Your Guide to Building Accessory Dwelling Units (ADUs)
An accessory dwelling unit (ADU) is a self-contained residence located on the same property as a primary residence. ADUs are smaller than the main house, and have their own separate cooking, sleeping, and bathroom facilities.
ADUs can be attached to the primary home by constructing an addition or converting space in existing structures such as a garage, attic or basement, or they can be detached as a stand-alone unit.
Things to Know About Building Your ADU
Will It Fit? Your ADU will need to comply with land use regulations that may vary depending on the zoning of your property. Try this tool to check your zoning designation.
Tigard ADU Standards
- Number Allowed
Up to two ADUs are allowed per property, only one may be detached.
Detached ADUs must be 800 square feet or less. Attached ADUs must be smaller than the main house.
The maximum height of a detached ADU is 25 feet. The maximum height of an attached ADU is the same as the maximum height of the main house and varies by zone.
Setbacks are the same as the main house and vary by zone, with the exception that a detached ADU may be located within 5 feet of a rear property line if it is 15 feet or less in height.
- Lot Coverage
In the R-7 and R-12 zones, the ADU cannot cause the lot coverage to exceed 80%. Lot coverage is the total square footage of all impermeable surfaces, including buildings, paving, and roofed structures.
No additional parking is required.
- Home Businesses
Home businesses with customers coming to the home are prohibited on properties with more than one ADU.
Preparing Your Budget
Financing an ADU is often one of the most difficult steps for property owners. Most ADUs cost anywhere between $60,000 to $200,000, depending on the size, type of construction (retrofit vs. new construction), and the desired level of customization and included amenities.
There are typically two options offered by most local banks and credit unions that will work.
- Option 1 - Use existing home equity
- Option 2 - Use a construction loan based on the projected value of your home after the ADU is completed
Both options can be accomplished by either refinancing the property through a new first position mortgage or using a home equity line of credit (HELOC). Rates are typically lower on a new mortgage, but the fees are typically lower on a HELOC. In most cases, fees can be financed into the loan using both products.
Construction of an ADU can trigger an increase in property taxes. Building an ADU does not cause the reassessment of your entire property. Under state regulations, assessors can only consider the added value of the ADU. This means that the added amount of taxes is typically small compared to the overall tax bill.
To avoid surprises, take some time to prepare a complete project budget that includes potential fees. Construction of an ADU, in the City of Tigard, will require payment of fees, including:
- Land Use and Building Permit Fees
- Tigard Parks and Transportation System Development Charges (SDCs). Exemptions are available! See FAQs section.
- Washington County Transportation Development Tax
Potential Additional Fees:
- Engineering Permit Fees- if you are doing water line work or working in the right-of-way
- Clean Water Services Fees- if more than 1,000 sf of impervious area is added then stormwater facilities are required
In certain cases, building an ADU may also require you to change the size of your utilities. Adding plumbing fixtures may require you to upsize your water meter.
- Standard 3-inch sanitary sewer line cannot serve more than 3 toilets. If the ADU will increase the total number of toilets for the primary unit and ADU combined, you will need to determine if the existing sanitary sewer line is sufficient.
- Water Meter Worksheets are available here.
Permitting and Process
What is the Process for Permitting an ADU in Tigard? There are five basic steps to getting your ADU permitted by the City of Tigard. These steps must be followed in order.
- Get land use approval: this step requires the submission of a land use application, a narrative and site map demonstrating compliance with the standards, and a fee.
- Get an additional address: Application available here.
- Obtain exemptions: If seeking an exemption from SDCs, submit an exemption application and a recorded deed restriction to the Finance department. There is no application fee.
- Submit for engineering permits: if applicable, for work in the public right-of-way.
- Submit for building permits: these permits include building, plumbing, electrical, and mechanical permits. Fees vary.
» Building permit applications available here.
» Tigard building code considerations for ADUs available here.
Frequently Asked Questions
Are there incentives for building an ADU?
Tigard SDCs and a construction excise tax are exempt for ADUs.This represents a savings of approximately $11,000 for property owners who are approved for an exemption.
What about my HOA?
If you live in a neighborhood with a homeowners association (HOA), be sure to check the code, covenants and restrictions (CC&Rs) for your neighborhood to identify any rules that affect ADUs. Some CC&Rs prohibit ADUs or impose additional restrictions. City staff are not able to review or enforce CC&Rs, so it’s best to do your own research and obtain any necessary HOA approvals before starting the land use and permitting process. If you find that your community’s CC&Rs restrict ADUs, consider working with your neighbors and the HOA to amend the CC&Rs to remove obstacles to ADUs.
Are tiny homes ADUs and vice versa?
Under the Oregon state building code, a tiny home is any house that is under 400 square feet. Tiny homes on wheels are considered recreational vehicles. In Tigard, it is not legal to live in a recreational vehicle in most residential zones. However, if placed on a permanent foundation, a tiny home can be considered an ADU. So, while some tiny homes can be used as an ADU, not all ADUs are tiny homes.
Can I rent my ADU?
Yes. Renting out an ADU can offer steady income and provide a new opportunity for someone to live in your neighborhood. If you’re planning to rent out the ADU or the primary unit, it’s worth thinking through the practical implications of becoming a landlord. The Oregon State Bar Association provides a helpful guide to the laws governing landlord-tenant law at www.osbar.org/public/legalinfo/landlordtenant.html
Can I rent my ADU out as a short-term rental on AirBnB or VRBO?
The City of Tigard does not allow short-term rentals (AirBnB, VRBO, etc.) in residential zones, although some commercial and mixed-use zones do allow for short-term rentals. This means that most ADUs cannot be used as a short-term rentals.