Any contract for roofing materials, or for the installation, repair, or replacement of all or any portion of the roof of a residential structure, including, but not limited to, a manufactured home or mobilehome, shall be in writing if the contract includes any warranty of the materials or workmanship that extends for any period of time beyond completion of the work.
Source:
Section 1797.91, https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=CIV§ionNum=1797.91..