s useful life) are combined to determine the SLR-DFE. For example, using Table 2, a building’s useful life ending in the 2050s requires a 16-inch (0.41 m) SLR adjustment. However, when the building’s end of useful life is in the 2080s, a 28-inch (0.71 m) SLR adjustment is required.
The NYC Guidelines apply to city facilities in the current or future 1% annual chance floodplain using the NYC Flood Hazard Mapper [42]. The future floodplain can be viewed for time ranges based on the building’s end of useful life. Facilities in a future floodplain use the nearest adjacent BFE [27].
Table 2. New York City (Municipal) DFE Approach 1.
Table 2. New York City (Municipal) DFE Approach 1.
Factor/CriteriaApproach
Author/EntityNYC Mayor’s Office of Climate and Environmental Justice
Starting Elevation MeasurementMeasured from FEMA BFE.(BFE Measured from NAVD 88; FEMA 1% Preliminary FIRM (PFIRM) (2015) or FIRM (2007).)
SLR Scenario and TimeframeMiddle of the 25th–75th percentile range projections from the NPCC. 2
SLR AdjustmentBased on end of useful building life (range):
  • 2020s (2020–2039): 0′–6″ (0.15 m)
  • 2050s (2040–2069): 1′–4″ (0.41 m)
  • 2080s (2070–2099): 2′–4″ (0.71 m)
  • 2100+: 3′–0″ (0.91 m)
Freeboard24″ (0.61 m)
Design Flood ElevationsSLR-DFE = BFE + SLR adjustment + Freeboard
ApplicationApplies to all city capital projects (new construction and substantial improvements) except coastal flood protection systems.
Applies to city critical and non-critical buildings (defined by NYC) within current or future 1% annual chance flood plain.
Requirement or RecommendationRequired for NYC capital projects (starting 2026)
Note(s): 1 Information from the 2022 NYC Climate Resiliency Design Guidelines [27]. 2 New York City Panel on Climate Change 2015 Report [43].

3.1.3. City of Boston (Municipal)

In Boston, Massachusetts, the Coastal Flood Resilience Design Guidelines [44] inform private development in becoming more resilient to coastal flooding. Developed by the Boston Planning and Development Agency (BPDA), the guidelines use the Boston Harbor Flood Risk Model (BH-FRM) to determine a localized and relevant SLR adjustment. The Massachusetts Department of Transportation developed the BH-FRM to incorporate SLR specifically for Boston Harbor. The model adopts SLR scenarios from data in the U.S. National Climate Assessment from 2012, acknowledging that the scenario was chosen, “despite the maximum of 1.2 m recently presented in the IPCC Fifth Assessment Report (AR5) WF1 material” [45].
A 2070 timeframe was selected because of the “long-lived nature of the city’s building stock and the hazards these building assets experience during their useful life” [43]. Boston’s Sea-Level Rise Base Flood Elevation (SLR-BFE) on their online BPDA Zoning Viewer is used for a future flood elevation based upon 3.2 feet (0.98 m) of sea level rise above 2013 tide levels, an additional 2.5 inches (0.06 m) to account for subsidence, and the 1% annual chance flood. Although land subsidence is typically incorporated into SLR estimates, Boston is the only initiative that clearly distinguishes the amount attributed to subsidence in their SLR-DFE. It is listed in the “SLR Adjustment” category shown in Table 3. In these guidelines, freeboard varies for existing (retrofits) versus planned (new construction) and is described as the distance between the SLR-BFE and SLR-adjusted DFE (SLR-DFE) [43].

3.1.4. Kauaʻi, Hawaiʻi (County and District)

The Kauaʻi County Land Use Regulations building code includes building design standards (Title IV County Planning and Land Development, Section 8–12.5 d) for elevation of buildings within their Sea Level Rise District (S-SLR) [49]. The S-SLR includes all lands within the County of Kauaʻi Sea Level Rise Constraint District subject to annual high wave flooding and passive flooding impacts projected by the Kauaʻi Sea Level Rise Constraint District Viewer (with 3.2 feet (0.98 m) of sea level rise anticipated to occur within this century).
The Kauaʻi County Planning and Land Development Ordinances (Comprehensive Zoning Ordinance Ch. 8–12.2 [49]) updates were originally spurred by the West Kauaʻi Community Plan [50]. In 2020, legislation added the Kauaʻi Special Treatment Coastal Edge (ST-CE) District (Ch. 8–11.2) and established a requirement for all projects within specified areas to acquire a use permit, which must be granted before a building permit for new construction or major renovation (Ch. 8–3.2) [51]. In 2023, the Kauaʻi Sea Level Rise District (S-SLR) was implemented, “to ensure that development within those applicable areas is constructed in a manner that safely mitigates impacts from coastal hazards, including but not limited to sea level rise, coastal erosion, high wave run-up, passive flooding, and an increased frequency and intensity of storms” [51]. This approach is summarized in Table 4.

