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Basement Requirements for Residences

This page outlines only the common requirements for residential basements; it does not cover all of the California Building Standards that may apply to basements.

Allowable Uses

A basement is a floor level below the first story in a building that meets a height standard: If the floor-to-ceiling height measures at least 6 feet-8 inches, the space is considered a basement. If the floor-to-ceiling height is 6 feet-8 inches or more but the natural grade of the floor SLOPES more than 2 percent due to hillside topography, the area may be considered an under-floor area due to its non-usability.

Habitable Basement - A habitable basement must have a minimum ceiling height of 7 feet and meet other code requirements.

Non-Habitable Basement - If not intended as habitable space, then the basement may not be finished to look like habitable space, and lighting must be limited to minor general lighting and for servicing any permanently installed HVAC equipment.

An under-floor area or “crawl space” is the area below the first floor if the floor-to-ceiling height is less than 6 feet-8 inches. It may be used ONLY for equipment that services the dwelling, such as a furnace, water heater, or central vacuum system. Plumbing fixtures are not allowed except as they relate to the service equipment. Under-floor areas may not be used an office, workshop, laundry room, bathroom, sleeping area, cooking area, entertainment room, or other similar use. Equipment must be installed so as to provide access for servicing as required by code.

Access, Exits and Escape Routes

Basement Requirements

  • Stairways and ramps must comply with California Residential Code.
  • Provide a code-compliant exit to the outdoors at the required egress door without traveling through a garage.
  • Provide an emergency escape/rescue opening except when basement is 200 sf or less and used only for mechanical equipment.
  • Code does not specify the separation distance of an exit from an emergency escape route in a basement, but it is advisable to separate these means of escape

Under-Floor Requirements

  • Minimum access opening: 18 x 24 inches. If there is service equipment, the opening shall be sized to allow removal of the largest piece of equipment, and may not be less than 22 x 30 inches.
  • Access may be by a ladder, stairway, or ramp and must comply with California Residential Code.
  • Exits and emergency escape routes are not required.

Emergency Escape / Rescue Opening - Required Dimensions

  • The bottom of the clear opening is no more than 44 inches above the floor.
  • Opening minimum height: 24 inches
  • Opening minimum width: 20 inches
  • Opening minimum area: 5.7 sf, or 5 sf IF the sill height is not more than 44 inches below grade

Window Well / Light Well Required Dimensions

  • Minimum area of emergency escape/rescue window wells: 9 sf with a 36-inch dimension and allow emergency escape to fully open.
  • Minimum area of light well: width of window and 36 inches deep
  • Projections in a well are not allowed (excluding ladders, landings, security devices and covers) where such projections restrict required natural light or impede emergency escape/rescue. Projections above the well must provide a minimum overhead clearance of 7 feet measured from grade level.
  • Encroachment of ladders, landings, security devices and covers must be considered in the natural light calculation and the window well must be sized accordingly.

Landings

  • Landings shall be incorporated into the ladder design when a window well exceeds 12 feet in height.
  • The first landing shall be no higher than 12 feet from the standing surface of the window well to the top of the landing.
  • For window wells deeper than 12 feet but less than 24 feet, the landing shall be installed at the midway point of the well.
  • Landings shall not be more than 12 feet apart.
  • Landings shall be a minimum 9 sf with no dimension less than 36 inches.

Guardrails

  • Code-compliant guardrails are required around window wells/light wells when the depth of a well exceeds 30 inches at any point.

Drainage

  • Window wells/light wells subject to rainwater collection must discharge by gravity into drywells or leach fields or by mechanical means such as with lift stations or sump pumps.
  • The floors of window wells/light wells shall be sloped to an approved drain or sump pump.
  • Pumped drainage systems shall discharge to the outside of the building in a manner as approved by the Building Division.

Security Bars, Grilles, Grates and Covers

  • Covers and security devices over emergency escape window wells must be easily operable from the inside of the well without the use of special knowledge, tools, or keys. And, when required by the Building Division, an opening assisting device (such as spring loading) shall be employed.
  • The owner must maintain efficient and smooth operation of all such removable covers and security devices to insure their reliable operation for the life of the cover or device.
  • Covers and security devices are designed to support actual and/or anticipated loads. For example, covers and devices which are accessible to foot traffic and contain “standing surfaces” shall be designed to withstand at least 40 lbs. per sf.
  • The minimum clear opening at grade level for window wells used for emergency escape or rescue shall be 9 sf with a minimum dimension of 36 inches.
  • When a cover or security device is utilized at an emergency escape or rescue well, a permanent sign, as approved by the BO shall be affixed to the home adjacent to the well stating:

Emergency Escape & Rescue Well – Do Not Block

  • When a cover or security grille is used at emergency escape and rescue window wells, it may not be apparent to a person looking up at the cover or device that they can readily exit the window well in an emergency. Therefore, a permanent sign, as approved by the Building Division shall be affixed to the wall adjacent to such windows stating:

Emergency Exit

A PDF handout version of this information is available on our Building Handouts and Forms page.