Section 1.1 of ASCE 24 addresses dry floodproofing as a method to render a structure “substantially impermeable (This is echoed in U.S. Army Corps of Engineers [USACE] EP 1165-2-314, Floodproofing Regulations.),” resulting in:
a space free of through cracks, openings, or other channels that permit unobstructed passage of water and seepage during flooding, and which result in a maximum accumulation of [100 mm] 4 inches of water depth in such space during a period of 24 hours.
This requires substantial attention to choice of materials, construction techniques, and testing to meet the stated standard. A floodproofing certificate for nonresidential structures (Office of Management and Budget [OMB] No. 1660-0008) must be signed and sealed by a properly licensed design professional certifying to having developed or reviewed the floodproofing design plans, specifications, as-built drawings for construction, and physical inspection to comply with accepted standards of practice for dry floodproofing (i.e. ASCE 24-05, ASCE 24-14, or their equivalent).
For flood insurance premiums to reflect the additional protection and lower risk, dry floodproofing must extend 0.3 m (1 ft) above BFE. A typical scenario could see an annual NFIP insurance premium go from $38,615 to $4823 with compliant dry floodproofing measures.
The challenge of traditional flood protection solutions
Industry professionals have identified most floodproofing designs experience breaches at opening points. For buildings located in flood-prone areas, only a few flood protection options have been available until recently. Historically, the most common system has relied on stop logs—a system of vertical, slotted posts holding stacks of horizontal rectangular ‘logs’ that can be erected around the building or critical doorways and openings to form a continuous barrier. The most significant issue with stop logs—and similar aluminum-sheet barricade systems—involves the materials’ storage.
These components must be kept onsite in what could otherwise be valuable, revenue-generating space, or they have to be stored offsite, often at some distance from the building they are intended to protect. It can take as long as a week to retrieve the truckloads of materials required to erect a barrier around the perimeter of a typical commercial or government building. Having the necessary labor and equipment at the time of need is also a big concern.
For weather-related events, this can mean having to make a decision whether or not to deploy well before forecast models have reached a consensus about storm paths and severity. Deploying unnecessarily is expensive, but hesitating to deploy to avoid that expense can be catastrophic. Further, because
of the unpredictable nature of some natural disasters, like earthquakes or dam breaks, and terror-related acts that can cause flooding, it can be virtually impossible to retrieve and erect a stop-log or barricade system in time. (The Department of Homeland Security (DHS) Science and Technology Directorate [S&T] is researching technologies that can prevent or limit flooding in transportation tunnels. For more, visit www.dhs.gov/sites/default/files/publications/Resilient%20Tunnel%20Project-508_0.pdf.)
Having experienced this during Superstorm Sandy, New York City now requires an annual deployment of the flood barrier systems to ensure facility maintenance staff are familiar with the systems and their use. This flood drill has always been part of the ASCE 24 standards, which calls for periodic testing of the barrier systems, but now communities are clearly stating the requirement in their floodplain ordinances. This clarification is now driving up the cost of ownership of the systems that need to be retrieved, as they also require extensive labor and equipment to deploy. These are all factors that play into a dry floodproofing system not being deployed in time.