Gregory Wilson, CFM Adrienne Sheldon, PE, CFM Amit Mahadevia FEMA 259 Update Engineering Principles and Practices for Retrofitting Flood-Prone Residential Structures

2 Engineering Principles and Practices for Retrofitting Flood-Prone Residential Structures FEMA P-259 Provides guidance for selecting and implementing flood retrofitting measures that are feasible and cost effective. Describes: Elevation Relocation Barriers (floodwalls and levees) Dry floodproofing Wet floodproofing

3 Organization of the Design Manual

4 Elevation Structure is raised so lowest floor is at or above the Design Flood Elevation (DFE) Protects structure from damage in a base flood Base flood elevation (BFE): Flood having a 1-percent chance of being exceeded in any given year. Design flood elevation (DFE): Regulatory flood elevation adopted by a local community. Typically, the DFE is the BFE plus any freeboard adopted by the community. FEMA P-55, Figure 2-14

5 Residential structures that can be elevated Houses over a crawlspace Elevated on either solid or open foundation walls Houses over basements Elevated on either solid or open foundation walls Houses on piers, post, piles, or columns Temporary relocation of home may be necessary Slab-on-grade houses Wood frame vs. masonry; different elevation methods Harder Easier

6 Elevation on Solid Perimeter Foundation Walls Before After

7 Elevation on Piers Cross-section of elevated wood-frame house on new or extended pier foundation

8 Elevation on Posts and Piles Posts Piles

9 Relocation Structure is moved to a location less prone to flooding and flood- related hazards

10 Relocation Process Most structure types can be moved as a whole or in segments

11 Select New Site (Step 3) Examine potential sites for: Location outside of floodplain Utility extension feasibility Accessibility for both the house movers and the new site construction crews Permitting feasibility for the existing house on the new lot

12 Prepare the Structure (Step 6) Disconnect utilities Cut holes in foundation wall for beams Install beams Install jacks Install bracing Separate structure from foundation Structure is separated from its foundation (photograph courtesy of Wolfe House Movers)

13 Preparing the New Site (Step 7) Design foundation Design utilities Excavate and prepare new foundation Construct support cribbing Construct foundation walls New foundation wall construction begins (photograph courtesy of Wolfe House Movers)

14 Move the Structure (Step 8) Trailer wheel sets are placed beneath the lifting beams (photograph courtesy of Wolfe House Movers)

15 Dry Floodproofing The portion of a structure below the flood protection level (walls and other exterior components) is sealed to make it impermeable to floodwaters

16 Dry Floodproofing Examples Watertight shields for doors and windows Reinforced walls Membranes and sealants Drainage collection systems and sump pumps Check valves Anchoring

17 Select and Design Sealant System Selection centers on the ability of the manufacturer’s product to be compatible with the length and depth of flooding expected as well as the type of construction materials used Processes for selection of the following systems are presented in the manual Coatings Wrapped Systems Brick Veneer Systems

18 Select and Design Shield System Selected material must be able to: Structurally secure the opening Be compatible with existing construction materials Be responsive to the duration and depth of flooding expected

19 Select Drainage Collection Systems Typical sump detail Underdrain systems: reduce flood loads for short duration flooding by moving floodwater away from building foundation Sump Pumps: used to prevent accumulations of water within residence, typically around important utilities

20 Select Backflow Valves & Emergency Power Backflow valves: helps prevent backflow through sanitary sewer and/or drainage systems Emergency power: if used, observe proper guidelines

21 Dry Floodproofing Pitfalls Active mitigation Increases buoyancy Increases lateral forces potential Potential for total house failure Power dependency (sump pump) Maintenance requirements

22 Wet Floodproofing Involves modifying structure to allow floodwaters to enter in such a way that damage is minimized

23 Wet Floodproofing Concepts FEMA 259 discusses the following concepts related to wet floodproofing: Protecting the structure Designing openings for intentional flooding of enclosed areas below the DFE Use of flood-resistant materials below the DFE Adjusting building operations and maintenance procedures Emergency preparedness for actions that require human intervention Designing protection for the structure and its contents, including utility systems and appliances

24 Use of Flood Resistant Materials All materials exposed to floodwater must be: Durable Resistant to flood forces Retardant to deterioration caused by repeated exposure to floodwater

25 Protecting Utility Systems Electrical systems Heating, ventilation, and air conditioning (HVAC) systems Fuel supply/storage systems Sewer systems Water systems

26 Floodwalls and Levees

27 Floodwall Design Types of floodwalls include: Gravity wall Cantilever wall Buttress Counterfort

28 Levee Home protected by a levee Levee: A manmade compacted earthen structure built parallel to a waterway to contain, control, or divert the flow of water. System may include non-earthen components, such as floodwalls, floodgates, and pump stations.

29 Levee Design Standard levee design criteria was established to provide a conservative design while eliminating several steps in the USACE design process, thereby minimizing design cost

30 Relative Costs and Risks of Floodproofing Methods FEMA 259, Table 3-5

31 Engineering Principles and Practices for Retrofitting Flood-Prone Residential Structures FEMA P-259 An important resource for engineers, architects, and local code officials in flood-prone areas since the first edition was published in 1995.

32 FEMA Building Science Flood/Wind Building Science Helpline:

33 Questions?