If you live in a flood zone and have not properly vented your crawlspace or garage you are probably paying high flood insurance cost. Also, your home is at higher risk for damage in the event of a flood. If you have a current E.C. (elevation certificate) this will provide the information needed to start getting you home FEMA compliant. If you or your flood insurance company does not have a current elevation certificate. You need to get one from a local surveyor because your annual insurance cost is based on the information on the E.C. Most home owners start wet-floodproofing their own by installing engineered flood vents.
Studies have shown during a flood hydrostatic pressure, the weight of standing water, increases as water fills the crawlspace or garage. Installing engineered flood vents lets the water pass freely in and out of the enclosed area helping the structure to maintain its integrity. Remember, if your home has an attached garage it will need to be properly vented like your crawlspace.
Here is a link to FEMA.gov site for some defintions to help understand flooding and your home: