Accessory Dwelling Unit (ADU) Permit in Boulder, Colorado
Required for construction of a new attached or detached ADU on a residential property in the City of Boulder. ADUs are permitted by-right in most residential zoning districts (except RH-6, MH, BMS, BCS, IS-1, and IM). As of September 1, 2023, ADUs are reviewed and approved through the standard building permit process without a prior administrative review step, and off-street parking and owner-occupancy requirements were removed for all ADUs.
Verified 2026-06-30 · Source
When you need this permit
- Permitted by-right on lots with detached dwelling units in most zoning districts — verify via the city's interactive zoning map
- Detached ADU: maximum 800 sq ft (standard); up to 1,000 sq ft for an affordable ADU (75% AMI) or on a historic property
- Attached ADU: maximum 1/2 of the principal structure's floor area or 1,000 sq ft, whichever is less (standard); up to 2/3 of principal floor area or 1,200 sq ft, whichever is less, for an affordable ADU/historic property
- Height: detached ADU 20 ft standard, up to 25 ft with an 8:12 or steeper roof pitch; attached ADU up to 35 ft (same as principal structure)
- As of Sept. 1, 2023, off-street parking and owner-occupancy requirements were removed for all ADUs
- Short-term rental (under 30 days) of an ADU is prohibited unless the short-term rental use was established before February 1, 2019
- Long-term rental of the ADU and/or principal unit is permitted; a rental license is required to rent
- An ADU may not be sold or conveyed separately from the principal dwelling unit
- Homeowner self-permitting does NOT apply to detached ADUs — a licensed contractor is required for detached ADU construction (the primary-residence homeowner exception is limited to the owner's single-family detached home and its accessory structures other than a detached ADU)
Required documents
- Req
Accessory Dwelling Unit (ADU) Application
Building permit application with ADU-specific supplemental documentation
- Opt
Accessory Dwelling Unit (ADU) Guide
City of Boulder's current ADU zoning, size, height, and process guidance document
- Req
Site Plan
Zone lot lines, existing structures, proposed ADU location, setbacks
- Opt
Declaration of Use (for Affordable ADU)
Required for ADUs seeking the increased affordable-ADU size allowance
Fee schedule
| Fee type | Amount | Notes |
|---|---|---|
| Building Permit Fee — valuation-based (same table as new construction) | Varies by valuation — see Residential Building Permit fee tiers (City of Boulder Valuation Table, R-3 ADU use category) | 2026 Schedule of Fees — ADU is explicitly listed under the R-3 Residential building-use category on the City of Boulder Valuation Table (e.g., $170.80–$182.23/sf for Type V-B construction) |
| Plan Check Fee | 25% of the Building Permit Fee (single-family residential, initial application) or per applicable Compatible Development rate | 2026 Schedule of Fees, Plan Check Fee |
| Energy Code Fee — Residential | $83.90 | 2026 Schedule of Fees, Energy Code Fee |
Review timeline
~1–1 business days
Typical estimate — confirm current times with the Boulder building department
Inspection process
- 1
Foundation
Footings and foundation before concrete pour
- 2
Framing
Structural framing, egress, fire separation (if attached)
- 3
MEP Rough-In
Mechanical, electrical, plumbing rough-ins before walls closed
- 4
Final
All work complete; Certificate of Occupancy required before occupancy
Tips
- Since Sept. 1, 2023, Boulder ADUs go straight through the standard building permit process — no separate administrative zoning review is required first, and owner-occupancy/parking requirements were dropped citywide.
- A detached ADU CANNOT be built under the homeowner self-permit exception, even if you own and occupy the primary home — a licensed contractor is required for the ADU itself.
- If you plan to rent the ADU or the principal unit, a separate rental license is required, and (for the principal unit or any licensed rental on the property) SmartRegs energy compliance applies as a condition of that rental license.
- Short-term rental of an ADU is prohibited unless that specific short-term rental use predates February 1, 2019.
Frequently asked questions
- Can I build my own ADU as a homeowner in Boulder?
- No — the homeowner self-permit exception in Boulder applies only to a single-family detached home and its accessory structures other than a detached ADU. Detached ADU construction requires a licensed City of Boulder contractor.
- Do I need off-street parking for an ADU in Boulder?
- No. As of September 1, 2023, the City of Boulder removed the off-street parking requirement (along with the owner-occupancy requirement) for all ADUs.
Sources & verification
Verified against official sources. Last reviewed 2026-06-30.
- City of Boulder Planning & Development Services — official building department
- Accessory Dwelling Unit (ADU) Guide — City of Boulder
- Accessory Dwelling Units — City of Boulder
- Accessory Dwelling Unit (ADU) Application — City of Boulder
- Planning and Development Services 2026 Schedule of Fees — City of Boulder
Fees, timelines, and adopted codes are researched from each jurisdiction's published records — see how we verify. Requirements change and vary by project, so always confirm the current details with the Boulder building department before you submit. PermitBase is an independent reference and is not affiliated with any government agency.
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