1907A Slabs-on-Ground — 2025 California Building Code

1907 A .1 Structural slabs-on-ground. Structural concrete slabs-on-ground shall comply with all applicable provisions of this chapter. Slabs-on-ground shall be considered structural concrete where required by ACI 318 or where designed to transmit either of the following:

1. Vertical loads or lateral forces from other parts of the structure to the soil.
2. Vertical loads or lateral forces from other parts of the structure to foundations.

CONCRETE

1907 A .2 Nonstructural slabs-on-ground. Nonstructural slabs-on-ground shall be required to comply with Sections 1904 A .2, 1907 A .3 and 1907 A .4. Portions of the nonstructural slabs-on-ground used to resist uplift forces or overturning shall be designed in accordance with accepted engineering practice throughout the entire portion designated as dead load to resist uplift forces or overturning. 1907 A .3 Thickness. The thickness of concrete floor slabs supported directly on the ground shall be not less than 3 1/2 inches (89 mm).

1907 A .4 Vapor retarder. A 6-mil (0.006 inch; 0.15 mm) polyethylene vapor retarder with joints lapped not less than 6 inches (152 mm) shall be placed between the base course or subgrade and the concrete floor slab, or other approved equivalent methods or materials shall be used to retard vapor transmission through the floor slab.

Exception: A vapor retarder is not required:

1. For detached structures accessory to occupancies in Group R-3, such as garages, utility buildings or other unheated facilities.

2. For unheated storage rooms having an area of less than 70 square feet (6.5 m [2] ) and carports attached to occupancies in Group R-3.

3. For buildings of other occupancies where migration of moisture through the slab from below will not be detrimental to the intended occupancy of the building.

4. For driveways, walks, patios and other flatwork that will not be enclosed at a later date.

5. Where approved based on local site conditions.