In Charleston, we deal with a lot of flooding, sometimes even on sunny days. 

The historic district is surrounded by water on three sides and Charleston has over 90 miles of coastline. FEMA’s National Flood Insurance Program (NFIP) has created flood maps to help determine which properties are in danger of flooding.  In addition, these organizations provide a lot of guidance for renovations and construction within flood zones. Let’s breakdown how to know if you’re in a flood zone and how to get an elevation certificate in Charleston, SC if you need one.

Are you in a Charleston flood zone?

First, go to the FEMA map center website to see if you are in a flood zone (search by street address and zip code).  If your property is in a flood zone, it is important to have a flood elevation certificate.

If you have no idea what that is, you’re in the right place! According to the FEMA & NFIP website floodsmart.gov, “an elevation certificate shows how high a building is compared to how high local floodwaters are expected to get. It includes information like your home’s location, characteristics, and its First Floor Height. First Floor Height is the height of the first (lowest) floor above the ground.”

The elevation certificate helps ensure buildings and any construction projects meet local flood safety requirements. The elevation certificate will be required when you submit for a construction permit (renovation or new construction) if your property is in a flood zone.

It’s also typically required for flood insurance. If your house exceeds the flood requirements, you may even get a discount on the insurance!

Imaged Credit: Fema.gov

If you don’t have a certificate, a licensed land surveyor or engineer can provide a new elevation certificate.  This could cost around $500 (varies depending on the surveyor and location), but it is money well spent if you have flood insurance or you’re planning a renovation or addition.  

In Charleston, it is important to have a flood elevation certificate dated after January 29, 2021, when the flood maps were updated.  At that time, the datum used for the height of land above sea level also changed, rendering the older elevation certificate obsolete.

Here are a few common phrases you’ll find on an elevation certificate:

• Mean Sea Level (MSL) is the average level of the water between low and high tides. If the tide charts say we’re having an 8ft tide, that would be 8 feet above the mid-level between tides, or 8ft MSL.
• Base flood elevation (BFE) is “the anticipated height of water during a flood that has a 1% chance of occurring in any given year, also known as a 100-year flood” per FEMA.
• Design flood elevation (DFE) is the base flood elevation (BFE) plus the required freeboard prescribed by the city or town having jurisdiction over the property.
• Freeboard is a safety factor used when building to provide a buffer above the anticipated flood level. This safety factor affects the Community Rating System by NFIP (how stringent or safe a city is related to flooding), which in turn affects flood insurance premiums for all of us.  The City of Charleston requires a 2-foot freeboard for new construction, and a one-foot freeboard for existing residences.

What information does the elevation certificate provide?

• Section A: existing flood vents, garages, building diagram/type
• Section B: your flood zone and elevation, the flood map number, and datum, as a baseline.
• Section C: existing conditions of the building and adjacent grade.

Section A provides an important reference in line A7, the Building Diagram Number.  See pages 17-19 of the sample elevation certificate with instructions.   

This building diagram will be important when we come to Section C of the form, because it helps us understand which levels the surveyor used as the lowest floor and next higher floor.  The building diagrams are included in the elevation certificate instructions, showing buildings on a slab, on a crawlspace, or on stilts, for example.  In addition, Section A will list information about attached garages and flood openings or vents in crawlspaces.

Section B of the form tells us what flood zone the property is in. The options include X, A, Coastal A, and V, listed from safest to highest flood risk. This section will also tell the elevation for the flood zone, in feet. This is your Base Flood Elevation (BFE). Your property might be AE-10, meaning A flood zone with an elevation of 10 feet.  In that case, the DFE in the City of Charleston is 11 feet for existing homes and 12 feet for new construction.

Section C gives us information about the existing building on this property, including:

• The top of the lowest finished floor: This number is related to mean sea level. You’ll need the building diagram number to know if this lowest floor is a crawlspace, garage, or the main living level.
• The next higher floor: If your building diagram number refers to the lowest level as the crawlspace or garage, the “next higher floor” is your first level of living space.
• Lowest & highest adjacent grade: This is useful info to understand if your lowest floor is below grade, from a drainage perspective. It’s also helpful if you want to know your general ground level for new construction purposes.

What do these numbers mean? 

The critical point is to understand the height of the house’s lowest floor of living space above MSL. This may be the lowest finished floor or the next higher, depending on the building diagram and if the lowest refers to a crawlspace or garage. Ideally, the height of this lowest floor of living space is at least one foot higher than the base flood elevation listed in Section B. 

What if the property has two flood zones, with the line running through the middle of the building?

If your property or building happens to fall right on a line delineating two flood zones, the more stringent flood zone prevails.  For example, if the building overlaps a VE-13 and an AE-12, the building must meet all the requirements for the VE-13 zone. 

What do all the letters mean?

• SFHA: Special Flood Hazard Area
• LiMWA: Limits of Moderate Wave Action. This is a line on the maps that delineates certain parts of the A flood zones as “Coastal A”.
• A: The base floodplain was mapped by approximate methods. BFEs are not determined.
• AE: The base floodplain where BFE is provided on the FIRM in parentheses. i.e. “AE(12)”. The AE flood zone is inclusive of the Coastal A Zone within the LiMWA line.
  • The “E” means an elevation is provided for the zone.
  • Coastal A: Zones that are within the LiMWA line. These have additional regulations, similar to VE flood zones.
• AO: The base floodplain with sheet flow, ponding, or shallow flooding. Base flood depths (feet above ground) are provided.
• AH: Shallow flooding base floodplain. BFEs are provided.
• V: Coastal area subject to a velocity hazard (wave action greater than 3 ft.) where BFEs are not determined on the FIRM.
• VE: Coastal area subject to a velocity hazard (wave action greater than 3 ft.) where BFEs are provided on the FIRM.
• Shaded X (outside of SFHA): Area of moderate flood hazard, usually between the limits of the 1% annual chance flood (base flood or “100-year flood”) and the 0.2% annual chance flood (“500-year flood”) event.
• Unshaded X (outside of SFHA): Area of minimal flood hazard, usually at an elevation greater than the 0.2% annual chance flood (“500 year flood”) event.

(Definitions courtesy of City of Charleston “know your flood zone” website)

FEMA and the NFIP provide a lot of guidance for construction and renovation in flood zones.  For more specific information, check out the NFIP Technical Bulletins. 

I know this is a lot of information to take in! If you have questions, you can always email me. Soon, we’ll release part two of this blog, where I’ll talk more about what you can and can’t do to your property based on the flood zone.  We’ll also discuss the dreaded FEMA 50% rule.