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Accessory Dwelling Units (ADU)
An Accessory Dwelling Unit (ADU), sometimes called an "in-law apartment" or "carriage house," is typically an additional housing unit within, or on the same lot as, a single-family home with entries and amenities that are separate from the primary residence. Please review the information below to see what's required for different types of ADUs before submitting your application.
Getting Started
Review the list of required documents and steps below before beginning the application process. Once you are ready to apply, you will login to our permitting system, Arvada Permits, enter the required information and upload PDF plans and related documents to your application. Utilize the eTRAKIT Online Application.
Types of Accessory Dwelling Units
The City of Arvada has two categories for Accessory Dwelling Units (ADU):
Type A
An Accessory Dwelling Unit that is detached from the principal dwelling. It is considered lockable and rentable.
Type B
An Accessory Dwelling Unit with the following characteristics:
- Located inside a single-family dwelling, or
- Attached to a single-family dwelling
- Whose occupants and the occupants of the principal dwelling do not live together as a single household unit and which is rented.
- Typically have a separate access from the principal dwelling that is locked off from the principal dwelling.
Both Type A and B Accessory Dwelling Units are considered a separate dwelling unit from the principal dwelling under the building code. Fire separation from the primary dwelling and a separate HVAC system are required. Water and sanitary sewer service for ADUs must be connected to the service lines of the primary dwelling unit and may not have separate services.
If your home is part of a Homeowner's Association (HOA) you must gain approval from the HOA in addition to permits and approvals from the City of Arvada. An approval and permit issued by the City of Arvada does not overrule HOA approval.
ADU permits are only issued to Licensed Contractors with a type 1B, 2B or 3B license. To ensure your permit is issued in a timely manner, please make sure to submit the correct documentation for all subcontractors. Permits without sub-contractors listed will be placed into a hold and will not be allowed to start construction. Please review contractor qualifications prior to submitting your application.
The City of Arvada allows ADUs in all residential zone districts provided that an existing detached single-family home exists on the lot. Each zone district has different development standards such as the maximum lot coverage you are allowed, and where structures can be located on individual lots.
Please use our Maps and Property Search to find your zone district. Once you launch the interactive map search, search for your property and click on it to find a link to the development standards for your zoning district.
The maximum ADU size is correlated to the size of your existing single-family residence and lot size. For all Type A and Type B ADUs that are newly constructed additions to the existing home, the ADU cannot be larger than 40% of the living space of the primary home. Garages, unfinished basements, and patios are not considered living space.
In addition, an ADU cannot be larger than the maximum floor area listed below that is correlated to the lot size:
| Lot Size | Maximum Floor Area |
|---|---|
6,000 square feet or less | 600 square feet |
Greater than 6,000 square feet and up to 12,499 square feet | 850 square feet |
12,500 square feet and up to 1 acre | 1,000 square feet |
Greater than 1 acre | 1,200 square feet |
On corner lots, Type A ADUs shall be set back at least ten feet behind the façade of the main home along both street frontages.
Type B ADUs that are constructed within the footprint of the existing home (such as in the basement) are exempt from the maximum size restrictions listed above and are instead limited to a maximum size of 50% of the floor area of the principal dwelling. For example, if a home has a 1,000 square foot basement, an ADU could be established in the basement if the rest of the principal dwelling is at least 1,000 square feet.
Additional zoning requirements related to architectural compatibility, parking, landscaping, and a required deed restriction are available in Chapter 5 of the Land Development Code.
The City of Arvada is committed to providing plan reviews within our timelines, however, workload of the current development environment in the City of Arvada can affect these timelines. Complete submittals will help with keeping within this timeframe. If your application package is incomplete your project may not be accepted and can cause delays in approving your application.
Review Timeline for ADU Permits
| Type | Review Time Required |
|---|---|
| A | 3 Weeks |
| B | 1 to 2 Weeks |
Required Submittal Documents
Permit applications that are submitted with complete information will be reviewed. If you have questions about items that are required please email Building Permits Division.
Please provide each plan set individually in separate PDFs. Foundation and structural plans must be stamped by a professional licensed in the State of Colorado (engineer or architect)
Plans must include pertinent design information that includes wind speed design, snow load, and frost depth.
Plans included in package:
- Architectural plans, Elevations, Cross Sections, and Electrical.
- Plot Plan detailing: size, setbacks, lot coverage, landscaping, and parking.
