Mitigation Design Standards & Guidelines

Engineering Data Fact Sheet

While the project type determines the specific engineering data requirements, typical engineering data needed is included in this fact sheet and divided into a variety of project types.  The Fact sheet outlines Drainage projects, Elevation projects, Building elevations and Wind retrofit projects.  

Link to the Engineering Data Fact Sheet.

While the project type determines the specific engineering data requirements, typical engineering data needed is included in this fact sheet and divided into a variety of project types.  The Fact sheet outlines Drainage projects, Elevation projects, Building elevations and Wind retrofit projects.  

FLOOD DESIGN AND PLANNING CONSIDERATIONS


 

Flood Supplement for ASCE 7-22

The American Society of Civil Engineers (ASCE) has released a new supplement to the 2022 edition of its widely used standard titled ASCE/SEI 7: Minimum Design Loads and Associated Criteria for Buildings and Other Structures (ASCE 7-22). The release of the ASCE 7-22 supplement (2) on flood loads marks a milestone in advancing flood-resilient building design. It focuses on flood load provisions and introduces significant improvements to enhance the resilience of buildings against extreme flood events. This update surpasses the previous edition, which primarily focused on the 100-year flood hazard, by implementing minimum recurrence intervals of 500-, 750-, and 1000-years to improve structure reliability throughout its design life.

The new supplement adopts risk-based approaches and aligns with the prevailing trend of using higher minimum recurrence intervals to enhance building design resilience. The supplement ensures flood load calculation consistency with other hazards addressed in the standard, such as wind and seismic design, which also use higher recurrence intervals for load calculations.

Noteworthy technical updates within the supplement include revised minimum design requirements, which incorporate sea level change and adjustments to the calculations of hydrostatic and hydrodynamic loads (such as velocity and scour), wave loads, debris loads, flood load cases, load combinations and stability checks. These updates reflect a departure from previous versions of ASCE 7 and signify society’s commitment to integrating climate data into its standards.

In conclusion, the new ASCE 7-22 Supplement 2 on flood loads represents a significant advancement in flood-resilient building design. By embracing the 500-year flood hazard area and incorporating risk-based approaches, the supplement enhances the safety and reliability of structures, instilling confidence in residents and businesses facing weather-related challenges. The release of this supplement as a free download reflects ASCE’s commitment to disseminating vital engineering knowledge and promoting the highest standards in the industry.


 

Highlights of ASCE 24 Flood Resistant Design and Construction

May 6. 2021

The American Society of Civil Engineers (ASCE) 24-05 is a referenced standard in the International Building Code® and International Residential Code® (editions published 2012, 2009 and 2006). Building and structures within the scope of the IBC proposed to be constructed in a flood hazard area must design in accordance with ASCE 24. The IRC requires that dwellings in floodways to be designed in accordance with ASCE 24, and the 2012 and 2009 editions include an alternative that allows communities to require homes in Zones V to be designed in accordance with ASCE 24. Highlights of ASCE 24 that complement the NFIP minimum requirements include Building Performance; Flood-Damage Resistant Materials; Utilities and Service Equipment; and Siting Considerations.

Link to the Highlights https://www.fema.gov/sites/default/files/2020-07/asce24_highlights_dec2010.pdf


 

Guidance for Applying ASCE 24 Engineering Standards to HMA Flood Retrofitting and Reconstruction Projects

November 2013

This ASCE 24 HMA Guidance was prepared by the FEMA to assist local governments, designers, and property owners.  It identifies key design and construction requirements in the ASCE Structural Engineering Institute’s ASCE/SEI 24-05, Flood-Resistant Design, and Construction (ASCE 24) that apply to HMA flood mitigation grant projects.  

This document is in no way intended to be used in place of ASCE 24 but rather as a companion to the standard.  Designers, local officials, and others who want to apply the standard still need to refer to the standard for complete requirements.

The guidance does not advocate construction in the floodplain; rather, it is intended to reduce hazard risk for situations in which there is no practicable alternative.  The emphasis of this document is on mitigation if construction in the floodplain is not avoidable, although the best way to greatly reduce (if not eliminate) flood risk is to relocate a structure out of the floodplain.  The term “must” is used in the context of the ASCE 24 design standard to indicate compliance to applicable criteria within ASCE 24.


