Search the building code.

• R408

  Under-Floor Space

  International Residential Code, 2024 · Chapter 4, FoundationsRead the full text (opens UpCodes in a new tab)

• R408.1

  Moisture Control

  International Residential Code, 2024 · Chapter 4, FoundationsRead the full text (opens UpCodes in a new tab)

• R408.2

  Openings for Under-Floor Ventilation

  • Vented crawl spaces need 1 sq ft of opening per 150 sq ft of floor, with one vent within 3 ft of each corner, screened to 1/4 in or less.

  International Residential Code, 2024 · Chapter 4, FoundationsRead the full text (opens UpCodes in a new tab)

• R408.3

  Unvented Crawl Space

  • Unvented crawl spaces cover the ground with sealed Class I vapor retarder (6 in laps, 6 in up the walls) and get exhaust, conditioned air at 1 cfm per 50 sq ft, plenum use or a dehumidifier.

  International Residential Code, 2024 · Chapter 4, FoundationsRead the full text (opens UpCodes in a new tab)

• R408.4

  Access

  • Every under-floor space has access: at least 18 x 24 in through the floor or 16 x 24 in through a wall, with an areaway if below grade, and never under a door.

  International Residential Code, 2024 · Chapter 4, FoundationsRead the full text (opens UpCodes in a new tab)

• R408.5

  Removal of Debris

  • Clear vegetation and organics under the floor, and remove wood forms and debris before occupancy.

  International Residential Code, 2024 · Chapter 4, FoundationsRead the full text (opens UpCodes in a new tab)

• R408.6

  Finished Grade

  • Crawl space grade may be at footing bottoms, but must match outside grade where water could rise within 6 in of the floor or doesn't drain, unless drained.

  International Residential Code, 2024 · Chapter 4, FoundationsRead the full text (opens UpCodes in a new tab)

• R408.7

  Flood Resistance

  • Crawl spaces in flood zones get flood openings and an inside grade at or above outside grade on at least one side.

  International Residential Code, 2024 · Chapter 4, FoundationsRead the full text (opens UpCodes in a new tab)

• R408.8

  Under-Floor Vapor Retarder

  • In warm-humid zones 1A, 2A and 3A, floor insulation over a vented crawl space carries a vapor retarder of 1.5 perms or less on its exposed face.

  Local review: San Antonio (Bexar County) is climate zone 2A, so this applies to vented crawl spaces there.

  International Residential Code, 2024 · Chapter 4, FoundationsRead the full text (opens UpCodes in a new tab)

Searches all 4,276 IRC 2024 sections, 5,532 IBC 2024 sections and defined terms (Chapters 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33 so far) and each city's local rules as they are added. Section numbers and titles from the International Residential Code and International Building Code, 2024 editions, copyrighted by the International Code Council; the IRC's electrical chapters (34 to 43) follow NFPA 70, the National Electrical Code. Requirements are summarized in our words (IRC Chapters 3 to 43, IBC Chapters 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33); read the full text at the link on each result. Local values come from each city's published documents.