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Pierce County, WA Accessory Structures: ADU Rules (2026)

Few Restrictions

Compiled from the official code textEditor Martyn O'NeillLast verified July 2026

ADU rules in Pierce County, WA, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.

Key Facts

Governing code: PCC 18A.37.120
Number allowed: 2 in UGA, 1 outside UGA
Max size in UGA: 1,000 sq ft
Max size outside UGA: 1,250 sq ft
Owner occupancy: Not required

ADU Eligibility Quick-Check

An Accessory Dwelling Unit (ADU) is a smaller, independent living unit on the same lot as a single-family home: converted garages, detached cottages, basement or attic conversions, and attached additions all qualify. Most states have streamlined ADU permitting since 2020, but local rules still control size, height, and setback.

Is your lot zoned single-family or multi-family residential?
Does your lot have at least 1,200 sq ft of buildable space?
Is your existing home owner-occupied (in most states this is not required, but some require it for ADU permits)?
Will the ADU stay under your state's size cap (commonly 850-1,200 sq ft for detached)?
Can you provide one off-street parking space (waived in many states within 0.5 mi of transit)?

If you answered 'yes' to most of these, you likely qualify in Washington under recent ADU streamlining laws. The Pierce County, WA rules below cover local size, height, and setback requirements.

Summary

Unincorporated Pierce County allows accessory dwelling units under PCC 18A.37.120. Two ADUs are permitted per lot inside an Urban Growth Area and one outside, attached or detached, with size caps and a building permit.

City-specific rules exist: Lakewood, and Tacoma have their own adu rules rules that differ from Pierce County's county-level regulations. If you live in one of those cities, check the city-specific page instead.

Two ADUs are allowed per lot of record as an accessory use within the Urban Growth Area (UGA) and one ADU outside of the UGA in conjunction with any single-family residential structure in all zones where that use is permitted.

View official code

Official source re-checked September 8, 2026: no newer edition of the code had been published (publisher’s edition: current through Ordinance 2026-515, and legislation passed through May 26, 2026).

Full Breakdown

Pierce County Code 18A.37.120 governs ADUs in unincorporated areas, updated to comply with Washington's HB 1337. Two ADUs are allowed per lot of record inside the Urban Growth Area (UGA) and one ADU outside the UGA, in any attached/detached combination on single-family lots. An ADU may not exceed 1,000 square feet inside the UGA, rising to 1,250 square feet outside the UGA, measured as interior habitable area excluding garages. Owner-occupancy is no longer required, so an ADU may be rented as an investment unit. A building permit is required, and conversion of an existing detached structure to an ADU is allowed within side or rear setbacks inside the UGA.

Violations & Fines

Building an ADU without a permit, exceeding the 1,000/1,250 square-foot cap, or ignoring setback and design standards can trigger stop-work orders, code enforcement, and required corrections or removal.

Frequently Asked Questions

How many ADUs can I build?

Two ADUs per lot of record inside an Urban Growth Area, or one outside, in any attached or detached combination on a single-family lot.

Do I have to live on the property?

No. Pierce County eliminated the owner-occupancy requirement, so neither the main home nor the ADU must be owner-occupied.

Is parking required for an ADU?

No extra off-street space is required within one-half mile of a major transit stop; otherwise parking follows PCC 18A.35.040.

Sources & Official References

Other rules in Pierce County

Shed & Carport RulesSome Restrictions Garage ConversionsSome Restrictions Tiny HomesSome Restrictions ADU Impact FeesSome Restrictions Fence Regulations: Retaining WallsSome Restrictions Fence Regulations: Material RestrictionsSome Restrictions Animal Ordinances: MicrochippingSignificant Restrictions Animal Ordinances: Mandatory Spay/NeuterSignificant Restrictions Animal Ordinances: Pet Store RulesHeavy Restrictions Landscaping Rules: Rainwater HarvestingLight Restrictions

All Pierce County rules

How Pierce County compares: Easiest Cities to Build an ADU·Compare Pierce County to another location·View the Washington accessory structures overview

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ADU Rules in Cities Across Pierce County

Tacoma, WA Lakewood, WA