National Flood Docs

Your glossary for all things flood related.

Building Types

Flood insurance rating gets easier once you know which of the main three building types your structure is.

Building Types

Slab on Grade: Diagrams 1a, 1b, and 3

Slab on Grade

Garages Attached to Slab-on-Grade Buildings:

The attached garage could only be excluded as the LFE if all of the following conditions are met:

  • The building is described and rated as a single family dwelling
  • Building is located in an A Zone.
  • The garage floor is below the top of the bottom floor, and
  • The garage has proper flood openings, regardless of whether there is or isn’t machinery and equipment below the BFE

Basements: Diagrams 2a, 2b, and 4

Basements 101:


According to FEMA, a basement is any area of the building, including any sunken room or sunken portion of a room, having its floor below ground level (subgrade) on all sides.

💡 Remember: A basement is a basement regardless of its use (living, working, storage, etc.).

Elevated: Diagrams 5 & 6

Elevated Daigrams 5 & 6

A Zones: If an enclosure is below the BFE and is used only for building access, vehicle parking, or storage, and has proper flood openings, then the enclosure may be excluded as the LFE. V zones: Breakaway walls are not a part of the structural support of the building and are designed to collapse during a flood without causing damage to the foundation or the elevated portion of the building.

💡 Note: In V Zones, breakaway enclosures measuring less than 300 square feet resulting in a lower premium.

Elevated: Diagrams 7, 8, and 9

Elevated Daigrams 7, 8, & 9

Vinyl or aluminum skirting that you see around a manufactured home is not an enclosure for rating purposes. However, if the manufactured home sits on solid foundation walls, it can affect the LFE for rating.