Short answer: Yes, building an ADU raises your property tax bill, but only by the assessed value of the new unit. Your existing home keeps its Proposition 13 base value and is not reassessed. In the Bay Area, the increase is typically $1,500 to $3,000 per year, depending on the ADU's size and assessed value. Key Takeaways No full reassessment: Only the "new construction" portion (the ADU) is assessed at current market value. Your primary residence stays protected under Propos
