Seattle Site Plan Requirements & Permit Guide (2025)

By Site Plan Creator Team •

Everything you need to know about creating site plans for building permits in Seattle, including SDCI requirements, the Land Use Code, and design review.

Seattle Site Plan Requirements: Complete Guide for Building Permits

Creating a site plan for a building permit in Seattle, Washington requires meeting specific requirements set by the Seattle Department of Construction and Inspections (SDCI). Seattle's development is governed by the Seattle Municipal Code (SMC) Title 23 (Land Use Code), with special considerations for environmentally critical areas, tree protection, and the city's progressive mandatory housing affordability (MHA) requirements.

What Is a Site Plan and Why Does Seattle Require One?

A site plan is a scaled drawing showing your property boundaries, existing structures, proposed construction, setbacks, and site features. SDCI requires a site plan for all building permit applications to verify compliance with SMC Title 23 and the Seattle Building Code. Look up your property's zoning through the city's GIS portal at seattle.gov/sdci.

Required Site Plan Elements for SDCI

  • Property boundaries with dimensions and total lot area
  • Setbacks per SMC Title 23
  • Existing and proposed structures with dimensions, height, and use
  • Lot coverage and Floor Area Ratio (FAR) calculations
  • Parking spaces per SMC 23.54 (eliminated in many zones)
  • Tree survey per SMC 25.11 (all trees 6 inches+ diameter)
  • Environmentally Critical Areas (ECA) if present (steep slopes, wetlands, streams)
  • Stormwater management per Seattle Stormwater Code (SMC 22.800-22.808)
  • North arrow and scale
  • King County parcel number

Seattle Zoning and Setback Requirements

  • SF 5000 (Single-Family, 5,000 sq ft lot): Front 20 feet, side 5 feet, rear 25 feet. Lot coverage max 35%. FAR max 0.5. Height max 30 feet.
  • SF 7200 (Single-Family, 7,200 sq ft lot): Front 20 feet, side 5 feet, rear 25 feet. Lot coverage max 35%. FAR max 0.5.
  • LR1-LR3 (Lowrise Multi-Family): Front 7 feet, side 5 feet, rear 15 feet. Lot coverage max 50-60%. FAR 1.0-1.4.
  • MR (Midrise): Front 7 feet, side 7 feet, rear 15 feet. Height max 60 feet.
  • NC (Neighborhood Commercial): Front 0 feet (build-to), side varies, rear 15 feet.

DADU and ADU Requirements

Seattle has been a national leader in ADU policy:

  • Two ADUs allowed per lot: One attached ADU (within the primary dwelling) and one Detached Accessory Dwelling Unit (DADU) permitted on any single-family lot
  • DADU size: Up to 1,000 sq ft
  • DADU height: Up to 22-25 feet depending on rear lot line conditions
  • Setbacks: 5 feet from side and rear for DADUs
  • No additional parking required for ADUs or DADUs
  • No owner occupancy requirement
  • Pre-approved DADU plans: SDCI offers pre-approved standard plans for faster permitting

Tree Protection Requirements

Seattle's Tree Protection Ordinance (SMC 25.11) requires:

  • Tree survey: All trees 6 inches+ diameter must be shown on the site plan
  • Exceptional trees: Trees 24 inches+ diameter or trees of particular species at smaller sizes are classified as exceptional and have the highest protection
  • Tree removal permits: Required for removing trees 6 inches+ diameter in single-family zones
  • Replacement: Removed trees must be replaced at specified ratios or payment into the Tree Fund
  • Tree protection during construction: Required barriers at the drip line of retained trees

Environmentally Critical Areas (ECAs)

Seattle has extensive ECAs that significantly affect development:

  • Steep slopes (40%+): Development restricted; geotechnical study required
  • Landslide-prone areas: Enhanced setbacks and engineering required
  • Wetlands and streams: Buffers of 50-300 feet depending on wetland class
  • Peat settlement-prone areas: Special foundation requirements
  • Shoreline areas: Additional regulations under the Shoreline Master Program
  • Your site plan must identify all ECAs and show required buffers and setbacks

