Course Overview

This course provides an introduction to engineering design and economic guidance about what constitutes technically feasible and cost-effective retrofitting measures for flood-prone residential structures.

Objectives: At the end of this course, you will be able to:

  • Understand regulatory requirements that apply to retrofit projects
  • Describe the technical, regulatory and site-specific parameters to consider in flood protection design
  • Determine flood and other hazards present at the site that would impact design
  • Understand the basic parameters of each retrofitting measure and the associated design practices

This course is only intended to provide an introduction to retrofitting flood-prone residential structures. It is not intended to replace consultation with an engineer or architect.

Lesson List-Introduction to Retrofitting, Regulatory Requirements, Parameters of Retrofitting, Determination of Hazards, Design Practices
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This lesson should take approximately 15-20 minutes to complete.
Unit Objectives

This unit includes a basic overview of the different flood retrofit options. Each option is defined and the pros and cons to each retrofit type are discussed. An overview of the general retrofitting process is also given.

  • List and define the five basic retrofitting measures for flood hazards
  • Explain some of the advantages and disadvantages of each retrofitting measure
  • Describe, in general, the considerations that should be taken when retrofitting
  • Identify the seven steps in the retrofitting process
Lesson List: Introduction to Retrofitting (Starting); Regulatory Requirements; Parameters of Retrofitting; Determination of Hazards; Design Practices
Organization of the Design Manual (FEMA P-259)
IS0280-Organization of the Design Manual: Chapter 1-Intro to Retrofitting, 2-Regulator Requirements, 3-Parameters of Retrofitting, 4-Determination of Hazards, 5-General Design Practices, 5D,E, F, R, W-Types of Flood Retrofits, 5I-Case Studies
Organization of the Design Manual (cont.) (FEMA P-259)
Organization of the Design Manual: Appendix A-Sources of FEMA Funding, App B-Understanding the FEMA Benefit-Cost Analysis Process, App C-Sample Design Calculations, App D-Alluvial Fan Flooding, App E-References, App F-Other Resources, App G- Summary of NFIP Requirements and Best Practices, Appendix H-Acronyms. NOTE: Cross references to sections in the design manual (FEMA P-259) can be found at the bottom left of Key slides
Icons Used in This Training
Retrofitting Methods
Retrofitting measures for flood hazards include:
Retrofitting Methods-Elevation, Relocation, Dry Floodproofing, Wet Floodproofing, Floodwalls/Levees
Elevation (1 of 3)
  • Structure is raised so lowest floor is at or above the Design Flood Elevation (DFE)
  • Protects structure from damage in a Base Flood
  • Elevation techniques include:
    • Elevation on solid perimeter foundation walls
    • Elevation on open foundation systems
  • Must consider other hazards in design (i.e., seismic, wind)
    • Terminology: Base Flood-Base flood is defined as the flood having a 1-percent chance of being equaled or exceeded in any given year. The Base Flood Elevation (BFE) is the elevation to which floodwaters rise during a base flood.
    Terminology: DFE: DFE is the regulatory flood elevation adopted by a local community. Typically, the DFE is the BFE plus any freeboard adopted by the community. The Flood Protection Elevation (FPE) or Flood Protection Level (FPL) is equal to the DFE (or BFE + 1 foot, whichever is higher). This manual uses the DFE.
    Elevation (2 of 3)

    Elevation on solid perimeter foundation walls

    • Used in areas of low to moderate water depth and velocity
    • Structure raised from current foundation, support walls extended
    Graphic of a house with elevation of existing residence on extended foundation walls.
    Elevation (3 of 3)

    Elevation on open foundation systems

    • Vertical structural members (not a continuous foundation wall)
    • Includes piers, posts, columns, and piles
    IS 0280 elevation cont fig 1-3 lrg
    Figure 1-3. Elevation on piers
    IS 0280 elevation cont fig 1-4
    Figure 1-4. Elevation on posts or columns
    IS 0280 elevation cont fig 1-5
    Figure 1-5. Elevation on piles
    Elevation Advantages and Disadvantages
    IS 0280 Elevation Advantages and Disadvantages

    Table 1-1

    NFIP = National Flood Insurance Program; BFE = Base Flood Elevation

    Relocation
  • Involves moving a structure to a location less prone to flooding and flood-related hazards such as erosion
  • Most structure types can be moved as a whole or in segments
    • relocation process:
    Figure 1-8. Structure to be relocated
    Relocation process-Step 1-Select the house moving contractor, Step 2-Analyse the existing site and structure, Step 3-Select, analyze and design the new site, Step 4-Prepare the existing site, Step 5-analyze and prepare the moving route, Step 6-prepare the structure, Step 7-prepare the new site, Step 8-Move the structure, Step 9-Restore the old site.
    Relocation process fig 5R-2
    Relocation Advantages and Disadvantages
    IS 0280 Relocation Advantages and Disadvantages
    Table 1-2
    Dry Floodproofing
    Is the strengthening of existing foundations, floors, and walls to withstand flood forces while making the structure watertight and substantially impermeable to floodwaters
    fig 1-9 Dry floodproofing-Maximum protection level is 3 feet (including), backflow valve prevents sewer and drain backup, shields for opening, external coating or covering impervious to floodwater.
    Figure 1-9. Dry floodproofed structure
    Dry Floodproofing Advantages and Disadvantages
    IS 0280 Dry Floodproofing Advantages and Disadvantages
    Table 1-3
    Wet Floodproofing
    Modifying a structure to allow floodwaters to enter it in such a way that damage to the structure and its contents is minimized
    fig 1-10-Wet floodproofing-Openings provided to let floodwaters enter in the subgrade basement, furnace and other utilities relocated to living area or utility room addition
    Figure 1-10. Wet-floodproofed structure
    Wet Floodproofing Advantages and Disadvantages
    IS 0280 Wet floodproofing table 1-4
    Table 1-4
    Floodwalls and Levees
    The placement of floodwalls or levees around the structure
    fig 1-11-Floodwalls and levees-Floodwall is reinforced and anchored to withstand flood load, Levee is compacted fill with 2:1 or 3:1 slope (for stability), Sump pump removes seepage and internal drainage, backflow valve prevents sewer and drain backup
    Figure 1-11. Structure protected by floodwall and levee
    Floodwalls and Levees Advantages and Disadvantages
    IS 0280 Floods and levees table 1-5
    Table 1-5
    Considerations When Retrofitting

    Some considerations when implementing a retrofitting strategy include:

    • Substantial damage/improvement requirements under the NFIP, local building codes, and floodplain management ordinances
    • Codes, ordinances, and regulations, for other restrictions
    • Retrofitted structures should not be occupied during conditions of flooding
    • Consult professionals for the design and construction of retrofitting measures
    • Maintenance of retrofitting measures should be included in plans
    • Purchase of or continuing flood insurance coverage
    • Plan of action for retrofit requiring human intervention
    Retrofitting Process

    The decision to retrofit is usually a result of:

    • Having witnessed or experienced a flooding event
    • Having sustained substantial damage from a flood or other event
    • Implementing a substantial improvement on the home that requires adherence to floodplain regulations

    Information can be obtained through other homeowners, community officials, contractors, or design professionals

    fig 1-13 Retrofitting Process-Homeowner motivation- homeowner coordination-parameters of retrofitting-determination of hazards-benefit-cost analysis-design-construction-homeowner maintenance
    Figure 1-13. Primary steps in the retrofitting process.