3.1.5. Florida (State, Regional and Municipal)

Florida is an example where state, regional, and municipal guidance is provided. In general, state and regional guidance provides information on SLR scenarios, SLR maps and broad ideas for adaptation, whereas municipal guidance provides more specific building elevation requirements.
At the state level, the Florida Department of Environmental Protection (FDEP)’s Resilient Florida Program is part of a legislative effort to “ensure a coordinated approach to Florida’s coastal and inland resilience” and host online resources, such as statewide vulnerability assessments, mapping tools, and adaptation plans, as well as to provide grants to municipalities for adaptation, mitigation planning, and projects [53]. Published by the Resilient Florida Program, the Florida Statewide Vulnerability Assessment “identifies inland and coastal infrastructure, geographic areas and communities in Florida most vulnerable to flooding and sea level rise and the associated risks” [54]. In addition, Florida requires state-financed construction projects within areas at risk due to sea level rise to complete a sea-level impact projection (SLIP) study, effective 1 July 2024 [55]. The SLIP reports do not include freeboard requirements; however, they use “NOAA sea level projections, FEMA coastal storm surge events, and associated wave heights” to assess the flood risk at a project site and provide information, including “Potential Beneficial Adaptation Strategies”, which may suggest site-specific strategies to mitigate flooding, such as to “Build on Partially Elevated Areas” [56]. The 2024 SLIP Study Standards [57] outline requirements, including “sea level rise expected over 50 years or the expected life of the potentially at-risk structure or infrastructure, whichever is less”, and “at a minimum, include the highest of the sea level rise projections required by Section 380.093(3)(d)3.b., F.S.” [58].
Prior communication from 2021 specified using the 2017 NOAA Intermediate–High SLR scenario [59]. Currently, the Florida Statute 380.093(3)(b), referenced above, states that vulnerability assessments must be developed to consider, at a minimum, the 2022 NOAA intermediate–low and intermediate SLR scenarios or the statewide SLR projections [58]. The establishment of SLIP studies is the culmination of over a decade-long process, pushed forward by the 2015 Peril of Flood legislation (SB 1094) and included pilot projects run by cities across the state to explore how to adapt to SLR [60,61]. The state-level initiative prompted the creation of new regional and municipal guidelines based on individual community needs. Municipal examples from the cities of Miami Beach and Satellite Beach, which are located on barrier islands, are summarized in the text and tables below.
On a regional level, the Southeast Florida Regional Climate Compact, a partnership between Broward, Miami-Dade, Monroe, and Palm Beach Counties, to work collaboratively to reduce regional GHG emissions, implement adaptation strategies, and build climate resilience across the Southeast Florida region [62], has led a call to action in climate change planning that “solidified a coordinated, regional response” [63]. Outlined in their 2019 Unified Sea Level Rise Projection Southeast Florida document, the SLR scenarios used are the “median” curve of the IPCC Fifth Assessment Report (AR5) RCP 8.5 Scenario [64] and the NOAA 2017 Intermediate–High and High scenarios [63,65]. The document also provides guidance on the appropriate application of the scenarios.
On the municipal level, the city of Miami Beach (included in the Compact above) adopted its own additional requirements (Table 5). In 2023, Miami Beach updated its previous zoning code and ordinances (Land Development Regulations) to the Resiliency Code [66] “to set design standards that better protect the City against flooding, sea level rise, wind damage, and extreme heat” [67]. As stated in the Miami Beach Ordinance No. 2016-4009, regarding freeboard, “all new construction and substantial improvements to existing construction shall meet the minimum freeboard requirement and may exceed the minimum freeboard requirement up to the maximum freeboard without such height counting against the maximum height for construction in the applicable zoning district” [68]. To comply with the older (2021) version of the Resilient Florida Program, the City of Miami Beach SLR Vulnerability Assessment Report plans for the NOAA 2017 Intermediate–Low and Intermediate–High SLR scenarios, while adding the High scenario into their study to “potentially be used for developing adaptation strategies for critical infrastructure” [69]. The draft 2025 Miami Beach Sea Level Rise Adaptation Plan [70] acknowledges the existing freeboard ordinance (2016-4009 [71]) but proposes incorporating NOAA’s 2017 [65] SLR scenarios into finish floor elevations (FFE) to enhance flood protection, particularly for critical facilities. The Miami Beach Resiliency Code portions relating to building elevation are summarized in Table 5.
Outside of the regional Compact, the small city of Satellite Beach established what is known in Florida as an Adaptation Action Area (AAA) and provides local guidance, summarized in Table 6. The City promotes managed retreat within this area and implemented a coastal construction line (CCL), an element of Florida’s coastal management program that “regulates structures and activities that can cause beach erosion, destabilize dunes, damage upland properties or interfere with public access” and applies to “an area of jurisdiction in which special siting and design criteria are applied for construction and related activities” [72]. Their design standards require all habitable space and the lowest floor of residential projects to elevate “above the dune vegetation on stilts/pilings to a minimum of three feet (0.91 m) above the BFE” [73]. In addition, any project granted a variance for being less than 15 feet (4.57 m) landward of the shoreline must be built with 10 feet (3.05 m) of freeboard above the BFE using pile-constructed foundation [74]. Through policy recommendations, the City proposed code modifications, such as increasing the minimum elevation of living areas in residential buildings and the first floor of commercial, institutional, and industrial buildings and structures, to “the higher of either 7 feet (2.13 m) NGVD or 30 inches (0.76 m) [currently 18 inches (0.46 m)] above the highest point of any abutting street” [75]. Regarding an SLR-DFE, the City of Satellite Beach’s Sustainability Action Plan V2 [76] reports that “the City will use New York City’s (or equivalent) Climate Resiliency Design Guidelines [27] to establish a new required Design Floor [Flood] Elevation (DFE) for all new buildings in Satellite Beach. The new DFE will take into account future SLR scenarios extending out to 2070 and will add a freeboard (usually between 6 (0.15 m) and 24 inches (0.61 m))” [76].

