Piedmont has produced a document: “Frequently asked Questions about ADUs”


  • Unit Size: An attached ADU may not exceed 50% of the existing living area up to a maximum of 800 sq. ft., subject to the zoning regulations (including floor area ratio). A detached ADU may not exceed 800 sq. ft., subject to the zoning regulations (including floor area ratio). However, under either circumstance an exception to unit size may be sought.
  • Access: The ADU must have independent, exterior access.
  • Owner Occupancy: Except for an exempt ADU, the property owner must occupy either the primary unit or the accessory unit if both are occupied and used as independent dwelling units. This restriction is recorded with the deed for the property
  • Limit of one ADU per parcel: There may be no more than one ADU on a parcel

If your proposed ADU requires one or more variances from setback, lot coverage, floor area ratio or building height regulations, you must seek a variance from the regulation(s) as part of the application you submit for design review permit. The application for variance and design review permit will be considered by the Planning Commission during a public hearing. Additional fees for the review of one or more variance request will be applied.

Can I build an accessory dwelling unit that is larger than 800 square feet?

A unit size exception of up to 1,000 sq. ft. is allowed if you agree to rent-restrict your ADU at a rent that is affordable to a low-income household. The unit size exception is increased to 1,200 sq. ft. if you agree to rent-restrict your ADU to a very low-income household. Under no circumstances is a unit larger than 1,200 sq. ft. permitted. (See Section 17.38.070.C.) ADU permit applications that seek an exception to the unit size limit are considered at a public hearing by the Planning Commission.


City of Piedmont

Piedmont Public Works