Cal. Pub. Contract Code § 21152
If any change or addition in the work being performed under a construction contract pursuant to this section is deemed necessary, the board may authorize the contractor to proceed with the change or addition without the formality of obtaining bids therefor, provided that the extra cost to the district shall not exceed five thousand dollars ($5,000) when the total amount of the original contract does not exceed fifty thousand dollars ($50,000), nor 10 percent of the amount of any original contract which exceeds fifty thousand dollars ($50,000). The board may, by board order, authorize the Director of Public Works or other district officer to order such changes or additions in the work being performed, provided that the above conditions are satisfied and that the cost of the change or addition does not exceed twenty-five thousand dollars ($25,000). The authorization to the Director of Public Works or other district officer shall include the authority to grant any contract time extensions necessary in connection with the changes or additions. All changes or additions to the work shall be ordered in writing. If a change or addition in a contract awarded under the provisions of this section is requested by any person, firm, corporation, or public agency, other than the district, which person, firm, corporation, or public agency agrees to pay all of the cost of the change or addition, the board may, by board order, authorize the Director of Public Works or other district officer to direct the contractor to proceed with the change or addition without the formality of obtaining bids therefor, provided that the cost of the change or addition does not exceed 15 percent of the original contract price.
Ca. Pub. Cont. Code § 21152