3.1.6. Rhode Island (State)

Rhode Island provides a helpful example of modeling, along with online maps that inform an SLR-DFE at the parcel level (see Table 7). The developers of the mobile app, the RI Coastal Resources Management Council (RI CRMC), are a state agency established in 1971 to preserve, protect, develop, and, where possible, restore the state’s coastal resources through comprehensive planning and management [80] and the maps were originally developed through the Shoreline Change Special Area Management Plan (SAMP) team [81]. The CRMC is responsible for formulating policies, adopting regulations, and coordinating with local, state, and federal entities on coastal resource issues and is comprised of “representatives of the public and state and local government, and a staff of professional engineers, biologists, environmental scientists, and marine resources specialists” [80].
Their website provides online maps, including the STORMTOOLS Design Elevation (SDE), that represent “once in 100-year flooding and associated wave environment”, and SLR of varying depths [82]. Currently, STORMTOOLS shows coastal flooding but does not show freshwater flooding from rainfall or rivers or flooding entering streets through stormwater drains [83]. Freeboard is required above the BFE by the Special Area Management Plan, but it is unclear if freeboard is intended to be added to the SDE shown on the online STORMTOOLS maps.
The STORMTOOLS maps “provide the foundation for CRMC’s decision-making for coastal permit applications” [84]. “All new or expanding residential, commercial, industrial and/or other construction projects require RI Coastal Resources Management Council (CRMC) permitting if the project is within jurisdiction” [85], which is generally two hundred feet (60.96 m) inland from any coastal feature (e.g., coastal beaches, barriers, dunes, coastal wetlands, rocky shorelines, etc.) [86]. When a RI coastal property owner seeks a permit from RI CRMC, the applicant must complete a Coastal Hazard Application Worksheet and refer to their Viewer, which notifies the “applicant of potential coastal hazards that should be taken into consideration when planning shoreline development” [83]. The RI SAMP states that “the applicant will identify, document, and assess the feasibility of design techniques…to avoid or minimize risk of losses” [84].
This initiative is not included in the visual comparison graph in this paper because it uses multiple SLR scenarios.
Table 7. Rhode Island (State) DFE Approach 1.
Table 7. Rhode Island (State) DFE Approach 1.
Factor/CriteriaApproach
Author/EntityRI CRMC, Shoreline Change Special Area Management Plan, and STORMTOOLS.
Starting Elevation MeasurementOnce in 100-year (1% chance) return period storm scenario referenced to NAVD 88.
SLR Scenario and TimeframeChoose an appropriate design life and identify the associated projected sea level. The Coastal Hazard Application recommends a minimum 30 year “design life” be considered.
CRMC policy, RICRMP Section 145, relies on the “high” sea level change curve [84] included in the most recent NOAA sea level rise data [2].
  • 2030–1.67′ (0.51 m)
  • 2050–3.25′ (0.99 m)
  • 2080–6.69′ (2.04 m)
  • 2100–9.6′ (2.93 m)
SLR AdjustmentMaps illustrating SLR depths of 2′ (0.61 m), 3′ (0.91 m), 5′ (1.52 m), 7′ (2.13 m), 10′ (3.05 m) (are available in STORMTOOLS. 2
Maps illustrating a 100-year return period (1% annual chance) COASTAL STORM with or without 2 feet (0.61 m) of SLR are available in STORMTOOLS.
SLR scenarios are relative to 2010 and suggested design elevations are referenced to NAVD 88.
FreeboardRecommended: 1 foot (0.30 m) of freeboard (elevation) above BFE is required but up to 5 feet (1.52 m) of additional freeboard may be provided voluntarily. It is unclear if freeboard should be added to the SDE (described below).
Standards for Shallow Flooding Zones (A-Zones) in SFHZs:
  • Residential: 3′–0″ (0.91 m)
  • Non-residential: 3′–0″ (0.91 m)

Critical facilities: 2′–0″ (0.61 m) (minimum) lowest floor either elevated or dry floodproofed to or above the 500-year flood plus 2 feet (0.61 m) of freeboard
Design Flood ElevationsSLR-DFE = 100-year return period storm scenario + SLR based on design life + Freeboard
STORMTOOLS uses the term STORMTOOLS Design Elevation (SDE) to represent the “once in hundred year flooding and associated wave environment”, and SLR of varying depths (and does not mention freeboard).
ApplicationAll projects (new or expanding residential, commercial, industrial) within the CRMC jurisdiction require a CRMC permit.
Requirement or RecommendationFreeboard for substantial improvements for critical facilities is required.
Permit is required by the Coastal Resources Management Council (CRMC)’s jurisdiction (extending from the territorial sea limit to two hundred feet (60.96 m) inland from any coastal feature). Permit requires completion of Coastal Hazard Application Worksheet and Viewer and design evaluation.
SAMP includes additional adaptation recommendations from FM Global, an insurance company.
Note(s): 1 Information from the RI Coastal Resources Management Council (CRMC) SAMP [7,84,85]; 2 RI CRMC STORMTOOLS [81].

3.1.7. Federal Flood Risk Management Standard (National)

Spurred in 2015, the Federal Flood Risk Management Standard (FFRMS) is intended to be a “flexible framework to increase resilience against flooding and help preserve the natural values of floodplains and wetlands” [87]. However, ongoing scrutiny and criticism across multiple presidential administrations has led to the repeated adoption and revocation of the standard between 2017 and 2025. The FEMA FFRMS policy applies to all actions, including projects and/or portions of projects, where FEMA funds are used for new construction, substantial improvement, or to address substantial damage [88]. Title 44 § 9.6 of the Code of Regulations (CFR) outlines the required 8-step decision-making process to be followed by the Agency in applying the Orders to its actions [89] and priority of using of nature-based solutions [88].
Described in Table 8, the Standard “authorizes three approaches to establish the FFRMS flood elevation (‘how high’) and floodplain (‘how wide’)”, including the following: (1) The Climate Informed Science Approach (CISA); (2) Freeboard Value Approach (FVA); and (3) the 0.2% annual chance flood. The CISA is defined as “the elevation and flood hazard area that result from using the best-available, actionable hydrologic and hydraulic data and methods that integrate current and future changes in flooding, including climate change and other physical processes (e.g., land use change)” [28]. If the data is available, the CISA is the “preferred approach because it is the only approach that would ensure projects are designed to meet current and future flood risks unique to the location and thus would ensure the best overall resilience, cost effectiveness, and equity” [87]. When the CISA is not available, the FVA is used, which specifies adding 2 feet (0.61 m) to a BFE for non-critical actions and 3 feet (0.91 m) or the 0.2% annual chance flood for critical actions, whichever is higher. Critical actions are defined as “an action for which even a slight amount of flooding is too great”, and include (a) those that use or store highly volatile, flammable, explosive, toxic or water reactive materials, (b) hospitals and nursing homes, (c) emergency operation centers or data storage centers, or (d) generating plants [90].

