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Accessory Dwelling Unit (ADU) Permit in Centennial, Colorado

Required to establish an Attached, Detached, or Interior Accessory Dwelling Unit on a residentially-zoned lot in Centennial. Implements Colorado HB24-1152 (state ADU mandate) via Centennial Land Development Code Section 12-3-603(H). ADUs are optional for property owners (not mandatory) but the City must allow them where the LDC permits.

Verified 2026-07-03 · Source

When you need this permit

  • Allowed in zoning districts: AG, RS, RA, RU, NC, NI, and (limited to single-family lots with single-family homes) CG, AC, and UC
  • Only one ADU allowed per single-family detached dwelling; lots with an ADU cannot be subdivided so the ADU sits on a separate platted lot, and the ADU cannot be sold independently of the principal dwelling
  • Must be a permanent, habitable structure — mobile homes, recreational vehicles, and travel trailers are prohibited
  • Must receive a will-serve letter from all applicable utility districts and connect to utilities per that provider's requirements (tap fees, metering, and construction-permit requirements vary by individual water district)
  • Minimum setbacks and maximum building coverage match those of the principal structure for the zone district (LDC Section 12-3-301 for setbacks, Section 12-3-205/Table 12-3-301 for building coverage)
  • Maximum height: same as principal dwelling for attached ADUs; 17 feet for detached ADUs (LDC Section 12-3-204 for height measurement)
  • Size limit: <=50% of the principal dwelling's building footprint, OR the full existing footprint of an attic/basement conversion with no additional construction expanding that space
  • ADU must have its own separate entrance (exterior door or via a shared foyer/mud room)
  • Detached ADUs and attached-addition ADUs must match the main house in at least 3 of: roof pitch/form, soffit/fascia style, exterior wall cladding, window style/trim/orientation, exterior door style, architectural features (recessions, dormers, balconies, porches, columns, entry features), or color palette
  • One additional off-street parking space required beyond what the principal dwelling requires (may use driveway space if available)
  • Short-term rentals are NOT allowed within ADUs
  • If the property owner does not live on the property, the ADU must be registered with the City via ADU Rental Registration
  • A pre-submittal meeting (per LDC Section 12-14-303) is required before submitting the building permit application
  • A separate address assignment is required for every ADU (applied for through the Centennial Customer Service Portal)
  • Compliance with Centennial Municipal Code Chapter 18 (Building Regulations) is required, same as any building permit
  • HOAs and civic associations may impose additional or more restrictive rules on ADUs, and it is the property owner's responsibility to comply with those private covenants separately from City requirements

Required documents

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Fee schedule

Building Permit Fee — valuation-based (same schedule as new construction)City of Centennial ADU page explicitly states ADU building permit fees are based on total project valuation, referencing the same Building Permit Fee Schedule (PDF, 269KB) used for all other building permits; no separate ADU-specific fee schedule or waiver was found published by the City as of this review
$23.50 minimum ($1-$500 valuation), scaling per the Building Permit Fee Schedule table

Review timeline

Plan reviewCentennial’s published plan-review target
5–10 business days

How long did your Accessory Dwelling Unit (ADU) Permit permit actually take in Centennial?

Anonymous — one question, no email. Answers are combined and only shown once at least 5 people have reported.

Inspection process

  1. 1

    Foundation/Framing/Rough-In

    Standard building-permit inspection sequence applicable to the ADU's construction type (attached addition, detached structure, or interior conversion)

  2. 2

    Final

    Final inspection prior to Certificate of Occupancy; separate address must already be assigned

