Snohomish County's unincorporated permit zone covers everything from the Edmonds waterfront to rural acreage near the Cascade foothills. The rules reflect that range: suburban properties near Everett get the standard 200 sq ft shed exemption, while rural properties outside the Urban Growth Area can build up to 400 square feet without a permit.
But even "permit-free" has limits. Every project—exempt or not—must comply with zoning setbacks. And any project that adds new hard surface (even a small patio) triggers a stormwater documentation requirement.
Do You Need a Site Plan for a Small Permit in Snohomish County?
Yes. If your project in unincorporated Snohomish County requires a building permit, a site plan is required.
The PDS site plan checklist requires your plan to include:
- Site boundary and property dimensions with accurate lot area.
- A scale using a standard engineer's scale (1"=10', 20', 30', 40', 50', 60', 100', or 200').
- A North arrow.
- Existing and proposed structures with dimensions and locations.
- Setbacks (distance from all property lines to all structures).
- Easements and rights-of-way.
- Contour lines and existing topography.
- Utilities (water, sewer, septic, gas, electricity).
- Fire hydrant location (nearest hydrant if served by a water purveyor).
- Ditches, streams, and drainage courses.
- Critical areas (wetlands, streams, steep slopes, floodplains within 300 feet).
- Fill and cut totals.
- Impervious surface (existing and proposed square footage).
Paper requirements: Site plans must be on plain white paper (8.5"×11", 8.5"×14", or 11"×17"). Do not use graph paper.
Who Runs Into This in Snohomish County
- Edmonds and Marysville residents who apply to the Snohomish County PDS portal, only to be redirected to their city's own building department.
- Rural homeowners who build a 450-square-foot barn assuming the rural exemption covers it, not realizing the threshold is 400 sq ft outside the UGA (and with sidewalls under 11 feet).
- Suburban homeowners who add a 1,500 square foot concrete driveway, not realizing this triggers a Small Project SWPPP requirement even though the project doesn't seem "large."
- DIYers who draw their site plan on graph paper, resulting in an automatic rejection at the permit counter.
What Needs a Site Plan in Snohomish County
- Fence permit site plan — Fences over 8 feet require a permit. (Fences under 8 feet are exempt—this is more generous than many neighboring counties).
- Shed permit site plan — Required for sheds over 200 sq ft (inside UGA) or over 400 sq ft (outside UGA). The structure must also have sidewalls under 9 feet (UGA) or 11 feet (outside UGA) to qualify for exemption.
- Deck permit site plan — Required for decks attached to a dwelling, or freestanding decks over 30 inches above grade.
- Pool permit site plan — Required for pools and spas. Must show setbacks, barriers, and drainage.
- Garage permit site plan — Required for detached structures exceeding the exemption thresholds.
- Addition permit site plan — Required. Must show expanded footprint, contours, utilities, and drainage documentation.
- ADU — Up to 2 ADUs per single-family lot are allowed by-right under Washington state law.
Why This Trips People Up in Snohomish County
The UGA vs. Rural Shed Exemption. This is unique to Snohomish County. Inside the Urban Growth Area (near Everett, Lake Stevens, Marysville), the standard Washington threshold of 200 sq ft applies. But outside the UGA—in rural areas—you can build a one-story detached accessory structure up to 400 square feet with sidewalls under 11 feet without a building permit. This is a significant benefit for rural property owners.
The 8-Foot Fence Exemption. Most Washington counties exempt fences up to 6 feet. Snohomish County exempts fences up to 8 feet from building permits in unincorporated areas—an unusually generous rule.
Tiered Drainage Documentation. Any new or replaced hard surface triggers stormwater documentation—even small projects:
- 1–1,999 sq ft: Small Project SWPPP (Stormwater Pollution Prevention Plan).
- 2,000–4,999 sq ft: Land Disturbing Activity (LDA) Permit with a Targeted Stormwater Plan.
- 5,000+ sq ft: LDA Permit with Full SWPPP and Drainage Plan.
This means adding a 1,200 sq ft driveway—even if it doesn't require a building permit—still requires a Small Project SWPPP before work begins.
No Graph Paper. The county's site plan checklist explicitly states plans must be on plain white paper. Graph paper is not accepted.
Zoning and Setbacks in Snohomish County
Setbacks are governed by SCC Title 30 and vary by zoning district.
Setback Adjustment Options:
- The county director may reduce property line setbacks by up to 25% for walls or structures 20 feet or less in length.
- When a lot sits between two lots with nonconforming front setbacks, the required front setback may be the average of those two setbacks or 60% of the code requirement.
