ASCE 24-24 Delivers Major Update to Flood Resistant Design Standards
A new national standard could significantly change how communities mitigate flooding. The American Society of Civil Engineers (ASCE) has released Flood Resistant Design and Construction, ASCE/SEI 24-24, an update to its widely used standards for structures in flood hazard areas.
The 2024 edition provides minimum requirements for flood resistant design and construction of structures that are subject to building code requirements, floodplain management regulations, or other requirements that cite this standard. ASCE 24-24 contains significant changes from the previous version, ASCE 24-14, and aligns with the ASCE 7-22 Supplement 2 for design flood loads, which was released in May 2023.
“This may be the most significant upgrade in the nation’s flood loss reduction standards since the creation of the NFIP minimums in 1973, and it could not come at a better time as annual flood losses in the country now average more than $45 billion/year,” said Chad Berginnis, CFM, Executive Director of ASFPM.
Among numerous provisions contained in this standard, four primary updates stand out:
- Expanded flood hazard area. The flood hazard area is redefined to include the 500-year floodplain (where it is mapped as Shaded X Zone or Zone B or C on some older FIRMs) as well as the 100-year floodplain (SFHA).
- Elevation requirements are tied to the flood design class of the structure. The assignment of the flood design class is based on a building or structure’s risk to human life, health and welfare if affected by flooding. For most residential, commercial, and industrial structures, this is the 500-year mean recurrence interval (MRI) flood event. For more important facilities, it is either the 750-year (buildings and structures that pose a high risk to the public or significant disruption to community) or 1,000-year (buildings and structures that contain essential facilities and services necessary for emergency response and recovery) MRI flood event. Only certain accessory and agricultural structures would be allowed at the 100-year MRI flood elevation.
- Climate change considerations. Coastal floodplain calculations must now factor in future sea level change based on historic trends.
- Enhanced dry floodproofing requirements. The standard overhauls requirements for dry floodproofing, including the required use of ANSI/FM 2510- certified products and updates to inspection and maintenance needs, and flood emergency operation plans.
How Model Codes and Standards are Developed
ASCE 24-24 was developed by the Flood Resistant Design and Construction Standards Committee of the Structural Engineering Institute of ASCE. Model codes and standards are developed by experienced volunteer professionals working together through a multi-step, consensus-based process. Often, provisions start as case study reports or research papers before evolving into guidelines, then standards, and finally incorporation into model codes.
ASCE, as a premier American National Standards Institute (ANSI)-approved standards organization, develops and maintains many of the standards referenced or incorporated in the model building codes. Through a thoughtful and extensive process, ASCE assures that each standard represents a broad consensus of the related professional community. The standards developed by the U.S. voluntary consensus standards system empower our nation domestically and globally.
“The primary objectives of the ASCE 24-24 Committee were to align the requirements in ASCE 24 with ASCE 7-22 Supplement 2 and update the standard to incorporate insights gained since it was last updated 10 years ago,” said Manny Perotin, co-chair of ASFPM’s Nonstructural Floodproofing Committee and one of the volunteers who served as an associate member on the committee that helped develop the standard. “While there is nothing foolproof about wet or dry floodproofing, the updates to this standard help communities and design professionals construct buildings that are more flood resistant. I encourage federal, state, and local officials to consider incorporating these requirements along with other best practices like proper planning and zoning, continuing to advance their flood hazard data, and delivering training to help properly adopt and enforce these new requirements to help continue reducing flood property damage.”
“One factor we haven’t understood well is how much protection one or two feet of freeboard supplies,” said Dr. Carol Friedland, ASCE 24 committee member and director of the LaHouse Research and Education Center at the Louisiana State University (LSU) AgCenter. “Through the process of updating the ASCE 24 standard, we found that a fixed freeboard amount provides variable protection depending on the location. Moving to a return period or probability basis protects everyone to the same level, regardless of where they are in the country. This is a significant improvement over previous flood protection approaches.”
What’s Next?
The International Code Council (ICC) produces a series of model codes known as the I-Codes. The most recent editions — the 2024 I-Codes — are due for an update in 2027 and that process has already begun. ASCE 7 and ASCE 24 have long been the reference standards related to flooding in the I-Codes. As such, proposals are already being developed to have ASCE 24-24 be considered for 2027 I-Codes update.
But there’s no reason to wait for the building codes.
“Over 22,000 communities participate in the NFIP and as such have adopted floodplain management regulations,” said Berginnis. “Why not adopt the relevant sections of ASCE 24-24 directly into a community’s floodplain management standards?”
Steps to Facilitate Adoption
ASFPM is taking action to make it easier for communities to adopt ASCE 24-24 including:
- Raise awareness of the standard. ASFPM’s Non-Structural Floodproofing Committee is working on a webinar to introduce the standard to our members. Additionally, the association is developing a workshop for the ASFPM Annual Conference and will make additional training materials available.
- Facilitate easy access to and use of the standard. ASFPM is trying to reduce barriers accessing the standard and is working with ASCE to develop solutions. The LSU AgCenter has developed an easy-to-use, web-based calculator to determine the required elevations for different flood design classes based on the new ASCE 24-24 requirements.
- Update ASFPM’s model higher standards guide to include language to facilitate adoption of the ASCE 24-24 requirements into floodplain management standards.
- Engage with states. ASFPM is working with states to become more familiar with the standard and to potentially incorporate it into a state’s model ordinance as a suggested higher standard.
“The beauty of having a national consensus standard is that it didn’t come from the government and it can’t be taken away by the government,” said Berginnis. “It is what the practitioner community says is needed to reduce flood losses in the nation. Whether it is used to backstop states and communities that already have higher standards like a 2 foot freeboard or gives the impetus needed to adopt a higher standard, we cannot continue to do things like we have been doing, flood losses are increasing far too fast.”
To learn more about the standard or obtain a copy, visit the ASCE library.
