Thurston County Unincorporated
City Zoning Code

Accessory uses are permitted in any zoning district, accept as prohibited or limited in this chapter.

(Ord. 11398 § 3 (part), 1997: Ord. 6708 § 3 (part), 1980)

(Ord. No. 14182, § 3, 12-29-2008; Ord. No. 16575, § 2(Att. A.XXXIII), 12-16-2025)

The purpose of the rural accessory dwelling unit regulations is to increase options for rural housing to allow for more affordable and diverse housing choices. Accessory dwelling units (ADU) permitted under the provisions of this title apply in all Title 20 zoning districts that allow for residential uses, except R 5-12/1, R 8-24/1, and AC zoning districts or residential zoning districts within the UGAs of Yelm, Rainier, or Tenino (see Section 20.34.030 for urban ADU provisions).

1.

Within the rural unincorporated County, one ADU shall be permitted per residential parcel in conjunction with any detached single-family dwelling structure. An ADU shall not be placed on parcels with any other accessory residential structures.

2.

Density.

a.

An attached ADU, as defined under this title, does not count as a dwelling unit for the purpose of calculating density. No additional land area is required for such ADUs beyond the minimum parcel size that is required for the associated single-family dwelling structure under the applicable zoning district.

b.

An ADU conversion, as defined under this title, does not count as a dwelling unit for the purpose of calculating density. No additional land area is required for such ADUs beyond the minimum parcel size that is required for the associated single-family dwelling structure under the applicable zoning district.

c.

A detached ADU, as defined under this title, does not counts as a dwelling unit for the purpose of calculating density. No additional land area is required for such ADUs beyond the minimum parcel size that is required for the associated single-family dwelling structure under the applicable zoning district. Detached accessory dwelling units (DADUs) may only be permitted consistent with historical rural density patterns, as calculated by the department.

3.

Accessory dwelling units shall conform to the design standards in the subject zoning district.

4.

Size Limitations.

a.

Attached: The floor area of an ADU may not exceed fifty percent of the gross floor area of the principle residential structure.

b.

Conversion: There is no limit on size for the conversion of existing internal or detached space to an ADU, so long as the conversion remains within the footprint of the structure.

c.

Detached: The floor area of a new detached accessory dwelling unit may not exceed the maximum of one thousand square feet.

i.

Exception: If one transferable development right is purchased from the Long-Term Agriculture District under Chapter 20.62, the detached accessory dwelling unit is permitted a maximum floor area of one thousand two hundred square feet.

5.

Specific Standards.

a.

Attached: The addition shall visually match in type, size, trim, and materials of the existing principle structure.

b.

Conversion: Displaced parking must be replaced and additional parking must be provided subject to Chapter 20.44.030, Off-street parking, required spaces. Modifications or expansions of the converted structure shall be subject to the design standards in the subject zoning district.

c.

Detached: Detached ADU's must be built within one hundred feet of the primary dwelling unit to limit the development footprint of such units. The Director may approve an increase to this distance requirement if there are limiting factors on the property that prevent it from being within one hundred ft of the primary dwelling unit, such as the location of well, septic, or drain field, or critical areas. Increases to the distance shall be subject to a Type I review process. (Chapter 20.60 TCC)

6.

Water and Sanitation.

a.

Accessory dwelling units must have water and sanitation. For any ADU connecting to a Group A or Group B water system, a certificate of water availability (COWA) is required and shall also comply with Section 14.48.100(B)10—12. This provision applies to all ADUs, including those that may not require a building permit (e.g., internal conversions).

7.

Building Types.

a.

Accessory dwelling unit shall be any residential building type permitted in Title 14, Buildings and Construction.

8.

Access.

a.

Accessory dwelling units shall share a driveway to the public right-of-way. The maximum coverage for hard surfaces applies.

9.

[Reserved.]

10.

All accessory dwelling units shall conform with Title 14 and all other applicable codes and ordinances.

(Ord. No. 15952, § 1(Att. A, § VI), 12-15-2020; Ord. No. 16575, § 2(Att. A.XXXIII), 12-16-2025)

Editor's note— Ord. No. 15952, § 1(Att. A, § VI), adopted Dec. 15, 2020, enacted a new § 20.34.020 and renumbered the former § 20.34.020 as § 20.34.030, as set out herein. Historical notation has been retained for reference purposes.