ADU Setbacks: ADU floor area is capped at 1,200 square feet (excluding garages and porches).
How the Tool Handles This — 5 Steps
SitePlans.ai loads Snohomish County parcel data so you can generate the engineer-scaled site plan on the correct paper size required by PDS:
- Enter your address — Lot lines load from SCOPI parcel data.
- Place your project — Add your shed, deck, or ADU.
- Apply the engineer's scale — Select from standard engineer's scales (1"=20', etc.).
- Calculate impervious surface — Determine your drainage documentation tier.
- Export on plain white paper — Download a properly formatted PDF ready for the PDS Permit Portal.
Where This Tool Fits — and Where It Doesn't
| Situation | Best path |
|---|---|
| Shed, deck, or addition in unincorporated Snohomish County | SitePlans.ai for the required site plan |
| Confirming whether a rural shed qualifies for the 400 sq ft exemption | SitePlans.ai to verify dimensions and setbacks |
| New impervious surface (any size) | SitePlans.ai for layout + verify drainage tier with PDS |
| New home construction | Licensed WA Architect/Engineer required |
| Critical area on or near property | Licensed WA Professional required for critical area study |
What This Doesn't Replace
Our site Plan generator tool helps create preliminary, conceptual site plans for residential projects in unincorporated Snohomish County. It is not a licensed land survey, critical area study, or stormwater engineering plan. If your project is in or near a critical area (wetland, stream, steep slope, or floodplain), you must consult with the Snohomish County PDS before finalizing your site plan.
Comparison: Your Options for a Snohomish County Site Plan
| Method | Cost | Time | Stamp | Notes |
|---|---|---|---|---|
| Hand sketch | Free | 1–2 hrs | ✗ | Must be on plain white paper (no graph paper) at engineer's scale |
| SitePlans.ai | Free first plan | Minutes | ✗ | Generates correctly formatted PDF at engineer's scale |
| CAD drafter | $300–$800+ | 1–2 weeks | Sometimes | Useful for large projects with complex grading |
| Licensed WA Engineer/Architect | $800–$3,000+ | 2–5 weeks | ✅ | Required for critical area studies and new homes |
| SitePlans.us (done-for-you) | Custom | 1–3 days | ✗ | Best if your PDS portal submittal was rejected |
Common Mistakes That Delay Snohomish County Permits
- Using graph paper — Automatic rejection at the permit counter.
- Wrong UGA/rural exemption — Applying the 400 sq ft rural exemption to a property that is actually inside the UGA (where only 200 sq ft applies).
- Missing impervious surface calculation — Forgetting to total up existing and proposed hard surfaces for the drainage tier determination.
- Ignoring the Small Project SWPPP — Adding a 1,500 sq ft driveway without the required stormwater plan.
- Applying to the wrong jurisdiction — Submitting to Snohomish County PDS when the property is inside Everett, Lynnwood, or another incorporated city.
Support and Local Resources
- Snohomish County PDS — snohomishcountywa.gov | Call (425) 388-3311.
- SCOPI Interactive Map — gis.snohomishcountywa.gov/SCOPI/ — verify jurisdiction and parcel data.
- PDS Permit Portal — Submit and track permits online.
- FEMA Flood Maps — msc.fema.gov
Nearby Counties
Frequently Asked Questions
1. How big of a shed can I build without a permit in Snohomish County?
Inside the Urban Growth Area (UGA): up to 200 square feet with sidewalls under 9 feet. Outside the UGA (rural areas): up to 400 square feet with sidewalls under 11 feet. Both exemptions require no electrical or plumbing.
2. How high of a fence can I build without a permit?
Fences under 8 feet in height are generally exempt from building permits in unincorporated Snohomish County—more generous than most neighboring counties.
3. What kind of paper do I need for my site plan?
Plain white paper—8.5"×11", 8.5"×14", or 11"×17". Graph paper is not accepted.
4. When do I need a stormwater plan?
Any new or replaced hard surface triggers stormwater documentation. Even 1–1,999 sq ft of new concrete, asphalt, or roofing requires a Small Project SWPPP.
5. Can I use SitePlans.ai for a Snohomish County permit?
Yes. SitePlans.ai generates the correctly scaled site plan on the proper paper format with impervious surface calculations—ready for the PDS Permit Portal.
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Start Your Snohomish County Site Plan
Verify your jurisdiction on the SCOPI interactive map first. Then enter your address below to pull your property lines, place your project, calculate your impervious surface, and download the plain-white-paper PDF you need for the PDS Permit Portal.
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