A homeowners' exemption may also apply to a supplemental assessment. For more information, call (925) 313-7481.STATEMENTS. This claim may be used to file for the Homeowners' Exemption for the Assessment Roll and the Supplemental Assessment Roll. Welcome to the homestead estimated amount page for Single Family Detached homes for Contra Costa county. To qualify for the homeowners' exemption, the home must have been the principal residence of the owner as of January 1 of that tax year. Download PDF BOE-266 REV. Many California families are forgetting to claim a common homeowner tax break. Page form can get you your discount. Exemptions ; 11930, Transfer into or out of a trust. Interests transferred outright to, or in trust for the benefit of any person or entity.