As a lagoon front home owner and Realtor-the answer to your question is an elevation certificate. This is obtained through a licensed surveyor and I recommend every seller to obtain one prior to listing. It will tell you what the current elevation is of the home as well as the flood zone the home is in-
example ; if the home is located in an AE7 zone and the elevation certificate shows the home to be at 6.2 ft- the home is not conforming, If the home were at 6.5ft or higher it would conform.
As for raising of the home- if there was 51% damage to the "building" the local building codes are making it mandatory to elevate your home to conform to FEMA standards. If the home was not damaged or sustained minor damage, and is currently below the FEMA flood elevation, elevating it is not mandatory,however flood insurance rates will be higher as the home is at a higher risk. FEMA does not mandate raising home, they regulate at what elevation they need to be to conform.
ALSO- if the home seller had flood insurance and the home was their primary residence and the home does need to be elevated-they could and should have applied for the FEMA ICC grant of $30,000.00-this grant is only to offset the cost of raising the home to conform to FEMA standards and nothing else, it also runs with the property so if you were to purchase a home that needs to be raised to conform-the $30k grant would go with the property sale and you would be entitled to access it.
If you have any other questions feel free to contact me on my cell
Joseph Jay Scangarella