The speed and volume of floodwaters are powerful enough sometimes to whisk away people and cars and topple buildings. When the pressure of a flood tide against a house becomes too great in comparison to the pressure on the inside, walls will buckle, and the foundation will be destroyed. To help prevent that from happening, there are two primary methods for protecting a house from flooding, depending on its structure.
When you think about keeping flood waters out of a house, the effect of dry floodproofing is probably what comes to mind. Dry floodproofing involves blocking water from entering the house at all. This is largely accomplished by coating the foundation in waterproof sealants or plastic sheeting [source: Kane County Division of Environmental Management]. Doors and windows below the flood plain elevation must also be sealed.
Not all houses are suitable for dry floodproofing because hydrostatic pressure from the water may cause extreme external damage. For that reason, only those built on a concrete slab without basements or cellars are appropriate for dry floodproofing. Brick homes are also more appropriate for it than those with wood siding since they can withstand more pressure [source: Parker]. However, according to the Federal Emergency Management Agency (FEMA), most housing will succumb to floodwaters higher than 3 feet (0.9 meters).
Wet floodproofing, on the other hand, allows some surface water to enter the house. This option may seem counterintuitive, but it can actually decrease the amount of overall damage by balancing the hydrostatic pressure inside and outside of the house [source: FEMA]. This type of design is best utilized for houses with basements. Inside, appliances such as washing machines, water heaters and furnaces should be elevated above the flood level [source: Kane County Division of Environmental Management]. Concrete block walls and bare flooring leave nothing valuable at stake if the floodwaters enter.
Sump pumps installed in the basement can also gird the foundation from water damage. Situated in a sump pit, the pump draws in the groundwater around the house and directs it away from the structure through drainage pipes. Some local ordinances require houses to be outfitted with sump pumps. In emergency situations, external barriers can also effectively stave off floodwater. Whether cement flood walls or improvised levees made of sand bags, strategically placed obstacles can halt the flow toward the house. Shields made of plywood, metal or thick plastic block vulnerable doors and windows.
Each year, floods sweep away thousands of buildings, possessions and precious mementos. With planning and foresight, your homestead doesn't have to be part of that tide of loss.