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Thurston County ACCESSORY DWELLING UNIT OPTIONS

DRAFT May, 2018

Thurston County is developing standards to allow accessory dwelling units (ADUs) in the rural areas of Thurston County.

An ADU is a small, separate living unit built on the same lot as a single family home. It can be a conversion of a basement, garage or addition to an existing home. An ADU has all the basic facilities for day-to-day living, such as a kitchen, sleeping area, and bathroom.

What issues do ADUs address?

• Increase the supply of affordable housing, without creating urban sprawl.

• Offer housing to extended family who want to remain close, but need independence.

• Provide an alternative for senior homeowners to “age in place.”

• Supplement homeowners income with a low maintenance rental unit.

• Design standards and requirements maintain rural character and ensure neighborhood character is preserved.

The following information includes the 3 primary ADU policy options staff is recommending for consideration, as well as Q&A regarding detached ADU options.

Option 1 is attached ADUs only, and options 2 & 3 include variations to allow detached ADUs.

Current County Policy

ADUs are currently

allowed in Olympia, Lacey

and Tumwater, as well as

many Urban Growth

Areas. ADUs are not

currently allowed in the

rural County.

Family Member Units

(TCC 20.09.030)

In the rural County, one

temporary mobile/

manufactured or modular

home is permitted, for the

purpose of housing a

family member.

The unit must be removed

once the family member

leaves. However, this

policy is hard to enforce.

Staff Contact Krosbie Carter, Associate Planner

360-786-5505 | carterk@co.thurston.wa.us

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Thurston County ACCESSORY DWELLING UNIT OPTIONS

DRAFT May, 2018

Standards that apply to ALL Accessory Dwelling Unit (ADU) options

• Attached ADUs allowed.

• No more than 1 ADU per lot.

• Permitted everywhere a single-family home can be.

• ADUs shall comply with all applicable building, plumbing, mechanical, fire, health, and other applicable codes and permits.

• An ADU must be served by an approved on-site sewage system and drinking water supply as outlined in the Thurston County Sanitary Code and applicable Washington State Administrative Codes.

• The primary single-family unit and the ADU together shall conform to the standards of the zone, including but not limited to coverage and setbacks.

• Attached ADUs shall not be considered as a dwelling unit when calculating density.

• The total floor area of a basement may be used for the ADU, provided there is a separate exterior entrance, and the conversion does not exceed the size of the primary dwelling unit.

• The ADU must substantially maintain the appearance of the single-family structure.

Standards that apply to all DETACHED options only:

• Allow a reasonable deviation in size to accommodate mobile, modular or manufactured homes being used as a detached ADU, provided it is still smaller than the primary home.

• If a manufactured home is used as detached ADU screening (i.e. landscaping) is required to address rural compatibility issues.

The main variations for each detached option include:

• Size of legal lot allowed to have a detached ADU.

• Owner occupancy requirement.

• Conversions of existing detached accessory structures (i.e. garage, guest house). “Existing” is defined as already built or the permit issued at the time of adoption of the ordinance.

• Size of the ADU.

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Thurston County ACCESSORY DWELLING UNIT OPTIONS

DRAFT May, 2018

Option 1: Attached Only

• Attached ADUs only

• Require owner occupancy of either

the primary house or ADU

• Maximum size of 1,000sf, but still

subordinate in size to the primary

home

Attached allowed

on all lots

• Size options for the ADUs include:

- Size in Option 1: One set size (i.e. no larger than 1,000sf).

- Size in Option 2: Sliding scale based on the percentage of the primary dwelling (i.e. larger houses allowed larger ADU, but generally not smaller than 800sf).

- Size in Option 3: The total floor area of the ADU is limited to a maximum of 1,500 square feet or 50% of the primary dwelling, whichever is less.

If the floor area of the single-family dwelling unit is:

The floor area of the ADU shall not exceed:

Under 2,000sf 40%

2,000sf or more, but less than 3,000sf 35% or 800sf, whichever is greater

3,000sf or more, but less than 5,000sf 30% or 1,050sf, whichever is greater

Over 5,000sf 20% or 1,500sf, whichever is greater

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Thurston County ACCESSORY DWELLING UNIT OPTIONS

DRAFT May, 2018

10 -acre property in the RRR 1/5 zone with new detached ADU

...could help

reduce this

Option 2: detached on 10+ acres only

• Allow detached ADUs on legal lots that meet the underlying density requirements, provided the legal lots are 10 acres or more. Prohibit future subdivision through an affidavit, which follows the property after a sale.

• Size: A sliding scale based on the percentage of the primary dwelling unit.

• Require owner occupancy for at least 6 months of the year.

Option 3: detached on all properties that meet underlying density

• Allow detached ADUs on all legal lots that meet the underlying density requirements. Prohibit future subdivision through affidavit which follows the property after a sale.

