Thurston County, WA Zoning Overlays & Bonuses: Density Bonus Law (2026)
Key Facts
- Density bonus
- 50% above base zone density
- Where allowed
- Residential 3-6 and 4-16 districts only
- Condition
- All units LEED/Passive House/Built Green
- Stacking
- No other density bonus applies
- Cluster size
- 2 to 12 dwellings per cluster
Summary
Thurston County allows a cottage housing development to exceed its underlying zone's density by fifty percent under Code Section 20.38.030(B)(1), but only if every dwelling in the project is built to a recognized green building standard such as LEED, Passive House, or Four Star Built Green. Cottage developments cannot stack any other density bonus available in the underlying zone on top of this one.
B.Density. The density of the underlying zone governs unless a density increase is granted as provided in this chapter. Other density bonuses found in the underlying zone shall not apply to cottage developments.1.Density Increases. Cottage housing developments may exceed the density of the underlining zone by fifty percent when the development is in compliance with all standards of this chapter and if all dwellings are constructed in accordance with a green building certificate program such as LEED (Leadership in Energy and Environmental Design), Passive House, and Four Star Built Green.
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: Code of Ordinances: Supplement 77).
Full Breakdown
020. 030(B) starts from the underlying zone's base density and holds cottage projects to it unless the fifty-percent increase in subsection (B)(1) is granted, and it expressly turns off any other density bonus that zone might otherwise offer, so the green-building bonus is the only path to added density for a cottage project. 38's cottage standards: a minimum two and maximum twelve units per cluster, gross floor area capped at 1,200 square feet per cottage with a 1,000-square-foot footprint limit, garages capped at 225 square feet, ten percent common and private open space meeting minimum dimension and configuration rules, a twenty-five-foot height limit for cottages, and one and one-half parking spaces per dwelling.
Because the bonus is conditioned on actual certification rather than a stated design intent, the county can confirm compliance against the specific certifying body's standard when reviewing the site plan and again before issuing certificates of occupancy for the additional units the fifty-percent increase makes possible.
Violations & Fines
A cottage housing project that claims the fifty-percent density increase without every unit achieving its stated green building certification, or that otherwise fails to meet Chapter 20.38's cluster, floor area, open space, height, or parking standards, is not entitled to build at the bonus density; the county can hold approval to the underlying zone's base density, or condition final approval on documented certification, until compliance with Section 20.38.030 is demonstrated.
Frequently Asked Questions
How much extra density can a cottage housing project get in Thurston County?
Can I combine the cottage housing density bonus with another zoning bonus?
Where in Thurston County can I build cottage housing at all?
Sources & Official References
Other rules in Thurston County
Compare Thurston County to another location·View the Washington zoning overlays & bonuses overview
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