Yes, a building permit is required for all proposed dwelling unit types.
Fire-Resistive Construction. Pursuant to Section R302of the CA Residential Code as amended by the City of Sonoma, Dwelling units in two-family dwellings shall be separated from each other by wall and floor assemblies having not less than a 1-hour fire-resistance rating where tested in accordance with ASTM E119 or UL 263. Fire-resistance-rated floor/ceiling and wall assemblies shall extend to and be tight against the exterior wall, and wall assemblies shall extend from the foundation to the underside of the roof sheathing.
Automatic Fire Sprinkler Systems. Pursuant to CA Govt. Code Section 65852.2(c) & (e) [Effective 1/1/17], CA State Fire Marshal Information Bulletin 17-001 and Chapter 14.10.045 of the Sonoma Municipal Code, an automatic fire sprinkler system is required for:
New detached accessory dwelling units when: The primary dwelling on the property has or will have as a result of the current project, an automatic fire sprinkler system installed; OR the detached accessory dwelling unit floor area exceeds 1,200 sq. ft.
New attached accessory dwelling units constructed within or added to an existing primary residence when: The existing primary dwelling on the property already has an automatic fire sprinkler system installed; OR the addition to or alteration of the existing primary dwelling to facilitate the creation of an attached accessory dwelling unit (including the subject ADU project), plus any other building permits issued for the building within any 36 month period, exceeds a total permit valuation of $100,000.
For more information about building permit requirements, visit the Building Department page.