The City of Palo Alto permits ADUs in all residentially zoned districts.

ADU Unit Size: The maximum size of an attached accessory dwelling unit living area shall not exceed 600 square feet and shall not exceed 50% of the existing living area of the primary existing dwelling unit. The accessory dwelling unit and any covered parking provided for the accessory dwelling unit shall be included in the total floor area for the site, but the covered parking area is not included in the maximum 600 square feet for attached unit. Any basement space used as an accessory dwelling unit or portion thereof shall be counted as floor area for the purpose of calculating the maximum size of the accessory unit.