Flood Zones Explained: Zone X, A, AE and D for LA County Land

FEMA draws these zones on its Flood Insurance Rate Maps. Here is what each one found on LA County vacant land means:

Zone X is FEMA's moderate-to-minimal flood risk area. Unshaded X is outside the 500-year floodplain; shaded X has a 0.2% chance of flooding in any year, shallow 1% flooding under a foot deep, or levee protection. Federal rules do not require flood insurance in zone X.

138,293 of LA County's vacant lots are zone X, about 82% of them.

Zone AE is a high-risk area with a 1% chance of flooding in any year, where FEMA has calculated the base flood elevation. New buildings must have their lowest floor at or above that elevation, and a mortgage from a federally regulated lender on a building there requires flood insurance.

Zone A is the same 1% risk, but without a calculated flood elevation, so you may need a surveyor or engineer to work one out before you build. Zones AO and AH mark shallow flooding, often 1 to 3 feet deep, from sheet flow down slopes or ponding.

Zone D means FEMA has not studied the area, so the flood risk is unknown. It is not a sign that the land is safe. Much of the high desert in north LA County is zone D.

The most zone D lots are in Acton (582), Lake Hughes (233), Green Valley (230), Northridge (217) and Palmdale (194).

Flood insurance covers buildings and their contents, not the land itself, so it is not required on an empty lot. Once you build in a high-risk zone (A or V) and borrow from a federally regulated or insured lender, flood insurance on the building is required.

Usually yes, with conditions. LA County takes part in the National Flood Insurance Program, so a new building in a high-risk zone needs a floodplain permit, and its lowest floor must sit at or above the base flood elevation. That can mean raising the pad, building on piers, or engineering for flood flow, which adds cost. Some lots, such as those in a regulatory floodway, may not be buildable at all. LA County Public Works handles floodplain permits in unincorporated areas; cities handle their own.

Every LandGrab parcel page shows its FEMA zone near the top. The official source is FEMA's Flood Map Service Center, where you can look up an address and download the map panel. Maps get revised through Letters of Map Revision, so check the date on the panel.

Each city page lists lots inside and outside the flood zone. See also the fire hazard zone guide.