Editor's note— Ord. No. 16575, § 2(Att. A.XXXIII), adopted Dec. 16, 2025, renumbered the former § 20.34.030 as § 20.34.050. The historical notation has been retained with the amended provisions for reference purposes.

The purpose of the urban accessory dwelling unit regulations is to increase options for urban housing to allow for more affordable and diverse housing choices. Accessory dwelling units (ADU) permitted under the provisions of this title apply to R 5-12/1, R 8-24/1, and AC districts (Grand Mound UGA), or any residential zoning districts within the urban growth areas of Rainier, Tenino, and Yelm.

1.

Two ADUs shall be permitted per residential parcel in conjunction with any permitted principle residential structure. Any combination of attached or detached ADUs is permitted.

2.

Density.

a.

An ADU, as defined under this title, does not count as a dwelling unit for the purpose of calculating density. No additional land area is required for such ADUs beyond the minimum parcel size that is required for the associated permitted principle residential structure under the applicable zoning district.

3.

Accessory dwelling units shall conform to the design standards in the subject zoning district.

4.

Size Limitations.

a.

The floor area of an ADU may not exceed the maximum of one thousand square feet.

5.

Water and Sanitation.

a.

Accessory dwelling units must have water and sanitation. For any ADU connecting to a Group A or Group B water system, a certificate of water availability (COWA) is required and shall also comply with Section 14.48.100(B)10—12. This provision applies to all ADUs, including those that may not require a building permit (e.g., internal conversions).

6.

Building Types.

a.

Accessory dwelling unit shall be any residential building type permitted in Title 14, Buildings and Construction.

7.

Access.

a.

Accessory dwelling units may share or have a secondary driveway to the public right-of-way. The maximum coverage for hard surfaces applies.

8.

All accessory dwelling units shall conform with Title 14 and all other applicable codes and ordinances.

(Ord. No. 16575, § 2(Att. A.XXXIII), 12-16-2025)

1.

Location of Accessory Uses. Accessory uses shall be on the same lot of record as the principal use or building, unless a provision of this title allows otherwise.

2.

Antenna structures and satellite dishes shall not be located within twenty feet of any property line. This requirement does not apply to satellite dishes eighteen inches or less in diameter.

3.

Buildings shall not be located in required front or side yards.

4.

Corner lot structures and planting shall comply with Section 20.07.070 (Use limitations on corner lots).

5.

Barbed wire fences are prohibited in the RL 2/1, R 5-12/1, and R 8-24/1 districts, except as accessory uses to agricultural operations of one acre or more. On industrial and commercial uses, the strands shall be restricted to the uppermost portion of the fence and shall not extend lower than a height of six feet from the nearest ground level.

6.

Each accessory dwelling unit will require one parking space, which is in addition to any off-street spaces required for the primary dwelling unit.

7.

Guest House or Rooms for Guests. Guest houses or rooms for guests are permitted as an accessory use in all residential districts as follows:

a.

The floor area shall be limited to eight hundred square feet, or fifty percent of the primary dwelling unit whichever is less; and

b.

The guest house must also be clearly subordinate and incidental to the primary dwelling unit; and

c.

Be intended to be used for the occasional housing of guests; and

d.

Cannot be rented or leased for direct or indirect compensation; and

e.

It shall be demonstrated that the sewage treatment system is properly sized to accommodate increased flow based on the number of bedrooms, or rooms that could be used for sleeping quarters; and

f.

A covenant shall be recorded on the property showing the area used for the guest house, and the conditions of approval for the guest house; and

g.

An existing structure being converted to a guest house shall meet the requirements for a guest house as specified in this code.

8.

Parking or storage of small cargo trailers and major recreational equipment in residential and rural districts, including but not limited to boats, boat trailers, camping trailers, travel trailers, motorized dwellings, recreational vehicles, tent trailers, houseboats, and horse vans are subject to the following limitations:

a.

