a. Conditions Requiring Curbs. Curbs shall be required under any of the following conditions:
1. The subdivision is within an R-20 district or a district having a smaller lot size;
2. The grade of the street is less than one (1%) percent or more than six (6%) percent;
3. The street frontage between adjacent sections of curb is less than five hundred (500') feet;
4. The subdivision is for commercial or industrial purposes.
b. Block Requirements. If curbs are required in any portion of a block within the subdivision, the entire frontage along that block shall be curbed.
c. Minimum Grade. The minimum grade for curbs and gutters shall be one (1%) percent except a reduction may be authorized by the Engineering Department.
d. Designation on Improvement Plans. Improvement plans shall show curb profiles, including profiles for all curb returns and cul-de-sacs.
e. Minimum Elevations. Minimum top of curb elevations shall conform to Section 31-28.