Historically, designers have relied on minimum design requirements for building elevations. For more than 50 years, many countries have relied on the 100-year flood elevation, or 1% annual chance flood event, which has a 39 percent chance of being equaled or exceeded over a 50-year period. Through the years many jurisdictions have improved upon this standard by requiring the 100-year flood elevation plus 300 mm. However, because this approach provides variable levels of protection depending on floodplain characteristics, the 2024 edition of American Society of Civil Engineers (ASCE) 24, Flood Resistant Design and Construction, now requires most buildings to be constructed to the 500-year flood elevation, corresponding to a 10 percent chance of exceedance over 50 years. For riverine buildings, however, this requirement does not account for future conditions, meaning the actual likelihood of flooding may be higher than 10 percent over 50 years. This raises the question of whether owners will fully consider their risk tolerance when buildings are constructed.

This presentation will discuss the recently released ASCE 24-24 elevation requirements as an example of a more progressive risk reduction design approach. It will address how designers can effectively discuss risk tolerance with owners and appropriately document owner decisions when evaluating whether increased elevation requirements are warranted. These risk tolerance considerations may include potential physical damages, operational downtime, long-term insurability, and impacts to financing or credit ratings. Examples will be provided to illustrate different approaches to assessing flood risk and determining appropriate elevations, as well as how the selection of mitigation measures can influence overall risk tolerance.