3.2. Visual Comparison of SLR-Adjusted DFE

Figure 2 visually represents the amount of SLR adjustment and freeboard that make up the studied SLR-DFEs (or DFEs), and is required, except as noted for Satellite Beach. Note that the starting points for measuring the SLR-DFEs are varied and described in the legend.

4. Discussion

4.1. Observations and Challenges in the Development of SLR-Adjusted DFEs

The authors’ review of U.S. initiatives for establishing SLR-DFEs reveal a wide variation in approaches. The following sections describe key observations and challenges for each factor that makes up an SLR-DFE. The authors found that the standards that separated SLR adjustments from freeboard were most transparent and supported comparability across different initiatives.

4.1.1. Author/Entity

Authorship of the studied initiatives vary in scale, including federal, state, regional, county, city (or municipal), and district levels. In some cases, multiple initiatives might apply to one parcel, e.g., Florida’s state and regional initiatives.

4.1.2. Starting Point for Measuring SLR-DFEs

Most methods to establish an SLR-DFE start by adding additional height to the FEMA BFE. When the FEMA BFE is not the starting point for measuring the SLR-DFE, other methods refer to the adjacent street [71], Kauaʻi’s SLRFE [51] or Rhode Island’s SDE [81]. When multiple starting points for measurements are referenced in the same guidance, that which results in the highest elevation is usually selected.

4.1.3. SLR Scenario and Timeframe

For SLR scenarios, the State of Florida, Rhode Island, City of Miami Beach, and Kaua’i County use data from the interagency reports IPCC 2014 [91]; NOAA 2017 [65] or 2022 [2]. New York City uses data from the NYC Panel on Climate Change (NPCC) [43]. Boston uses the U.S. National Climate Assessment [46] and Satellite Beach draws from the U.S. Army Corps of Engineers’ [92] data. The initiatives apply the following SLR scenarios: intermediate–low (Florida State; Miami Beach); intermediate or “middle range” (Florida; New York City; Kauaʻi); intermediate–high (Miami Beach); and high scenario (Boston; Miami Beach; Satellite Beach; Rhode Island).
Some initiatives provide SLR amounts for a specific year, such as 2070 [44], while others provide a table where users can select SLR amounts based on multiple ranges for the building’s end of useful life up to 2100+ [27].
NYC’s SLR-DFE approach, defined in Table 5 of the Climate Resiliency Design Guideline [27], offers a helpful framework to which cities such as Miami Beach and Satellite Beach have referred. A key challenge to standardizing this method is selecting the appropriate SLR amounts for a given timeframe, which results from selecting different scenarios and is influenced by ongoing updates to climate data and modeling approaches.

4.1.4. SLR Adjustment

On the federal/national level, approaches from ASCE [36] and FFRMS [28,87] (except for the CISA approach), do not explicitly quantify an SLR adjustment. All other initiatives discuss SLR, but only NYC [27], Boston [44], and Kauaʻi [51] require an SLR adjustment in an SLR-DFE. The State of Florida [58], including the cities of Miami Beach [71] and Satellite Beach [73,74,79], consider SLR, but freeboard is their only mechanism that provides flood protection. Similarly, Rhode Island considers SLR as part of the permitting process but does not require it in an SLR-DFE [81].
To compare SLR adjustments across all initiatives, the authors selected a common year (2070), based on the scenario used from each. This resulted in the SLR amounts of ~25 inches (2.08 feet/0.63 m)) (50th percentile), 40 inches (3.33 feet/(1.01 m)) (high), 2 feet (0.61 m) (intermediate), 2.9 feet (0.88 m) (intermediate–high), 2.85 feet (0.87 m) (high), and 3.17 feet (0.97 m) (high).
Clearly describing the amount of SLR and the scenario it relates to, and whether the SLR adjustments are itemized (i.e., +16” (0.41 m) SLR) or included within a higher flood elevation than the FEMA BFE (e.g., Rhode Island’s SDE [81], Kauaʻi’s SLRFE [51]), help make the process understandable and replicable by others.

4.1.5. Freeboard

Freeboard is required by all the compared initiatives and is typically added to the FEMA BFE or a BFE adjusted for SLR. Each initiative requires either one (0.30 m), two (0.61 m), or three feet (0.91 m) of freeboard, while Miami Beach [71] and Rhode Island [81] allow additional height up to five feet. One initiative, the City of Satellite Beach, requires a conditional, minimum of ten feet (3.05 m) of freeboard in an area requiring a variance for new or replacement structures (see Table 6).

4.1.6. SLR-Adjusted Design Flood Elevations

The DFEs or SLR-DFEs (if SLR was accounted for) ranged from 1 to 10 feet (0.30 to 3.05 m) above the starting elevation, typically the FEMA BFE. The wide range reflects the differing starting points for measuring the SLR-DFE, such as above dune vegetation or adjacent street.
Methods for incorporating SLR in the SLR-DFE include (1) adding the FEMA BFE, an SLR adjustment, and freeboard, (e.g., NYC [27] and Boston [44]); (2) mapping SLR models and adding freeboard (e.g., Kauaʻi’s SLRFE [51]); or (3) mapping storms and SLR and adding freeboard (e.g., Rhode Island’s SDE [81].
A variety of terms are used in the initiatives studied. Miami Beach uses the term “finished floor elevation (FFE)”. RI uses “STORMTOOL design elevations (SDE)” and Satellite Beach uses “design floor [flood] elevation (DFE)” to describe elevations with SLR considered. In contrast, ACSE and FFRMS use the term “design flood elevation (DFE)” and only include the FEMA BFE and freeboard. Standardizing the term SLR-DFE, or similar, and its components, would improve clarity and facilitate comparison across initiatives.