Such equipment shall not be used for living, sleeping, or other occupancy associated with residential uses when parked, or stored on a residential lot, or in any other location not approved for such use. These types of equipment are intended for recreational use only and do not meet building, fire and safety, and health code standards associated with residential uses. Temporary occupancy is permitted but shall not exceed thirty days in any six-month period. Two thirty-day temporary occupancies within any twelve-month period must be separated by a minimum of at least forty-five days.

b.

Such equipment over six feet in average height, when not parked in a garage, carport or other structure, shall not be located in any required front or side yard reserved for building setback (except driveways).

c.

Such equipment shall not be hooked up to utilities, sewage or septic, or water facilities unless located in a recreational vehicle park. An exception can be made for an electrical extension to prevent freezing, etc. when the recreational vehicle is being stored.

d.

Such equipment shall not be attached to other structures such as, but not limited to, decks, porches, roofs, room additions, foundations, carports, storage units, accessory structures, walls or fences, dwellings, or other buildings.

e.

Travel trailers, motorized dwellings, and recreational vehicles may be temporarily occupied for six months only when located in a recreational vehicle park and hooked up to utilities, sewage or septic, and water facilities.

9.

Storage.

a.

General Provision. Outside storage shall be maintained in an orderly manner and shall create no fire, safety, health or sanitary hazard.

b.

Residential Districts. Outside storage incidental to permitted uses is allowed in all residential districts listed in this title subject to the following:

i.

Required front yard shall not be used for storage (except firewood).

ii.

Storage containers are permitted in residential districts on a temporary basis provided they are not inhabited. They shall not exceed thirty days in any six-month period or two thirty-day occupancies within any twelve-month period. They must only be used for personal use and directly related to an approved building permit or clearing and grading permit for the site.

iii.

Any storage container placed on the property longer is considered permanent and is treated as a structure subject to building permit requirements.

iv.

Junk vehicles.

(A)

A maximum of two junk vehicles or parts vehicles may be stored on a lot, or contiguous lots in a single ownership, in the RL 2/1, R 5-12/1, R 8-24/1 districts and on lots of one-half acre (21,780 square feet) or less in the R 1/20, R 1/10, UR 1/5, RR 1/5, RRR 1/5, RL 1/2, RL 1/1, LTF, LTA and MGSA districts.

(B)

A maximum of four junk vehicles or parts vehicles may be stored on lots larger than one-half acre (21,780 square feet), or on contiguous lots in a single ownership totaling more than one-half acre, in the R 1/20, R 1/10, UR 1/5, RR 1/5, RRR 1/5, RL 1/2, RL 1/1, LTF, LTA and MGSA districts.

(C)

Junk vehicles and parts vehicles shall be contained in an enclosed structure or screened. Screening must be at least six feet in height and composed of material that completely blocks the view of the junk/parts vehicle(s) from the right-of-way and abutting residential properties. Screening may consist of fences, walls, vegetation, berms or other visual barriers in keeping with the residential character of the area, as determined by the approval authority.

Vegetative screens shall achieve one hundred percent opacity, year around, within one year of planting. All vegetative screens in compliance with this section shall be maintained in a healthy condition. Any vegetation in such screens that dies shall be replaced within six months.

(D)

Required screening shall not be placed in public right-of-way.

(E)

Junk/parts vehicles may not be stored on public right-of-way.

(F)

All junk vehicles in the R 1/20, R 1/10, UR 1/5, RR 1/5, RRR 1/5, RL 1/2, and RL 1/1 districts made nonconforming by this title shall be removed from the site by March 1, 2002. All junk vehicles in the LTF, LTA and MGSA districts made nonconforming by this title shall be removed from the site by January 1, 2012.

iii.

Uninstalled mobile/manufactured homes or buildings moved from other sites may only be stored on a property while building and development permits are being processed and issued for that structure's installation on that particular property. No other form of uninstalled mobile/manufactured home storage will be permitted.

c.

Commercial and Industrial Uses. The intent of this section is to control the outdoor storage of materials and products used in production, for sale on premises, awaiting shipment or production waste in such a fashion as to insure public safety, health, welfare and to minimize detrimental visual impact upon neighboring property and/or public thoroughfares.

i.