See the full Centennial inspection guide — scheduling & re-inspection fees →

Tips

  • A pre-submittal meeting is mandatory before applying for the building permit — this is a distinct extra step compared to most other residential permit types in Centennial.
  • Budget time for the separate Address Assignment process; ADUs cannot share an address with the principal dwelling.
  • Check with your water district early: metering, tap fees, and additional construction-permit requirements for ADUs vary by individual utility provider and are not standardized citywide.
  • An ADU and a new principal single-family dwelling can be built at the same time, as long as the principal dwelling's permit has commenced construction within 180 days of issuance or shows progress every 180 days.
  • Review timeline resolves to 5-10 business days depending on ADU type, every endpoint traceable to a named row in the City's published Building Permit Review Schedule (Residential Permits section, verified via plain-curl fetch HTTP 200, 2026-07-03). The Review Schedule has no literal 'ADU' row, but the City's own ADU guide PDFs classify each ADU type into a construction category that IS a named Review Schedule row: (1) the Attached ADU guide is titled 'ATTACHED ACCESSORY DWELLING UNIT (ADU) ADDITION' and states it is used 'when additional space for use as an ADU will be built adjoining the principal' dwelling — an ADDITION, which the Review Schedule places at 10 business days; (2) the Detached ADU guide is used 'when an ADU will be constructed that is entirely detached or separated from' the principal dwelling — a new ACCESSORY STRUCTURE, which the Review Schedule's 'Additions, temporary or accessory structures and swimming pool/spa' row places at 10 business days; (3) the Internal Conversion (Interior) ADU guide is used 'when converting space in an existing home for an ADU when no structural additions are required' — an ALTERATION/basement-finish conversion, which the Review Schedule's 'Alterations, basement finish, deck/pergola/patio cover, demolition, miscellaneous...' row places at 5 business days. Thus min 5 (interior conversion) to max 10 (attached addition or detached accessory structure) business days after the plan review fee is paid; the mapping is grounded in the City's own guide-title definitions, not inferred. Re-submittals/revisions are 5 business days. The mandatory pre-submittal meeting (303-754-3321) is still where staff confirm the exact classification for a given project.

Frequently asked questions

Yes. All ADUs are required to maintain a separate address from the principal dwelling, obtained through the Centennial Customer Service Portal's Address Assignment Plan process.

In Centennial, the published Building Permit Fee — valuation-based (same schedule as new construction) is: $23.50 minimum ($1-$500 valuation), scaling per the Building Permit Fee Schedule table. These are the jurisdiction's own published figures — see the fee schedule table and source citations on this page.

Centennial's published plan-review target for an accessory dwelling unit (adu) permit is 5–10 business days.

You'll need: Pre-Submittal Plan Application; Address Assignment Plan Application; Will-Serve Letter. Depending on your project, Centennial may also ask for: Attached ADU Addition Guide (PDF, 2MB); Detached ADU Guide (PDF, 1MB); Interior ADU Guide (PDF, 5MB); ADU Rental Registration. See the required-documents checklist on this page for details on each.

Centennial requires 2 inspection(s) for an accessory dwelling unit (adu) permit, in order: Foundation/Framing/Rough-In, Final. Schedule each through City of Centennial Building Division (Community Development Department) (303-754-3321).

Apply through City of Centennial Building Division (Community Development Department) at Centennial Civic Center, 13133 E. Arapahoe Rd., Centennial, CO 80112. Phone: 303-754-3321, email: buildingdivision@centennialco.gov. Office hours: Monday - Tuesday: 8 a.m. - 5 p.m.; Wednesday: 9 a.m. - 5 p.m.; Thursday - Friday: 8 a.m. - 5 p.m. Workstations are available at the Building Division office for online portal use. 24-Hour Citizen Response Center: 303-325-8000.. Official information: https://www.centennialco.gov/Government/Departments/Building.

No. Only one ADU is allowed per single-family detached dwelling. Source: City of Centennial ADU FAQ.

No. ADUs must be permanent, habitable structures; mobile homes, recreational vehicles, and travel trailers are prohibited. Source: City of Centennial ADU FAQ.

Sources & verification

Verified against official sources. Last reviewed 2026-07-03.

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 Centennial building department before you submit. PermitBase is an independent reference and is not affiliated with any government agency.

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Accessory Dwelling Unit (ADU) Permit in other cities

Broomfield, ColoradoLoveland, ColoradoHamilton, MontanaHayden, IdahoLivingston, MontanaOro Valley, ArizonaPocatello, IdahoPost Falls, Idaho

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