4.1.7. Application

All initiatives applied to new construction or substantial improvement of buildings or structures. Each initiative applied to a geographic area, including jurisdiction (e.g., nation, state, city), flood zone (X, A, and V) or floodplain (100-year or 500-year). The initiatives applied to federally-funded buildings (e.g., FFRMS [28,87], state funded buildings (e.g., Florida [53], city capital projects (e.g., NYC [27], or all buildings (e.g., Boston [44]; Kauaʻi [51]; Miami Beach [71]; Satellite Beach [73,74,79]; and Rhode Island [81]).

4.1.8. Requirement or Recommendation

All the initiatives studied require a minimum freeboard, while an SLR adjustment is either required, recommended, or considered/mentioned, as described in the Freeboard and SLR Adjustment Sections above.
Some initiatives are required, such as ASCE Standard 24-14: Flood Resistant Design and Construction [36]; NYC Climate Resiliency Design Guidelines [27]; Boston Coastal Flood Resilience Design Guidelines [44]; Kauaʻi Sea Level Rise District (S-SLR) [51]; Florida sea-level impact projection (SLIP) studies [53]; Miami Beach Freeboard Ordinance (2016-4009) [71]; Satellite Beach Code of Ordinance § 30-555, 30-738-739 [73,74,79]; RI Special Area Management Plan (SAMP) [84]; and FEMA FFRMS (National Climate Task Force 2023). They are required through land use ordinances, building codes, legislation, or executive directives. Adherence is demonstrated by applications for zoning or use permits (e.g., Kauaʻi [49], applications for building permits (e.g., Miami Beach Land Development Regulation (Resiliency Code) [66], a worksheet during the permitting process (e.g., RI’s Coastal Hazard Analysis (CHA) Worksheet and Viewer [83]), or a two phase “Resilience Review” during the permitting process (e.g., Boston’s Coastal Flood Resilience Review [48]. FFRMS requires a public notice, the National Environmental Policy Act of 1969 (NEPA) review, a notice of findings, and additional information in new authorization or appropriation requests [93]. Florida requires the completion of a SLIP study, which must be submitted to the Department of Environmental Protection prior to construction [53].
Other initiatives are recommended, perhaps to socialize the concepts and build support prior to requiring them, such as FEMA’s Coastal Construction Manual and Designing for Flood Levels Above the Minimum Required Elevation After Hurricane Ian [15], 2019 Unified Sea Level Rise Projection Southeast Florida [63], Miami Beach Sea Level Rise Adaptation Plan [70], and City of Satellite Beach’s Sustainability Action Plan V2 [76].

4.2. Potential Application, Next Steps, and Future Research Needs

Locations seeking to establish an SLR-DFE can learn from the factors and methods used by the various initiatives in this study. The most informative examples defined the building’s lifetime and quantified the SLR adjustment separately from freeboard when creating an SLR-DFE. Locations can also learn from how other initiatives confirm a building project’s adherence to an SLR-DFE.
Municipalities seeking to create an SLR-DFE might learn from the information exchanged between planners and scientists, who were located near the communities studied, in particular, the SLR scenario, time ranges, and geographic extents of future flooding that informed the SLR-DFE guidance in a location.
Municipalities seeking to implement an SLR-DFE may consider an incremental approach by phasing by building type (e.g., city-owned buildings) or initiating voluntary adoption before requiring full compliance. For example, the NYC Guidelines [27] will first apply to selected city-owned pilot projects before being applied to all city-owned projects. Similarly, in 2019, Boston released and adopted its Coastal Flood Resilience Design Guidelines, while they proposed recommendations for a Flood Resilience Zoning Overlay District [47]. Then, in 2021, the city adopted the Coastal Flood Resilience Overlay District (CFROD) into its Zoning Code, requiring compliance with the SLR-DFE [47]. Implementing SLR-DFEs through pilot projects prior to widespread adoption can build support and inform future projects.
Municipalities planning to create similar online interactive flood maps might also consider integrating instructions side-by-side with the map viewer or providing video instructions. For example, the authors found the step-by-step instructions to determine an SLR-DFE were especially user-friendly in the online tools, e.g., Rhode-Island’s STORMTOOLS [81] and the FEMA Federal Flood Standard Support Tool [93].
The team identified several potential future research needs.
  • As the initiatives studied are implemented, future research on new and renovated buildings is needed to evaluate the SLR-DFE’s ease of application, adherence rate, first cost, effectiveness during a flood, potential cost savings, etc.
  • Quantify an SLR-DFE that includes SLR in combination with wave velocity in the FEMA FIRM Zone V or VE areas.
  • Understand if or when an SLR-DFE should consider the water level described by the 1% annual exceedance probability level, which combines astronomical tide, storm surge, and limited wave setup, but excludes wave runup [94]. This is different from the FEMA FIRMs BFE 1% annual chance flood.
  • Given increased frequency and intensity of heavy precipitation [95], the SLR-DFEs could be compared and refined based on observed flood depths from large rainfall events that can be estimated through AI-processing of photos in flooded areas [96].

