Wet Vs. Dry Floodproofing Non-Residential Buildings

Weather and climate experts have forecasted Atlantic hurricane activity in 2021 to be above average. Even without devastating straight-line winds and spawned tornadoes, flooding is a very real possibility for structures across the Sunshine State. Due to the state’s unique vulnerability to storm surges and other flooding events, Florida and local building codes have robust floodproofing requirements for non-residential buildings.

The two major types of floodproofing strategies are, somewhat ironically, wet and dry floodproofing. In a nutshell, dry floodproofing involves implementing flood-resistant components to a structure that repel flood waters and make the structure more or less impermeable. Conversely, wet floodproofing allows flood waters to enter lower portions of a structure that may become wet without major consequences.

Dry floodproofing definitely sounds better, right? Well, as we discuss below, it’s a bit more complicated.


To help determine whether a structure needs dry or wet floodproofing, you first need to assess the base flood elevation (BFE) and design flood elevation (DFE) in your area. The base flood elevation is the level at which a 100-year flood is expected to reach. In other words, the most significant flooding event each year has a one percent chance of reaching the base flood elevation.

The design flood elevation is the highest elevation at which new buildings (and buildings that are substantially refurbished) have been prepared for flooding damage. Design flood elevation is usually a few feet (perhaps just one) above base flood elevation.

In certain flood zones, non-residential buildings that are at least partially located below the base flood elevation (BFE) are required to be outfitted with dry floodproofing components. However, FEMA and the National Flood Insurance Program require some structures to have wet floodproofing. 

How Does Wet Floodproofing Work?

One of the main reasons wet floodproofing is often used is that it is less expensive than dry floodproofing. Wet floodproofing involves clearing a space under a structure where flood waters can occupy without corroding the foundation or other essential systems. The areas where flood waters would occupy need to have special materials that allow easy cleaning after the waters subside. Walls should be easily drainable, and all appliances should be placed above the DFE. 

How Does Dry Floodproofing Work?

The concept of dry floodproofing is fairly straightforward. Experts apply water-resistant materials along the exterior walls of a structure in order to keep out all water. This process is more labor- and parts-intensive than wet floodproofing. It also exposes the structure to substantial hydrostatic pressures, which is not the case with wet floodproofing. Spreading out flood waters under a structure dramatically reduces lateral loads.


In many cases, project owners and developers are legally bound to implement a particular floodproofing method. We can help you figure out the best method for your project and make sure the structure is safe and compliant. For professional structural engineering services from a caring team, call our team at (305) 666-0711 today.

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