 

Minimum Design Standards for HMA Projects in Flood Hazard Areas

FEMA will use the American Society of Civil Engineers (ASCE) Flood Resistant Design and Construction or its equivalent as the minimum design criteria for all HMA funded structure elevation, dry floodproofing, and mitigation reconstruction projects in flood hazard areas. 

Flood Resistant Design and Construction, ASCE/SEI 24-14, provides minimum requirements for design and construction of structures located in flood hazard areas and subject to building code requirements. Identification of flood prone structures is based on flood hazard maps, studies, and other public information. This standard applies to new structures, including subsequent work, and to work classified as substantial improvement of existing structures that are not historic. Standard ASCE/SEI 24-14 introduces a new concept, Flood Design Class, that bases requirements for a structure on the risk associated with unacceptable performance.

The standard includes requirements for the following: basic siting and design and construction requirements for structures in flood hazard areas; minimum elevations for the lowest floor, flood damage-resistant materials, and floodproofing measures, each tied to a structure’s Flood Design Class; structures in high risk flood hazard areas subject to flooding associated with alluvial fans, flash floods, mudslides, erosion, high velocity flow, coastal wave action, or ice jams and debris; flood damage-resistant materials; dry floodproofing and wet floodproofing; attendant utilities and equipment, including electrical service, plumbing systems, mechanical/HVAC systems, and elevators; building access; and miscellaneous construction, including decks and porches, concrete slabs, garages and carports, accessory storage structures, chimneys and fireplaces, pools, and tanks. A detailed commentary containing explanatory and supplementary information to assist users of the standard is included for each chapter.

Standard ASCE/SEI 24-14 updates and replaces the previous Standard, ASCE/SEI 24-05. It provides essential guidance on design and construction to structural engineers, design professionals, code officials, floodplain managers, and building owners. The standard is adopted by reference in model building codes.


Engineering Principles and Practices for Retrofitting Flood-Prone Residential Structures 

January 1, 2012

The third edition of Engineering Principles and Practices is intended to further aid homeowners in selecting and successfully executing a flood retrofit on their home.  Engineering design and economic guidance on what constitutes feasible and cost-effective retrofitting measures for flood-prone residential and non-residential structures are presented.  Elevation, relocation, dry floodproofing, wet floodproofing, and the use of levees and floodwalls to mitigate flood hazards are discussed.  This edition was updated to be more user-friendly and concise, the overall length of the publication has been shortened.

 


Subdivision Design and Flood Hazard Areas 

The subdivision of land in or near floodplains involves the potential creation of tomorrow’s flood risks. In an era of increasing attention to climate change, those risks may be greater than they have been in the past.

APA has a long history of addressing these issues, dating back at least to its 1997 publication of Subdivision Design in Flood Hazard Areas (PAS Report No. 473, 1997).

Now, in partnership with the Association of State Floodplain Managers, and with funding from the Federal Emergency Management Agency, we are revisiting the topic to provide updated guidance on the subject for local planners, consultants, and others involved in the subdivision design and site plan review process. The need is clear for much more technical guidance related to all aspects of subdivisions, from planning to design, to standards, to infrastructure maintenance.

The new PAS Report will benefit from a larger effort at partnership between APA and ASFPM on a number of fronts. Both organizations have been leaders in the NOAA Digital Coast Partnership. APA and ASFPM are partnering also on a new project called the Planning Information Exchange, funded under the same agreement with FEMA, to provide educational webinars on hazard mitigation planning. And we are exploring other areas as well that we consider grounds for potential fruitful collaboration. Planners and floodplain managers have many common goals, and our two organizations even have some overlapping membership. Both bring valuable expertise to this project.

What We Will Produce

  1. A new PAS Report whose focus would be broadened from the strict subdivision approach used in PAS Report No. 473 to include other land-use regulatory considerations affecting design in flood hazard areas, specifically including PUD regulations and design review, but also innovations in coastal and floodplain zoning and regulation.
  2. Web-based enhancements to expand the outreach potential of the project. Examples of web-based resources would include an inventory of the best sample ordinances, checklists for regulatory consideration, an annotated bibliography, and a glossary. In the past, some of these might have been included in a printed PAS Report, but in recent years APA has adopted the practice of placing these resources online in order to make them more accessible while also producing a slimmer, more accessible printed report. A downloadable PDF version of the report will also be made available.
  3. Professional training opportunities based on the report’s findings, such as presentations at the national and state chapter conferences of both partner organizations managing the project. APA and ASFPM can also propose additional derivative products for FEMA consideration toward the end of the project, if desired. APA and FEMA have collaborated on such derivative products in connection with two other APA projects in the last five years.