5. Conclusions

Establishing Local Building Elevation Levels for an SLR Affected Future

This study compares current developments in SLR-DFEs that go beyond FEMA FIRMs that only consider historical flood data. The various initiatives use guidelines, policies, and online maps and tools. The tables, discussion, and comparison graph in this paper are resources for policymakers and design teams as they develop their own SLR-DFEs. The analysis underscores the potential for more consistent methods to establish an SLR-DFE, particularly the explicit quantification of the SLR adjustment.
The initiatives’ authors range in scale, including federal, state, regional, and municipal. Most initiatives started measuring the SLR-DFE from the FEMA FIRM BFE. The initiatives’ timeframes and SLR scenarios used to establish an SLR-DFE vary, and are sometimes determined by the buildings’ end of useful life. The SLR adjustments are based on scientific data for the location they serve. Freeboard is typically 1–3 feet (0.30–0.91 m), and additional building height is sometimes allowed. The SLR-DFEs typically ranged from about 2–5 feet (0.61–1.52 m) above the FEMA FIRM BFE from about 2020–2100. The initiatives are typically applied to a mapped flood hazard zone. The initiatives applied to a range of building types: federal; state; city; or all buildings. Some initiatives are recommended but not enforced, while others are required and verified (e.g., during building permitting). The authors’ main suggestion to building designers is to plan for SLR amounts within the building’s lifetime.
As SLR-DFEs are implemented in more coastal communities, future research could examine reduced damage from flooding and life cycle costs to inform robust future flood resilience initiatives.

Supplementary Materials

A spreadsheet which combines all tables: https://tinyurl.com/yc5c968m (accessed 1 July 2025).

Author Contributions

Conceptualization, W.M.; methodology, W.M., E.T.; validation, W.M., J.I.B.; investigation, E.T., J.I.B. and W.M.; resources, W.M., C.H.F.; writing—original draft preparation, E.T., J.I.B., and W.M.; writing—review and editing, W.M., J.I.B. and E.T.; visualization—preparation, E.T. and J.I.B.; visualization—review and editing, W.M., J.I.B.; project administration, W.M.; funding acquisition, W.M., C.H.F. All authors have read and agreed to the published version of the manuscript.

Funding

This paper is funded by the Office of Naval Research and a grant/cooperative agreement from the National Oceanic and Atmospheric Administration, Project R/IR-51 and A/AS-1, which is sponsored by the University of Hawaiʻi Sea Grant College Program, SOEST, under Institutional Grant No. NA18OAR4170076 and NA24OARX417C0024-T1-01 from NOAA Office of Sea Grant, Department of Commerce. The views expressed herein are those of the author(s) and do not necessarily reflect the views of NOAA or any of its subagencies. UNIHI-SEAGRANT-4951.

Acknowledgments

The authors appreciate the collaboration and in-kind support from the University of Hawaiʻi School of Architecture’s Environmental Research and Design Laboratory, Sea Grant College Program’s Center for Smart Building and Community Design, and the School of Ocean and Earth Science and Technology’s Coastal Research Collaborative.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Abbreviations

The following abbreviations are used in this manuscript:
SLRsea level rise
BFEbase flood elevation
DFEdesign flood elevation
SLR-BFEsea level rise-adjusted base flood elevation
SLR-DFEsea level rise-adjusted design flood elevation
FEMAFederal Emergency Management Agency

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Figure 1. A simplified illustration of a building comparing hypothetical height and factors included in a DFE (on the left) and SLR-DFE (on the right). Credit: Briones, J.; Teeples, E.; Meguro, W.
Figure 1. A simplified illustration of a building comparing hypothetical height and factors included in a DFE (on the left) and SLR-DFE (on the right). Credit: Briones, J.; Teeples, E.; Meguro, W.
Water 17 02376 g001
Figure 2. Visual Comparison of SLR-Adjusted DFE Methods, including ASCE-24-14 Flood Resistant Design and Construction [36]; NYC Resilience Design Guidelines [27]; Boston Coastal Flood Resilience Design Guidelines [43]; Kauaʻi Constraint District: Sea Level Rise District (S-SLR) [51]; City of Miami Beach Ordinance No. 2016-4009 (2016) [71]; Satellite Beach. Code of Ordinances. § 30-739 [74]; and Federal Flood Risk Management Standard: Freeboard Value Approach (FVA) [28,87]. Credit: Briones, J.; Teeples, E.; Meguro, W.
Figure 2. Visual Comparison of SLR-Adjusted DFE Methods, including ASCE-24-14 Flood Resistant Design and Construction [36]; NYC Resilience Design Guidelines [27]; Boston Coastal Flood Resilience Design Guidelines [43]; Kauaʻi Constraint District: Sea Level Rise District (S-SLR) [51]; City of Miami Beach Ordinance No. 2016-4009 (2016) [71]; Satellite Beach. Code of Ordinances. § 30-739 [74]; and Federal Flood Risk Management Standard: Freeboard Value Approach (FVA) [28,87]. Credit: Briones, J.; Teeples, E.; Meguro, W.
Water 17 02376 g002
Table 1. ASCE Standard 24-14 (National) DFE Approach 1.
Table 1. ASCE Standard 24-14 (National) DFE Approach 1.
Factor/CriteriaApproach
Author/EntityAmerican Society of Civil Engineers (ASCE)
Starting Elevation MeasurementMeasured from FEMA BFE.
SLR Scenario and TimeframeDoes not incorporate SLR projections.
SLR AdjustmentN/A—freeboard is the primary elevation method used.
FreeboardClass 1 = 0′
Class 2 = 1′ (0.30 m)
Class 3 = 2′ (0.61 m)
Class 4 = 2′ (0.61 m)
Design Flood Elevations
  • Class 1 = DFE *
  • Class 2 = BFE + 1′ (0.30 m) or DFE *, whichever is highest
  • Class 3 = BFE + 2′ (0.61 m) or DFE *, whichever is higher
  • Class 4 = BFE + 2′ (0.61 m) or DFE *, or 500-year flood elevation, whichever is higher

