Development standards for accessory dwelling units. An ADU shall comply with the following standards:

A. Configuration. An ADU may be located either within, attached to, or detached from the primary structure.

B. Density. Only one ADU may be created in conjunction with each single-family residence.

C. Minimum lot size. An ADU may be established on any legally established parcel meeting applicable standards of this chapter.

D. Maximum unit size. The gross floor area, calculated from finished wall to finished wall. ADU shall not exceed 800 square feet or 50 percent of the primary single-family structure, not including garage and/or detached accessory buildings (whichever is less). ADUs created entirely within existing basements may exceed 800 square feet, provided they are not larger than the size of the remainder of the overall home.

E. Minimum unit size. The gross floor area of an ADU shall not be less than the requirements of the Washington State Building Code.

F. Setbacks and lot coverage. Additions to existing structures, or the construction of new detached structures, associated with the establishment of an ADU shall not exceed the allowable lot coverage or encroach into required setbacks as prescribed in the underlying zone. The applicable setbacks shall be the same as those prescribed for the primary structure, not those prescribed for detached accessory structures.

G. Scale and visual subordination. New detached ADUs, or ADUs extending from existing structures, shall not comprise more than 50 percent of total visible façade area of the primary structure and other outbuildings not including the ADU, as seen from the front of the lot. ADUs shall be subject to a maximum height of 25 feet.

H. Parking. No additional on-site parking is required in conjunction with the establishment of an ADU.

I. Design and appearance. ADUs that are separate or extending from existing structures shall be architecturally compatible with the principal dwelling.

J. Construction standards. The design and construction of the ADU shall conform to all applicable standards in the building, plumbing, electrical, mechanical, fire, health and any other applicable codes. (Ord. M-4377 § 2(g), 2022; Ord. M-4209 § 2, 2017; Ord. M-3959 § 38, 2010; Ord. M-3701 § 24, 2005; Ord. M-3643, 2004)