ASFPM 2016: Does Dry Floodproofing Work?
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Adam Reeder co-presented "oes Dry Floodproofing Work?" at the 2016 Association of State Floodplain Managers conference.
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ASFPM 2016: Does Dry Floodproofing Work?
- 1. Does Dry Floodproofing Work? June 22, 2016 Adam Reeder, PE, CFM – CDM Smith Adrienne Sheldon, PE, CFM – AECOM
- 2. Agenda • Some minimum requirements • Reasons for Failures – What are people not getting? • Review of the new FEMA Floodproofing Certificate • How can we reduce future failures?
- 3. Dry Floodproofing Regulatory Requirements • Floodproofing to the BFE • Substantially impermeable below the BFE • Able to withstand hydrostatic loads (lateral and buoyancy loads) • Non-residential (few exceptions) • PE or RA develop and/or review the structural design, specifications, plans, and certify that design and methods of construction meet accepted standards of practice • Certificates recorded with the community
- 4. Dry Floodproofing Insurance Requirements • Floodproofing must extend to the BFE + 1 foot • Higher premiums for active floodproofing measures, lower premiums for passive floodproofing measures Does not meet the CFR Req.
- 5. Failure to Deploy Active Dry Floodproofing Measures • Are they being deployed for every necessary event? – Any event above the FFE regardless of the severity of the flood • What is required to deploy all the shields? – Is any special equipment needed?
- 6. Lack of Basic Maintenance • New penetrations though dry floodproofed wall systems • Deteriorated gaskets • Incorrectly stored shields • Pumps not tested
- 7. Lack of Designer Understanding • What does substantially impermeable mean? • Making wall systems substantially impermeable – CMU and cast-in- place • Using system components that are “certified” for other hazards (Miami-Dade or “weather-proof”) • Little manufacturer feedback on whether a material is appropriate for floodproofing applications
- 8. Lack of Designer Understanding (cont.) • Considering buoyancy forces • Joints and seals that are not designed for hydrostatic forces • Lack of long-term power supply (How many hours can the pump run?) • Temporary Barrier Systems (not structurally connected) • Wooden Shields without gaskets
- 9. Getting the Level of Protection Correct Office Building • 16,000 sf Building • 3 feet of floodproofing • Doors: 2 double glass doors and one single glass door • Windows: 12 windows about 3 feet wide each • Assuming an offset gap between the shields and windows about 6 inches • 1 inch overtopping Results • Overflow Rate: +4 cfs about 1,834 GPM and 110,000+ GPH • Duration to fill the space is: 196 minutes
- 10. Overlooked Requirements • Dry Floodproofing requires a means to remove what water does accumulate • For areas where seepage is expected, flood-resistant materials are to be used • Resistance of lateral hydrostatic loads AND buoyancy needs to be factored into design
- 11. Some Thoughts on Freeboard • Remember the Base Flood Elevations are rounded to the nearest foot • Once a building overtops it is almost impossible to pump out • Overtopping damages will be the same as if nothing was done • We should consider future conditions: – Age of the maps – Development – Sea Level Rise (SLR is a stillwater elev. and waves will increase that value)
- 12. Transfer of Building Ownership • Limited or no communication about the dry floodproofing system • New owners may not understand the necessary steps – Warning Time – Manpower Needs – Evacuation Requirements – Maintenance of the system – Importance of maintaining the waterproofing
- 13. Floodproofing Certificate - 2015 • Certify designed and constructed to meet ASCE 24 and 44 CFR 60.3 (c)(3) • Photographs of components • Maintenance Plan
- 14. Should Dry Floodproofing Continue? Retrofitting existing buildings • Larger buildings in urban, densely developed areas • Building life cycles upwards of 50 years • Elevating may not be feasible • Elevating limits street level access
- 15. Should Dry Floodproofing Continue? New construction • Urban areas where street level access is needed • Experienced designers • Educated/experienced regulators • Buildings with dedicated maintenance staff – Maintenance and awareness of system – Means of passing this on as maintenance staff and ownership changes
- 16. Other Considerations • Dry Floodproofing works best where lower flood depths are anticipated – Hydrostatic forces – Overtopping results in less damage • Flood warning time • Regular review and update of maintenance plan • FEMA is considering regular “recertification”
- 17. Should there be Additional Requirements? • Periodic recertification (under consideration) which should include updates to maintenance plan and current photos of components • Education for designers AND regulators is essential • Insurance claims payments based on level of design event? • Performance standard for dry floodproofing products?
- 18. Questions?
Editor's Notes
- Although NFIP regulations require non-residential buildings to be watertight and protected only to the BFE for floodplain management purposes (to meet NFIP regulations), protection to a higher level is necessary for dry floodproofing measures to be considered for NFIP flood insurance rating purposes. Because of the additional risk associated with dry floodproofed buildings, to receive an insurance rating based on 1-percent-annual-chance (100-year) flood protection, a building must be dry floodproofed to an elevation at least 1 foot above the BFE. Insurance premiums will be lower if dry floodproofing extends higher than the BFE + 1 foot. Dry floodproofed buildings with active floodproofing measures and requiring human intervention are subject to higher insurance premiums than dry floodproofed buildings with completely passive floodproofing measures that do not require human intervention.
- These are specific to insurance though most of the FPM requirements apply here too. Although NFIP regulations require non-residential buildings to be watertight and protected only to the BFE for floodplain management purposes (to meet NFIP regulations), protection to a higher level is necessary for dry floodproofing measures to be considered for NFIP flood insurance rating purposes. Because of the additional risk associated with dry floodproofed buildings, to receive an insurance rating based on 1-percent-annual-chance (100-year) flood protection, a building must be dry floodproofed to an elevation at least 1 foot above the BFE. Insurance premiums will be lower if dry floodproofing extends higher than the BFE + 1 foot. Dry floodproofed buildings with active floodproofing measures and requiring human intervention are subject to higher insurance premiums than dry floodproofed buildings with completely passive floodproofing measures that do not require human intervention.
- While not specifically called out in the CFR, TB-3 indicates a need for a means to remove accumulation AND for areas where seepage is expected, the use of flood-resistant materials. ASCE 24 is now referenced as a requirement in the floodproofing certificate. It does spell out these requirements clearly.
- Written certification that all portions of the structure below the BFE that will render it watertight or substantially impermeable to the passage of water and must perform in accordance with Title 44 Code of Federal Regulations (44 CFR 60.3 (c)(3)) Photographs of shields, gates, barriers, or components designed to provide floodproofing protection to the structure Maintenance Plan should address Exterior envelope of the structure All penetrations to the exterior of the structure All shields, gates, barriers, or components designed to provide floodproofing protection to the structure All seals or gaskets for shields, gates, barriers, or components Location of all shields, gates, barriers, and components as well as all associated hardware, and any materials or specialized necessary to seal the structure.
- Higher flood depths mean stronger walls and heavier building weight and anchoring needed to resist buoyancy 3 feet of damage looking at an average of <25% damage, 8 feet often 40 – 70% damage