• Existing detached accessory structures can be converted to a detached ADU, without counting towards density (see the Q&A for explanation)

• Size: The total floor area of the ADU is limited to a maximum of 1,500 square feet or 50% of the primary dwelling, whichever is less.

• No owner occupancy requirement

Option 2 & 3

10-acre property in the RRR1-5 zone. Subdivided into two 5-acre properties, with two full houses

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Thurston County ACCESSORY DWELLING UNIT OPTIONS

DRAFT May, 2018

Detached Accessory Dwelling Units (ADUs)

Q&A

Q: Why do detached ADUs county toward density but attached do not?

Newly built detached ADUs count towards density because a freestanding detached ADU is not structurally different than a single-family home. That is why it is counted as a separate dwelling unit.

An attached ADU is part of the structure (either as an addition or internal conversion, such as a basement) of a single-family home, and doesn’t generally look different than the primary house.

Even though both types of ADUs would have the same basic use and function, in this case, density and rural character focuses on how many separate dwelling units are on a singular property.

5-acre property in the RRR1/5 zone with attached ADU.

Part of main house.

5-acre property in the RRR1/5 zone. Second freestanding house not allowed

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Thurston County ACCESSORY DWELLING UNIT OPTIONS

DRAFT May, 2018

Q: What is a lot that “meets the underlying density of the zone”?

These are lots that have twice the amount of acreage necessary to build a single house, based on the zoning of the property.

For example, RRR 1/5 is the most common zoning in rural Thurston County; this means that one house is allowed per 5 acres, and no ‘new’ lot should be smaller than 5 acres if subdivided. Only allowing 1 house per 5 acres is the density of your property.

However, no matter the size of a property, only one single-family house is allowed per legal lot. If a property owner has 10 acres in an RRR 1/5, they could pay to subdivide the property into two 5-acre parcels and then build two large single-family homes.

Because of this, the existing 10-acre lot is considered to have double the acreage necessary to build a one single-family home and meet the underlying density of the zone. The same could apply to a 4 acre property in the RL 1/2 (1 house per 2 acres). Detached ADUs may only be allowed on lots that have double the acreage necessary to meet the density of the zone.

10-acre property in the RRR1/5 zone.

Subdivision potential into two 5-acre lots

5-acre property in the RRR1/5 zone.

Only 1 house allowed

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Thurston County ACCESSORY DWELLING UNIT OPTIONS

DRAFT May, 2018

Q: Why are detached ADUs only allowed on properties that meet the underlying density of the zone?

Detached ADUs typically count towards the ‘density’ of your property, and are considered to be structurally the same as a larger home. If you own 5 acres in an RRR 1/5, and already have a large single-family home on the property, you aren’t allowed to build a second home.

However, a 10-acre property is considered to have double the acreage necessary to meet the underlying density of the zone in the RRR 1/5. A detached smaller house on the 10-acres would not exceed 1 house per 5 acres, and would meet the density of the underlying zone.

In order to build a detached ADU on a 10-acre property without paying to subdivide first, an owner will need to sign an affidavit that prohibits future subdivision. This keeps the 10-acres intact, without creating two 5-acre properties. Allowing property owners to build a smaller detached ADU on these types of lots:

• Helps to preserve these lots from larger development, as detached ADUs must be smaller than the primary home, and would have less of an impact on the natural environment and rural character of the area than subdividing and building a second house.

• Allows homeowners to utilize their property to accommodate their family needs. Many homeowners want to build smaller houses for family or to help them ‘age in place’ as they get older.

10-acre property in the RRR155 zone with new detached ADU. 10-acre property in

the RRR1/5 zone. Subdivided into two 5-acre properties, with two full houses

...can help

reduce this

So that

this...

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Thurston County ACCESSORY DWELLING UNIT OPTIONS

DRAFT May, 2018

5-acre property in the RRR1/5 zone with existing detached garage. Minimal impacts to convert to ADU.

5-acre property in the RRR1/5 zone. New construction to build attached ADU. Potential impacts to land, environment.

So that

this...

...can help

reduce this

Q: Why does a new detached ADU count toward density, but a conversion of an existing “accessory structure” does not?

While the new construction of a detached ADU must count towards the density of your property, if you have an existing detached structure (i.e. garage, shop, guest house), you may be eligible to convert it to an ADU even if your property does not meet the acreage requirement.

An “existing structure” means that the building must either have been already built or the permit issued by the Building Development Center by the time the ADU ordinance is adopted. This is to make sure that new detached structures are not built and then later converted to detached ADUs on properties where they may not be allowed. This provision helps balance the rural character and urban sprawl in the rural county.

The reason for the exception is that these buildings have already created an impact on the property and rural land. By allowing these buildings to convert the use (from garage to ADU), property owners can minimize any new or additional impacts which may be created by building an attached ADU on their home.

This concept is based on existing Growth Management Hearings Board Rulings which have found that conversions of existing structures would not create ‘urban growth’ and could be considered the same as an attached ADU in regards to density.