Accessory Dwelling Unit (ADU) Permit in Centennial, Colorado
VerifiedRequired 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
- Required
Pre-Submittal Plan Application
Required pre-submittal meeting application via the Centennial Customer Service Portal, prior to the building permit application, per LDC Section 12-14-303
- Required
Address Assignment Plan Application
Required to obtain a separate address for the ADU, via the Centennial Customer Service Portal; requires the main home's address and applicant contact info
- Optional
Attached ADU Addition Guide (PDF, 2MB)
City of Centennial submittal guide for attached ADU additions
- Optional
Detached ADU Guide (PDF, 1MB)
City of Centennial submittal guide for detached ADUs
- Optional
Interior ADU Guide (PDF, 5MB)
City of Centennial submittal guide for interior (basement/attic) ADUs
- Required
Will-Serve Letter
Required from all applicable utility districts serving the property as part of the building permit application
- Optional
ADU Rental Registration
Required only if the property owner does not live on the property; steps and required documents detailed in the City's ADU Rental Registration handout
Fee schedule
| Fee type | Amount | Notes |
|---|---|---|
| Building Permit Fee — valuation-based (same schedule as new construction) | $23.50 minimum ($1-$500 valuation), scaling per the Building Permit Fee Schedule table | 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 |
Review timeline
5–10 business days
Centennial’s published plan-review target
Inspection process
- 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
Final
Final inspection prior to Certificate of Occupancy; separate address must already be assigned
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
- Can I build more than one ADU on my Centennial lot?
- No. Only one ADU is allowed per single-family detached dwelling. Source: City of Centennial ADU FAQ.
- Can I use an RV as an ADU in Centennial?
- No. ADUs must be permanent, habitable structures; mobile homes, recreational vehicles, and travel trailers are prohibited. Source: City of Centennial ADU FAQ.
- Do I need a separate address for my ADU?
- 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.
Sources & verification
Verified against official sources. Last reviewed 2026-07-03.
- City of Centennial Building Division (Community Development Department) — official building department
- Accessory Dwelling Units (ADUs) | City of Centennial
- HB24-1152 Accessory Dwelling Units | Colorado General Assembly
- ADU Rental Registration Contact Info Handout (PDF) | City of Centennial
- Building Permit Fee Schedule (PDF) | City of Centennial
- Building Permit Review Schedule | City of Centennial
- Building Permit Classifications | City of Centennial
- Attached ADU Addition Guide (PDF) | City of Centennial
- Detached ADU Guide (PDF) | City of Centennial
- Interior ADU Guide (PDF) | City of Centennial
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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