Permitted Items. Every reasonable effort shall be made by persons operating a business to store all such materials within an enclosed building, with the following exceptions:

(A)

Where such inside storage is not practical and desirable for reasons related to health, fire or safety codes;

(B)

Where the outside storage of merchandise, manufactured products or raw materials is normal and standard practice, such as in the sale of automotive equipment, mobile/manufactured homes, lumber, gardening materials, nursery stock and the like, or on the site of construction projects;

(C)

When materials or products are temporarily stored outside incidental to shipping, delivery, loading or unloading thereof.

ii.

Storage Height and Screening. Materials and products may be stored to height maximums permitted in the particular district, subject to the provisions of performance standards/view protection in this chapter, but shall be effectively screened from view by using a solid screen six feet high. Screening may include fences, walls, vegetation, berms with vegetation, combinations of these, or other methods, all of which must provide a permanent solid screen barrier to visibility from rights-of-way and adjacent and nearby properties. Vegetation used for screening must be of sizes, types, numbers and siting adequate to achieve one hundred percent opacity within three years. All vegetation used for screening shall be maintained in a healthy condition. Vegetation used for screening that dies shall be replaced within six months. Fences and walls over six feet high require a building permit. Screening shall not be placed in the public right-of-way or in the vision clearance triangle of intersections and curb cuts.

iii.

Vehicle Storage. Outdoor storage of automobiles, trucks, farm, construction and rental equipment, trailers, boats, campers, recreation vehicles, mobile/manufactured homes and other vehicles for sale, rent or shipment (not including parking lots for residential or commercial use) shall be effectively screened from view, in residential areas and rural districts. Screening shall be of a material or vegetation sufficient to provide a solid barrier to view and shall be at least eight feet high. Screening may include fences, walls, vegetation, berms with vegetation, combinations of these, or other methods, all of which must provide a permanent solid screen barrier to prohibit visibility from rights-of-way and adjacent and nearby properties. Screening shall not detract from the residential character of the area. Vegetation used for screening must be of sizes, types, numbers and siting adequate to achieve one hundred percent opacity within three years. All vegetation used for screening shall be maintained in a healthy condition. Vegetation used for screening that dies shall be replaced within six months. Fences and walls over six feet high require a building permit. Vehicles may not be stored on streets or public rights-of-way. Screening shall not be placed in the public right-of-way or in the vision clearance triangle of intersections and curb cuts.

d.

Noncomplying Storage. All storage, existing on the adoption date of the ordinance codified in this section,* shall comply with the standards of this code by December 31, 1999. No noncomplying storage conditions will be permitted to be grandfathered in after December 31, 1999.

10.

Wayside stands must be located so as to provide for adequate off-street parking spaces and safe ingress and egress to the adjacent street.

11.

Junk yards, scrap heaps or refuse piles are prohibited, except as specifically permitted in Chapter 20.54.

12.

Minor accessory additions to existing public facilities will be considered as accessory uses not requiring special use permit. Such minor accessory uses include a water tower or small shed at a fire station, or construction of a cover over a playfield at a school or park, but not construction of a new wing to a building, nor construction of a major new building or structure on the site.

13.

On-site treatment and storage facilities for hazardous wastes are allowed as accessory uses in the heavy industry (HI), light industrial (LI), planned industrial park (PI), arterial commercial (AC), and neighborhood convenience (NC) districts. Such facilities are subject to the state siting criteria adopted pursuant to the requirements of Chapter 70.105 RCW.

(Ord. 11804, 1998; Ord. 13884 § 12, 2007; Ord. 13834 § 13, 2007; Ord. 12814 § 2, 2002; Ord. 12463 § 15, 2001; Ord. 11804 § 86, 1998; Ord. 11398 § 3 (part), 1997: Ord. 11220 § 10, 1996: Ord. 11025 § 24, 1995: Ord. 10595 § 52, 1994: Ord. 8970 § 4, 1988: Ord. 8216 § 105, 1985; Ord. 6708 § 3 (part), 1980)

(Ord. No. 14182, § 3, 12-29-2008; Ord. No. 14439, § 6, 11-16-2010; Ord. No. 15952, § 1(Att. A, § VI), 12-15-2020; Ord. No. 16575, § 2(Att. A.XXXIII), 12-16-2025; Ord. No. 16590, § 5(Att. E.IV), 12-16-2025)

Editor's note— See note at § 20.34.030.