FLOOR BASE COURSE
Floors of basements, except as provided for in Section 1807.1.1, shall be placed over a floor base course not less than 4 inches in thickness that consists of gravel or crushed stone containing not more than 10 percent of material that passes through a No. 4 (4.75 mm) sieve.
EXCEPTION: Where a site is located in well-drained gravel or sand/gravel mixture soils, a floor base course is not required.
This section implies that a base course a minimum of 4 inches thick is required under all basement floors. The base course shall consist of gravel or crushed stone that does not allow more than 10 percent passage through a No. 4 sieve, which is 4.75 mm.
The only exception to this is if the basement floor is located in an area that is well drained through gravel or a sand and gravel mixture.
Section 1807.1.1 defines a basement as “a basement is considered a story above grade plane if any portion of the basement wall is located above the ground level.”