Arvada, CO Accessory Structures: ADU Rules (2026)

Section 5-1-5-2(A) allows an Accessory Dwelling Unit in conjunction with any single-family detached dwelling in residential, OT, and MX zoning districts, and Subsection (B) requires the ADU to meet the same development standards as the principal unit except where this Section says otherwise. Subsection (C) splits ADUs into two types for Building Code purposes: a Type A ADU is detached from the principal dwelling and treated as a separate dwelling unit, while a Type B ADU sits inside a basement, an upper story, or an attachment to the principal home, and is also treated as a separate dwelling unit even though its occupants do not live as a single household with the main home.

Subsection (D) requires one additional on-site parking space for the ADU beyond what the principal dwelling already needs, and that space may be in tandem with other required spaces; a garage built for the ADU occupants cannot exceed 250 square feet. Subsection (E) caps unit size two ways at once: an ADU cannot exceed 40 percent of the principal building's living space, and it must also fall within the lot-size-based ceiling in Table 5-1-5-2: 600 square feet on lots of 6,000 square feet or less, 850 square feet on lots from just over 6,000 up to 12,499 square feet, 1,000 square feet on lots from 12,500 square feet to one acre, and 1,200 square feet on lots larger than one acre.

Because ADUs share the same underlying zoning standards as the principal home under Subsection (B), they are also bound by the Division 5-1-5-1 rules that apply to every residential accessory structure, including setback, easement, and maximum-coverage limits that apply citywide.