Why This Project?

Obviously, much has changed since APA’s PAS Report 473, Subdivision Design in Flood Hazard Areas, was published in 1997. The CRS  was then still in its infancy, having only been developed in 1990. Sustainability and resiliency were just words found in the dictionary and not necessarily a focus of land development. No one had given much thought to adapting to our ever-changing climate. Project Impact was launched the same year, and the NFIP was approaching its 30th birthday in 1998.

Almost 20 years later, sustainability, resilience, climate change, and related topics are at the forefront of attention for planners, floodplain managers, and related professionals. However, subdivision practices have seen relatively little change, especially where they concern comprehensive floodplain management. The benefit provided by this project relates to this basic need.

APA, the nation’s lead organization in the planning profession, and ASFPM, the nation’s premier floodplain management organization, are partnering to address the needs of the urban planning and floodplain management professions by providing modern-day assistance on “sound” subdivision guidelines and related regulatory practices such as planned unit development (PUD) design, emerging tools such as the coastal resilience zone, and issue areas such as climate adaptation and No Adverse Impact to name a few of the areas of emphasis.

The idea behind this update, in part, is to focus on breaking the build-damage-rebuild cycle our nation now finds itself in, to reduce risk from flood damages, and to incorporate best planning practice guidance, as well as other aspects of floodplain management. It is quite obvious that a community cannot be sustainable or resilient without safe places to live, work, and play.

One need merely look at the damage to the housing stock and the loss of life from Hurricanes Sandy and Katrina or events such as the Colorado flood of 2013 or the Atlanta flood of 2009, to see the need for and the practical utility of the proposed update to PAS 473. It is about saving lives and protecting property at its foundation and about building a future for our residential communities that are free from, or at least have a reduced risk to, flooding.

 

Second-Story Conversion – Elevation Project Design Considerations for HMA Applicants

Elevation is a common mitigation method for structures that are at risk of flooding, and is an eligible mitigation project under the FEMA HMA Grant Programs.  Structure elevation activities generally involve physically raising an existing structure in accordance with the 2015 HMA Guidance, or latest edition, and the American Society of Civil Engineers (ASCE) standard Flood Resistant Design and Construction (ASCE 24-14), or latest edition. 

ASCE 24-14 includes elevation to the Base Flood Elevation [BFE] plus freeboard, or higher when required by FEMA, local ordinance, or building code.  Structure elevation may be achieved through a variety of methods, including elevating on continuous foundation walls; elevating on open foundations, such as piles, piers, posts, or columns; and elevating on fill.  There are situations, such as structures with a slab-on-grade foundation, where physically raising the building is not feasible or cost-effective.  FEMA conducted research to identify alternative flood mitigation methods to address these types of situations and published this information as recovery advisories.

The purpose of the  Second Story Conversion Elevation Fact Sheet is to identify project design considerations that should be taken into account when developing these types of HMA-funded elevation projects.


 

FEMA P-936, Floodproofing Non-Residential Buildings

The primary focus of the guidance document is on dry floodproofing technologies for non-residential buildings, but it also includes an overview of other techniques including wet floodproofing and the use of levees and floodwalls. The publication provides information about regulatory requirements, design considerations, and descriptions of floodproofing methods and equipment.

Key document features include:

1) Tools to assist the designer or building owner in determining the best floodproofing option for a particular building including a vulnerability checklist,

 2) Case studies providing examples of applied floodproofing techniques,

3) Equations for determining flood forces and loads,

4) A summary of results from recent dry floodproofing research and testing for new construction.

Link to Floodproofing Non-Residential Buildings – Floodproofing Non-Residential Buildings

 


Dry Floodproofing – Planning and Design Considerations Recovery Advisory

April 2018

The purpose of this Recovery Advisory is to provide guidance on the design of dry floodproofing measures to reduce flood damage and limit interruption of building services.  This advisory incorporates observations made by the FEMA Mitigation Assessment Teams (MATs) in Texas and Florida after Hurricanes Harvey and Irma. 

It describes best design practices and successful implementation of dry floodproofing, as well as lessons learned from failures.  The information in this advisory is directed toward existing and new non-residential facilities. 

Download the Dry Floodproofing – Planning and Design Considerations.