* For ASCE Standard 24-14, the DFEs are the flood elevations shown on the map adopted by a community (if not using FEMA FIRMS).
For buildings within Coastal High Hazard Areas, Coastal A Zones, and High Risk Flood Hazard Areas: the minimum elevation (listed above) is measured to the bottom of the lowest supporting horizontal structural member of the lowest floor.
For buildings within all other Flood Hazard Zones: the minimum elevation is measured to the top of the lowest floor.
ApplicationASCE Standard 24-14 applies to new construction or substantial improvement of buildings and structures in flood hazard areas.
Requirement or RecommendationRequired for all structures subject to building code requirements in flood hazard areas.
Note(s): 1 Information from the ASCE Standard 24-14, Flood Resistant Design and Construction [36].
Table 3. City of Boston (Municipal) DFE Approach 1.
Table 3. City of Boston (Municipal) DFE Approach 1.
Factor/CriteriaApproach
Author/EntityBoston Planning and Development Agency (BPDA)
Starting Elevation MeasurementMeasured from FEMA BFE, which uses the Boston City Base (BCB) as their city-wide datum. NAVD88 can be converted to BCB by using a conversion factor of NAVD88 + 6.46 feet (1.97 m).
SLR Scenario and TimeframeBoston Harbor Flood Risk Model (BH-FRM) is a localized scenario that utilizes data from the U.S National Climate Assessment from [46]. The projection is set for the year 2070 for the “High” scenario.
SLR Adjustment40″ (1.02 m) SLR adjustment (3.2′ (0.98 m) SLR + 2.5″ (0.06 m) land subsidence)
Freeboard1′–0″ (0.30 m): all buildings—existing/retrofit
2′–0″ (0.61 m): planned/new construction or residential use, or uses, which are conditional within the overlay
Design Flood ElevationsSLR-DFE = FEMA BFE + SLR Adjustment + Land Subsidence + Freeboard
ApplicationGuides private development. Applies to all structures within the overlay zone (BH-FRM), which includes areas “anticipated to be flooded with a 1% chance storm event in 2070 with 40-inches (1.02 m) of sea level rise.” (includes 2.5″ (0.06 m) of land subsidence)
Requirement or RecommendationRequired within the Coastal Flood Resilience Overlay District (CFROD); Section 25A-6
Note(s): 1 Information from the Boston Coastal Flood Resilience Design Guidelines [43,45,47,48].
Table 4. Kauaʻi, Hawaiʻi (County and District) DFE Approach 1.
Table 4. Kauaʻi, Hawaiʻi (County and District) DFE Approach 1.
Factor/CriteriaApproach
Author/EntityCounty of Kauaʻi
Starting Elevation MeasurementUses a sea level rise flood elevation (SLRFE) or FEMA FIRM BFE (if higher). Sea level rise flood elevation (SLRFE) is the individual depth above existing grade per grid unit provided by the County of Kauai Sea Level Rise Constraint District Viewer for both the high wave run up hazard and the passive flooding hazard when either of those are associated with 3.2 feet (0.98 m) of SLR occurring within this century.
SLR Scenario and TimeframeUses Hawaiʻi’s sea level rise exposure area (SLR-XA), which includes passive flooding and annual high wave flooding, and coastal erosion is based on the high GHG emissions scenario (RCP8.5) used to model exposure to sea level rise 3.2 feet (0.98 m) by 2100. 2
SLR AdjustmentFlood depth indicated by SLRFE.
Freeboard1′–0″(0.30 m): nonresidential
2’–0″(0.61 m): residential
Design Flood ElevationsDFE = SLRFE or BFE + Freeboard (within the ST-CE and S-SLR)
ApplicationResidential and non-residential new construction and major renovation within the S-SLR constraint district.
Requirement or RecommendationRequired in the S-SLR, which is monitored through the use permitting process.
Note(s): 1 Information from the County of Kauaʻi Planning Department [51]; 2 Hawaiʻi Sea Level Rise Vulnerability and Adaptation Report [52].
Table 5. Miami Beach, Florida (Municipal) DFE Approach 1.
Table 5. Miami Beach, Florida (Municipal) DFE Approach 1.
Factor/CriteriaApproach
Author/EntityCity of Miami Beach
Starting Elevation MeasurementUses the highest point of adjacent road or above the crown of the nearest street (Flood Zone X) or FEMA BFE (Flood Zone A).
SLR Scenario and Timeframe“The years 2040 and 2070 were chosen because they represent a near- and long-term planning horizon, respectively. Two of the sea level rise scenarios (NOAA 2017 Intermediate–Low and NOAA 2017 Intermediate–High) were selected to comply with the Resilient Florida program. The City included a third scenario (NOAA 2017 High), which represents a more rapid rise in future sea level, as a more extreme scenario that can potentially be used for developing adaptation strategies for critical infrastructure (e.g., emergency facilities)”.
SLR AdjustmentSLR Adjustment is not required, but the SLR Adaptation Plan 2 discusses SLR in the FFE.
NOAA 2017 1:
Intermediate–Low
  • 2040–0.3′ (0.09 m)
  • 2070–0.9′ (0.27 m)

Intermediate–High
  • 2040–1.0′ (0.30 m)
  • 2070–2.9′ (0.88 m)

High (critical)
  • 2040–1.3′ (0.40 m)
  • 2070–4.1′ (1.25 m)
FreeboardRef. [71], §54-35; 54-48; 54-51:
1′ (0.30 m) (min.)–5′ (1.52 m) (max.)
Specifically:
Flood Zone X: 1 foot (0.30 m) (min.) above the highest adjacent grade or above the crown of the nearest street; whichever is higher.
Except seaward of the Coastal Construction Control Line and in Coastal A Zones, All Flood Zone A:
  • Non-Residential/Residential: 1 foot (0.30 m) (min.) above the BFE “no lower than 9.0 feet (2.74 m) NGVD (7.44 ft (2.27 m) NAVD), the crown of road or sidewalk plus one (0.30 m) foot, or the base flood elevation plus minimum freeboard, whichever is higher.”
  • Critical: 2 ft (0.61 m) (min.) above the BFE

