TEXAS WATER DEVELOPMENT BOARD Crawl Spaces and Basements in the Floodplain

Regulations on Crawl Spaces and Basements Foundations in new or substantially improved floodplain structures must meet the following requirements of the National Flood Insurance Program (NFIP): ■ There must be a minimum of two openings with a total net area of at least one square inch for every square foot of enclosed area subject to flooding. ■ The bottom of all openings must be no higher than one foot above grade. Openings may be equipped with screens, louvers, valves, or other coverings or devices, provided that they permit automatic entry and exit of flood waters.

Local laws on floodplain management are based on NFIP regulations. Certain construction features of buildings in floodplains directly affect their flood- insurance rates. In new or substantially improved structures, elevating must be carried out correctly or the structure will face inordinately high premiums. (In most cases, the purchase of flood insurance is mandatory when obtaining financing for construction in a floodplain.) In Texas, due to climate and other considerations, fill is the best method of elevating structures to prevent flood damage. The diagrams on the inside pages show three examples of elevated residences in areas identified as flood prone. The first example meets the NFIP requirements; the second and third do not. For more information on NFIP technical bulletins relating to crawl spaces and basements, contact the Flood Mitigation Planning Division Texas Water Development Board P.O. Box 13231 Austin, TX 78711-3231 (512) 463-6478

Definitions Here are some key NFIP definitions related to crawl spaces and basements: ■ Basement—any area of the building having its floor below ground level on all sides. ■ Lowest floor—the lowest floor of the lowest enclosed area (including the basement).

Exception—An unfinished or flood-resistant enclosure, usable solely for parking of vehicles, building access, or storage is not considered a building’s lowest floor for the purposes of these definitions.

A floor in these definitions may either be finished (concrete) or unfinished (dirt, gravel, sand). FOUNDATION OPENING WITH VENT

BASE FLOOD EVELATION

BOTTOM OF 12" MAXIMUM HEIGHT OPENING ABOVE GRADE

BOTTOM OF Residence MeetS CRAWL SPACE

NFIP RequiFOUNDATIONrements Meets NFIP Requirements— approved construction lowers risk of flooding damage in crawl space, lowering premium.

Residence PROPER OPENINGS

NFIP Requirements LOWEST ADJACENT GRADE REFERENCE LEVEL/LOWEST FLOOR BOTTOM OF CRAWL SPACE

These diagrams show three examples of elevated FOUNDATION OPENING WITH VENT residences in areas identified

as flood prone. BASEBASE FLOOD FLOOD ELEVATION EVELATION

BOTTOM OF 12" MAXIMUM HEIGHT OPENING The first example meets ABOVE GRADE the NFIP requirements; BOTTOM OF Front View CRAWL SPACE the second and third do not. Side View FOUNDATION

Building: one floor with bottom of crawl space at or above lowest adjacent grade Yes

Elevating Foundation: solid perimeter walls Yes

PROPER Enclosure: unfinishedOPENINGS crawl space with proper openings. Yes LOWEST ADJACENT GRADE REFERENCE LEVEL/LOWEST FLOOR BOTTOM OF CRAWL SPACE Meets NFIP Requirements Yes Residence FOUNDATION OPENING FOUNDATION OPENING NFWITHOUTIP VENT Requirements (cont.)WITH VENT BASE FLOOD EVELATION BASE FLOOD EVELATION

BOTTOM OF 12" MAXIMUM HEIGHT OPENING ABOVE GRADE

BOTTOM OF CRAWL SPACE BOTTOM OF Residence does notCRA MeetWL SPACE Residence does not Meet

NFIP RequiFOUNDATIONrements NFIP FOUNDRequiATIONrements Lacks Proper Openings— Bottom of Crawl Space below Grade— Crawl space exposed to greater risk of damage Crawl space exposed to greater risk of damage from flooding, resulting in higher premium. from flooding, resulting in higher premium.

PROPER OPENINGS

LOWEST ADJACENT LOWEST ADJACENT GRADE GRADE REFERENCE LEVEL/LOWEST FLOOR REFERENCE LEVEL/LOWEST FLOOR BOTTOM OF CRAWL SPACE BOTTOM OF CRAWL SPACE

FOUNDATION OPENING FOUNDATION OPENING WITHOUT VENT WITH VENT

BASEBASE FLOODFLOOD ELEVATIONEVELATION BASE FLOOD ELEVATIONEVELATION

BOTTOM OF 12" MAXIMUM HEIGHT OPENING ABOVE GRADE

BOTTOM OF CRAWL SPACE BOTTOM OF Front View CRAWL SPACE Front View Side View Side View FOUNDATION FOUNDATION

Building: one floor with bottom of crawl Building: one floor with bottom of crawl space at or above lowest adjacent grade Yes space at or above lowest adjacent grade NO

Elevating Foundation: Elevating Foundation: solid perimeter walls Yes solid perimeter walls Yes

PROPER Enclosure: unfinished crawl space Enclosure: unfinishedOPENINGS crawl space with proper openings. NO with proper openings. Yes LOWEST ADJACENT LOWEST ADJACENT GRADE GRADE REFERENCE LEVEL/LOWEST FLOOR REFERENCE LEVEL/LOWEST FLOOR BOTTOM OF CRAWL SPACE BOTTOM OF CRAWL SPACE Meets NFIP Requirements NO Meets NFIP Requirements NO