Boulder, CO Accessory Structures: ADU Impact Fees (2026)

Boulder charges a capital facility impact fee on new floor area and land use intensification citywide, split among classifications for parks and recreation, human services, affordable housing, municipal facilities, and police and fire, under Chapter 8-9. Section 8-9-3(c) lists several carve-outs from that fee. Paragraph (c)(4) exempts a residential accessory building or an addition of 200 square feet or less from the parks, human services, municipal facilities, police, fire, and transportation impact fees (usable once per dwelling unit existing as of January 1, 2010), and separately exempts an addition of 500 square feet or less from the affordable housing impact fee alone (usable once per dwelling unit existing as of January 31, 2026).

Paragraph (c)(5) exempts any single-unit dwelling of 2,000 square feet or less from the affordable housing impact fee entirely. Paragraph (c)(6) then carves out accessory dwelling units specifically: any floor area in a single-unit dwelling use that is part of an ADU built to the specific use standards of section 9-6-3 is exempt from the affordable housing impact fee, regardless of the size threshold that applies to additions generally. The fee itself is otherwise due at building permit issuance for most development and just before final inspection for new buildings, calculated under the schedule in section 4-20-62, and the city credits each property for what the existing use would have already paid.

A fee payer who disputes how the city manager classified their use can request a Chapter 1-3 quasi-judicial hearing before a different hearing officer than the one who made the original call.