- Grading Plan
- Utility Plan
- Gas line calculations
- Structural plans, stamped and signed by an engineer
- Foundation Plans, stamped and signed by an engineer
- Truss specification package, stamped and signed by an engineer
- Soils report, stamped and signed by an engineer
- Manual J, D, and S calculations
- RESCheck or HERS Rating calculations, if performance energy path is utilized
- Declaration of Covenants (obtain from Planning)
| Type | Review Time Required |
|---|---|
| A | 3 Weeks |
| B | 1 to 2 Weeks |
ADUs within the existing footprint of primary residence:
- Plot Plan detailing size, setbacks, lot coverage, landscaping, and parking
- Architectural Plans (floor plans)
- Approved 1 Hour Fire Separation Detail with STC Rating (Sound Transmission Class, 45 or greater)
- Gas line calculations*
- RESCheck or HERS Rating calculations, if performance energy path is utilized*
- Declaration of Covenants (obtain from Planning)
ADUs expanding the existing footprint of primary residence (Addition):
- Plot Plan detailing size, setbacks, lot coverage, landscaping, and parking
- Architectural Plans (floor plans), Elevations, Cross Sections, and Electrical
- Approved 1 Hour Fire Separation Detail with STC Rating (Sound Transmission Class, 45 or greater)
- Grading Plan
- Foundation and Structural Plans, stamped and signed by an engineer
- Truss Specifications, stamped and signed by an engineer
- Soils Report, stamped and signed by an engineer
- Gas line calculations*
- Manual J, D, and S Calculations*
- RESCheck or HERS Rating calculations, if performance energy path is utilized*
- Declaration of Covenants (obtain from Planning)
*These items may be requested depending on the project.
Fees
Fees are charged based on the complete contract value or on the square footage, whichever valuation is greater. A permit for an ADU will include a Building Permit Fee, Use Tax Plan review fee, and recording fees. Depending on the project you may also have fees for Plumbing, Mechanical, and Electrical. You can get an estimate on your fees by clicking on the "Fee Calculator" button below. Please be aware that additional fees may apply and will be identified through the permitting process.
Use the Fee Calculator.
Permit Issuance & Inspections
Once the ADU permit application has been reviewed and approved by Building, Planning, and Engineering, the permit will be ready to be issued. The applicant on the permit will be notified via email when the permit is ready for payment. All fees must be paid and the applicant must download the proper permit documents to have available on site. Fees can be paid online using a credit card. If another type of payment is requested, please visit the Building Counter to make a payment.
Please note that after permit issuance, the primary residence and ADU will be re-addressed as Unit A and Unit B respectively.
ADUs must be connected to the utilities of the principal dwelling unit and may not have separate services. Upon completion of your ADU, you may be assessed the Metro Wastewater District Fee. This fee must be paid before a CO will be issued.
All projects are required to have the following City of Arvada approved documents on site. All approved plans can be downloaded on eTRAKIT and can be made available either in a physical paper copy or as an electronic copy, unless noted otherwise.
- Approved Plans (Electronic or physical)
- Permit (Physical copy)
Depending on the scope of your project, various inspections are required throughout the duration of construction. Third party inspection companies typically perform all foundation inspections and special inspections required per the approved plans. Proof of inspection is required to be submitted. All third party inspections can be attached to the permit via arvadapermits.org. City building department staff will perform the remaining structural, mechanical, plumbing, electrical, and building inspections. For more information about scheduling and review information visit the Scheduling Inspections page.
A Certificate of Occupancy (CO) will be required to be issued to finalize this permit. Please provide 3 business day notice to the Building Counter to ensure that all departments have sufficient time to review your request.
For a Certificate of Occupancy to be requested:
- All final inspections are completed. Final Building, Electrical, Mechanical, and Plumbing. CO-Public Improvement, and Planning.
- Provide a final Improvement Location Certificate (ILC). (Type A and B if unit is an addition)
- Grading Certification. (all Type A and B if the unit is an addition)
- Provide an air leakage report (blower door report) (All Type A and B if unit is an addition)
- Energy Certification (where following a performance-based energy path) (All Type A and B if unit is an addition)
- Insulation Certificate (where following a prescriptive energy bath) (All Type A and B if unit is an addition)
- Documentation for fire protection of floor assemblies (where required)
- Foundation Inspection Form (FIF Form) (All Type A and B if unit is an addition)
- Declaration of Covenants (obtain from Planning)
Please call the Building Counter for final CO/TCO Inspection once all of the correct documentation previously mentioned has been submitted.
A Certificate of Occupancy will be issued when:
- The following departments have approved their review of the CO/TCO request:
- Engineering
- Planning
- Building
- Once request is approved by all departments, a Certificate of Occupancy will be attached to the permit and applicant will be notified via email.
If you have questions about the closing of this permit type please contact the Building Division at 720-898-7620.