Cal. Civ. Code § 913
A builder or his or her representative shall acknowledge, in writing, receipt of the notice of the claim within 14 days after receipt of the notice of the claim. If the notice of the claim is served by the claimant's legal representative, or if the builder receives a written representation letter from a homeowner's attorney, the builder shall include the attorney in all subsequent substantive communications, including, without limitation, all written communications occurring pursuant to this chapter, and all substantive and procedural communications, including all written communications, following the commencement of any subsequent complaint or other legal action, except that if the builder has retained or involved legal counsel to assist the builder in this process, all communications by the builder's counsel shall only be with the claimant's legal representative, if any.
Ca. Civ. Code § 913