Single-Family & Detached ADU Tax Exemption

Exemption for Physical Improvement to a Single Family Dwelling

New in 2020

The construction of a detached accessory dwelling unit (ADU) is now available for tax exemption.

Any physical improvement to single-family dwellings upon real property, including constructing an accessory dwelling unit, whether attached to or within the single-family dwelling or as a detached unit on the same real property, shall be exempt from taxation for the three assessment years subsequent to the completion of the improvement to the extent that the improvement represents thirty percent or less of the value of the original structure. SEE 6231-S2.SL for more details.

Q: What is an accessory dwelling unit?

A: Accessory Dwelling Unit (ADU): A separate additional living unit, including separate kitchen, sleeping, and bathroom facilities, attached or detached from the primary residential unit, on a single-family lot. ADUs are known variously as: "Mother-in-law apartments," "Accessory apartments," or "Second units."

Step 1
Complete and file your tax exemption application – details below.

Step 2
Contact our Developer Services Center to find out what additions, improvements, or ADU you can make or add to your home along with what permits are needed.

Development Services Center

Step 3
Get your permits and get to work on your renovations.

Step 3
Enjoy your new space and a partial tax exemption!

Program Benefits

When you decide to make home improvements through remodeling and additions, there is a three-year property exemption program available. According to RCW 84.36.400, physical improvements to a single family dwelling upon real property are exempt from property tax for three assessment years after the improvements are completed to the extent that the improvement represents 30% or less of the value of the original structure.

Qualifying Definitions

Single family dwelling means a detached dwelling unit and the lot on which the dwelling stands which is designed for, and not occupied by, more than one family.

Physical improvement means any addition, remodeling, renovation, structural correction or repairs which materially adds to the value or condition of an existing dwelling, including the addition of, or repairs to, garages, carports and patios attached to and compatible with the dwelling. Improvements for tax exemption purposes do not include swimming pools, golf greens, fences, outbuildings, or general maintenance.

Application Process

The homeowner must file a claim for the exemption with the Assessor before the improvements are completed. (NOTE: The homeowner may not claim this exemption more than once in a five-year period on the same dwelling.)

When the improvements are completed, the homeowner must submit a written notice of completion to the Assessor.

Application Form

Mail completed form to:
Spokane County Assessor
1116 W Broadway Avenue
County Courthouse, 1st Floor
Spokane, WA 99260-0010

For questions or to submit via email:

Example of Calculation

The following example should be used only as a general guide and cannot be relied upon for any other purpose.

In 2019, a homeowner completed the addition of a family room and the renovation of the kitchen. These improvements cost the homeowner $60,000.

Assessor determines true & fair value of dwelling prior to improvements: $150,000
Assessor determines true & fair value of improved dwelling: $200,000
Difference (value of physical improvements): $50,000
30% of the unimproved dwelling ($150,000 x 30% = $45,000)
Amount of Exemption: The lesser of the following two numbers:
- Difference between the value of the improved & unimproved dwelling ($50,000)
- 30% of the unimproved dwelling ($45,000)

The assessed value of the improved dwelling will be reduced by $45,000 for the next three assessment years (2020, 2021, and 2022).

Contact Information

Contact Teri Stripes,
Economic Development Specialist at: