When does a detached garage need a building permit in Seattle?

Seattle's accessory-building exemption stops at 120 sq ft of roof, so a garage needs a building permit. Only storage structures with 120 sq ft of roof or less are exempt.

Where do I apply for a detached garage permit in Seattle?

Apply through Seattle Services Portal, or call (206) 684-8600.

Do you need a permit for a detached garage in Seattle, WA?

It depends on size and placement.

Building permit: Seattle's accessory-building exemption stops at 120 sq ft of roof, so a garage needs a building permit.

Floodplain development permit: If the lot is in a FEMA special flood hazard area, all development there needs a permit.

Rules last checked by a person on October 19, 2026. Guidance only; confirm with Seattle before you build.

Check your exact lot

Setbacks depend on your zoning district, and a flood zone can change the permit answer. Enter your address to see both.

Permits a detached garage can need in Seattle

Permit	When it applies
Building permit	Seattle's accessory-building exemption stops at 120 sq ft of roof, so a garage needs a building permit.Confidence: medium
Floodplain development permit	If the lot is in a FEMA special flood hazard area, all development there needs a permit.
Electrical permit	Wiring needs its own permit.Confidence: medium

Local details

Call 811 at least a few days before you dig footings or post holes. Utility locating is free.
HOA covenants and deed restrictions can be stricter than city rules. Check yours before you build.

How to apply

Questions people ask

When does a detached garage need a building permit in Seattle?: Seattle's accessory-building exemption stops at 120 sq ft of roof, so a garage needs a building permit. Only storage structures with 120 sq ft of roof or less are exempt.
Where do I apply for a detached garage permit in Seattle?: Apply through Seattle Services Portal, or call (206) 684-8600.

Sources

Seattle SDCI, Sheds. Checked 2026-10-19.
You don't need a permit to build a shed if... the total area (or footprint) of the shed's roof is 120 square feet or less... single-story... sits on a simple concrete slab, pier blocks, or soil... not attached... not in or near an environmentally critical a…
44 CFR 59.1, definition of development (NFIP). Checked 2026-10-19.
Development means any man-made change to improved or unimproved real estate, including but not limited to buildings or other structures...
44 CFR 60.3, floodplain management criteria. Checked 2026-10-19.
Require permits for all proposed construction or other development in the community...
2024 IRC R105.2, Work exempt from permit (text published by the City of Benson, AZ). Checked 2026-10-19.
One-story detached accessory structures, provided that the floor area does not exceed 200 square feet. Fences not over 7 feet high. Decks not exceeding 200 square feet in area, that are not more than 30 inches above grade at any point, are not attached to a…