Flood Zone V and Coastal A Zone: meets all the above and in addition elevated on pilings or columns plus freeboard “no lower than 8.0 feet (2.44 m) NGVD (6.44 feet (1.96 m) NAVD), the crown of road or sidewalk plus one (0.30 m) foot, or the base flood elevation plus minimum freeboard whichever is higher”.
Design Flood ElevationsDFE = BFE or highest adjacent grade or above the crown of the nearest street + (1′ (0.30 m)–5′ (1.52 m)) freeboard
ApplicationFreeboard: all new construction and substantial improvements to existing construction as described in the Flood Zones above
Requirement or RecommendationFreeboard is required as described in the Flood Zones above 1. The SLR Adaptation Plan 2 discusses SLR in the FFE.
Note(s): 1 Information from the City of Miami Beach. Code of Ordinances: Chapter 54-Floods [71]; NOAA 2017 [65]. 2 City of Miami Beach Sea Level Rise Adaptation Plan (draft) [70].
Table 6. Satellite Beach, Florida (Municipal) DFE Approach 1.
Table 6. Satellite Beach, Florida (Municipal) DFE Approach 1.
Factor/CriteriaApproach
Author/EntityCity of Satellite Beach
Starting Elevation MeasurementFEMA BFE or highest point of abutting street
SLR Scenario and TimeframeIn their 2019 Sea-Level Rise Technical Planning Assessment [77], the city acknowledges data from the U.S. Army Corps of Engineers [78] “High” Scenario, which was derived from the U.S. Army Corps of Engineers Sea-Level Change Calculator (accessed 6 July 2018;). Projection through the year 2070.
SLR AdjustmentSLR Adjustment is not required, but the Sustainability Action Plan V2 2 discusses SLR incorporated into future DFEs.
USACE “High” Scenario (2070): 2.85 feet (0.87 m) above 1992 mean sea level (MSL).
FreeboardCommercial, Institutional and Industrial: minimum 18 inches (0.46 m) (current requirement)/30 inches (0.76 m) (recommended code modification) above the highest point of any abutting street.
Residential: “above the dune vegetation on stilts/pilings to a minimum of three feet (0.91 m) above the BFE” if located east of Highway A1A. An owner may elevate the structure more than three feet (0.91 m) above the BFE as desired and if approved by the building official and in accordance with FEMA and NFIP standards.
Variance: Property less than 15 feet (4.57 m) landward of the construction control line (CCL): 10 feet (3.05 m) above the BFE.
Design Flood Elevations=Street + 18–30″ (0.46–0.76 m)
=BFE + 3′ (0.91 m)
=BFE + 10′ (3.05 m)
Application“construction, reconstruction, modification, repair or replacement of principal or accessory structures or portions thereof for all properties located east of Highway A1A.”
Requirement or RecommendationFreeboard: required. Note recommended code modification (above).
Note(s): 1 Information from the Satellite Beach, Florida-Code of Ordinance § 30-555 and 30-738-739 [73,74,79] 2019 Sea-Level Rise Technical Planning Assessment [77]. 2 City of Satellite Beach’s Sustainability Action Plan V2 [76].
Table 8. Federal Flood Risk Management Standard (National) Approach 1.
Table 8. Federal Flood Risk Management Standard (National) Approach 1.
Factor/CriteriaApproach
Author/EntityFFRMS Science Subgroup of the Flood Resilience Interagency Working Group of the National Climate Task Force.
Starting Elevation MeasurementFEMA BFE is used for the Freeboard Value Approach (FVA) and 0.2% Annual Chance Flood Approach.
SLR Scenario and TimeframeUses best-available science when using the Climate Informed Science Approach (CISA) (if climate science data is available).
SLR AdjustmentDetermined by climate science data (if CISA is available).
FreeboardFor FVA (only):
  • Non-Critical action: 2′–0″ (0.61 m)
  • Critical actions: 3′–0″ (0.91 m)
Design Flood ElevationsIf CISA is not available, the FVA is as follows:
  • Non-Critical action: DFE = BFE + 2 ft (0.61 m)
  • Critical actions: DFE = BFE + 3 ft (0.91 m) or 2% annual chance flood (whichever is higher)
ApplicationFEMA-funded projects involving new construction, substantial improvement, or repairs to address substantial damage.
Requirement or RecommendationRequired for FEMA-funded projects.
Note(s): 1 Information from the FFRMS CISA State of the Science Report [28,87].
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Meguro, W.; Briones, J.I.; Teeples, E.; Fletcher, C.H. Establishing a Sea Level Rise-Adjusted Design Flood Elevation for Buildings: A Comparative Study of Methods. Water 2025, 17, 2376. https://doi.org/10.3390/w17162376

AMA Style

Meguro W, Briones JI, Teeples E, Fletcher CH. Establishing a Sea Level Rise-Adjusted Design Flood Elevation for Buildings: A Comparative Study of Methods. Water. 2025; 17(16):2376. https://doi.org/10.3390/w17162376

Chicago/Turabian Style

Meguro, Wendy, Josephine I. Briones, Eric Teeples, and Charles H. Fletcher. 2025. "Establishing a Sea Level Rise-Adjusted Design Flood Elevation for Buildings: A Comparative Study of Methods" Water 17, no. 16: 2376. https://doi.org/10.3390/w17162376

APA Style

Meguro, W., Briones, J. I., Teeples, E., & Fletcher, C. H. (2025). Establishing a Sea Level Rise-Adjusted Design Flood Elevation for Buildings: A Comparative Study of Methods. Water, 17(16), 2376. https://doi.org/10.3390/w17162376

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