Seattle Shed Permits: The 120 Sq Ft Rule and Fees

Do you need a shed permit in Seattle?

Seattle exempts a shed from a building permit only when all six of these are true:

• The projected roof area is 120 square feet or less
• It is a one-story building
• It sits on a simple concrete slab, pier blocks, or soil, not a foundation
• It is not attached to the house or another building
• It is not in or near an environmentally critical area
• It is used only for storage, growing plants, or similar unoccupied uses

Miss any one and you need a permit. For statewide context, see our Washington shed permit guide, and for the national baseline, the complete shed permit guide.

Seattle's threshold is the thing to notice. Much of the country works from a 200 square foot exemption, and Washington does not amend that part of the residential code at the state level, so Seattle's 120 square feet is a local tightening. A 10 by 12 shed, the single most common size sold, sits exactly on Seattle's line where it would be comfortably exempt elsewhere in the state.

The 120 square feet is measured at the roof

The Seattle Residential Code exempts a one-story detached accessory building where the projected roof area does not exceed 120 square feet. Projected roof area, not floor area.

That distinction decides real projects. A 10 by 12 shed has exactly 120 square feet of floor. Add a 12-inch eave overhang on all four sides and the roof projects roughly 12 by 14, or 168 square feet, and the shed needs a permit even though the floor never changed. If you are buying a prefab shed, the roof dimension is the number that matters.

One wrinkle worth knowing: SDCI's plain-language pages are not perfectly consistent. Its sheds page says "120 square feet or less" while another page says "less than 120 square feet." The adopted code says does not exceed 120 square feet, which means exactly 120 is exempt. If your shed lands exactly on the line, confirm with SDCI before you build.

What pushes a shed off the simple permit track

Most sheds that do need a permit only need a subject-to-field-inspection permit, which is Seattle's light-touch path: SDCI screens the application rather than doing a full plan review, and issues some simple permits within 48 hours. Screening itself takes a few days.

Three things knock a shed off that track and onto a full construction addition or alteration permit:

• The shed is in or near an environmentally critical area
• The shed is larger than 750 square feet
• The shed has beams spanning more than 14 feet

That escalation is expensive in time, not just money. SDCI's own published performance for single family addition and alteration permits shows a 30-day goal against a 64-day actual at the 75th percentile, measured in calendar days under city control, and SDCI notes the total time an applicant experiences is roughly twice the days in city control.

A critical-area lot also triggers documents: a topographic survey is required for exterior work on a site with a steep slope or known slide, and a geotechnical report for steep slope, potential or known slide, liquefaction, landfill, or peat settlement prone areas. If your project needs either document, it cannot use the subject-to-field-inspection path at all.

Seattle shed height and the shed roof trap

Height in Seattle is a zoning limit, not a permit trigger, so it applies whether or not you need a permit. Accessory structures located in required setbacks are capped at 12 feet.

Here is the trap, straight from the municipal code: the ridge of a pitched roof may extend up to 3 feet above that 12-foot limit provided every part above the limit is pitched at 4:12 or steeper, but no portion of a shed roof is permitted to extend beyond the 12-foot limit. A single-slope roof, the style most people call a shed roof, gets no bonus at all. A gable at 4:12 gets three extra feet. Same building, same footprint, three feet of difference decided by roof shape.

Where a Seattle shed can sit

Seattle rewrote this part of its code in 2025, when Ordinance 127376 replaced the old single-family zones with Neighborhood Residential (NR1, NR2, NR3) and restructured the development standards. Some of SDCI's plain-language project pages have not caught up with the code, so the numbers below come from the municipal code rather than the summary pages.

Base setbacks for a typical lot are 15 feet front, 15 feet rear where the lot does not abut an alley, and 5 feet average with a 3-foot minimum on the sides. Smaller lots inside frequent transit service areas get 5 feet rear and 3 feet side.

But a shed is governed by a specific accessory-structure rule that is more generous. A structure that is not a dwelling unit may sit inside the rear setback as long as it:

• Is not within 5 feet of a rear lot line, unless that line is an alley lot line, in which case there is no rear setback at all
• Is not more than 12 feet tall
• Is separated from the house by at least 3 feet, eave to eave

So an alley-facing Seattle lot can put a shed right at the back line. A non-alley lot keeps 5 feet.

There is also a neighbor option: an accessory structure may be built in a side or rear setback that abuts the neighbor's setback if the two owners record an agreement with the King County Recorder. That is what SDCI means when it says a setback agreement may be required.

Lot coverage is 50 percent of the lot for structures on a normal residential lot. The 60 percent figure that appears on some SDCI pages applies only to specific configurations inside frequent transit service areas or to stacked dwelling units, not to a typical house with a shed.

Environmentally critical areas void the exemption

This is the second half of what makes Seattle different, and it catches a lot of hillside lots. Critical areas include steep slope erosion hazards, known and potential landslide areas, liquefaction and peat settlement prone soils, seismic hazard areas, flood prone areas, wetlands, riparian watercourses and the land within 100 feet of them, and abandoned landfills.

If any of that touches your property, the 120 square foot exemption disappears and the shed needs a permit no matter how small it is. SDCI states it plainly: work in an environmentally critical area requires a permit and inspections.

You can check your address on SDCI's online map by turning on the critical areas layer, but read the city's caveat carefully: most of those maps are advisory, and your property may have critical areas that are not shown. Critical areas also shrink the lot area used to compute your coverage limit.

Tree protection decides the rest

Seattle's tree protection code is unusually strict and it directly controls where a shed can go. The city defines a tree protection area using the trunk diameter method: a radius of one foot for every inch of trunk diameter at standard height. A 24-inch tree therefore projects a 24-foot-radius protected circle.

Two consequences most homeowners miss:

• Required tree protection areas, and any strip between a protection area and a setback that is less than 10 feet wide, are not considered buildable area. A narrow leftover gap is simply unusable.
• Neighboring trees count. SDCI evaluates the sum of all tree protection areas on the lot, including those cast by off-site trees, not tree by tree.

There is one relief valve: a structure may extend into front and rear setbacks where necessary to protect trees.

What a Seattle shed permit costs

SDCI does not publish a flat shed fee. It publishes a formula, and the input is a construction value that SDCI determines using ICC building valuation data, not a number you choose.

The permit fee for a subject-to-field-inspection permit is 100 percent of the development fee index, the plan review fee is another 40 percent of it, and a 5 percent technology fee applies on top. SDCI publishes no shed fee and no shed construction value, and the code leaves the value for the Director to set, so there is no honest way to state a dollar range in advance. Run your own project through SDCI's fee estimator rather than budgeting from a figure you read anywhere, this page included.

A permit is valid for 18 months from issue.

Historic districts and building without a permit

Seattle has eight historic districts, among them Ballard Avenue, Columbia City, Harvard-Belmont, Pike Place Market and Pioneer Square. Inside them, a Certificate of Approval from the Department of Neighborhoods is a separate authorization from any SDCI permit, required before changing the external appearance of a site or constructing a new structure. The city's published timeline runs to 45 days from a determination of completeness. If you are in a district, ask the Department of Neighborhoods first, because the trigger is written broadly and does not carve out permit-exempt work.

As for skipping the permit: Seattle states the penalty directly, and it is up to $500 per day. SDCI can also issue a stop work order and require a final inspection approval before the work is considered legal. Given how many Seattle lots carry a mapped critical area or a protected tree, the more common outcome is not a fine but a shed that has to move.