Mandatory Housing Affordability (MHA)

Seattle's MHA program requires most new commercial and multi-family development to contribute to affordable housing:

  • Performance option: Include affordable units within the development
  • Payment option: Pay a per-square-foot fee to the city's affordable housing fund
  • MHA contributions are required in zones that received additional development capacity through upzones

Stormwater Management

  • Seattle Stormwater Code: Among the most comprehensive in the nation
  • Threshold: Projects adding 750+ sq ft of impervious surface require stormwater management
  • Flow control and treatment: Required for regulated projects using rain gardens, bioretention, permeable pavement, or cisterns
  • Green infrastructure: Seattle's RainWise program offers rebates for rain gardens and cisterns on private property

How to Submit

Seattle Services Portal

Submit through SDCI's online portal at cosaccela.seattle.gov for electronic plan review.

In-Person

Walk-in at 700 5th Avenue, Suite 2000.

Permit Fees and Timeline

  • Fees: Per SDCI fee schedule; includes MHA payments for qualifying projects
  • Timeline: Simple residential (pre-approved DADU) 4-6 weeks. Standard residential 6-12 weeks. Commercial 3-6 months. Design review adds 3-6 months. SEPA review for larger projects adds additional time.

Creating Your Seattle Site Plan with Site Plan Creator

Site Plan Creator makes it easy to generate a professional, permit-ready site plan for your Seattle property. Simply enter your address, and the tool automatically loads your property boundaries, building footprints, and aerial imagery. You can then add setback lines, label structures, draw proposed construction, and export a scaled PDF ready for SDCI submission.

Frequently Asked Questions

What are the typical residential setbacks in Seattle?
In SF 5000 zones, front setbacks are 20 feet, side 5 feet, rear 25 feet with 35% lot coverage and 0.5 FAR. LR lowrise zones have 7-foot front setbacks and 50-60% coverage. NC commercial zones use build-to lines with zero front setbacks. Check SDCI's GIS portal for your zone.
Can I build an ADU and DADU on my lot?
Yes, Seattle allows two ADUs per single-family lot: one attached and one detached (DADU). DADUs can be up to 1,000 sq ft with 22-25 foot height. No additional parking or owner occupancy required. SDCI offers pre-approved DADU plans for faster permitting (4-6 weeks vs. 6-12 weeks).
What tree protection is required?
All trees 6 inches+ diameter must be surveyed and shown on site plans. Exceptional trees (24 inches+ or specific species at smaller sizes) have the highest protection. Tree removal permits required in SF zones. Removed trees need replacement or Tree Fund payment. Construction barriers required at drip lines.
What are Environmentally Critical Areas?
ECAs include steep slopes (40%+), landslide-prone areas, wetlands, streams, peat settlement areas, and shoreline areas. They require special studies, enhanced setbacks, and buffers (50-300 feet for wetlands). ECAs can significantly limit buildable area. Your site plan must identify all ECAs.
What is Mandatory Housing Affordability?
MHA requires most new commercial and multi-family development to include affordable units (performance option) or pay per-square-foot fees (payment option) to the city's affordable housing fund. MHA applies in zones that received additional development capacity through upzones.
What stormwater management is required?
Projects adding 750+ sq ft of impervious surface need stormwater management. Flow control and water quality treatment required using rain gardens, bioretention, permeable pavement, or cisterns. Seattle's RainWise program offers rebates for rain gardens and cisterns.
How do I submit plans to SDCI?
Submit through SDCI's online portal at cosaccela.seattle.gov. Walk-in at 700 5th Avenue, Suite 2000. Pre-approved DADU plans process in 4-6 weeks. Standard residential takes 6-12 weeks. Design review for larger projects adds 3-6 months.
How long does Seattle plan review take?
Pre-approved DADU: 4-6 weeks. Standard residential: 6-12 weeks. Commercial: 3-6 months. Design review adds 3-6 months. SEPA environmental review for larger projects adds additional time. Seattle's review times are longer than many cities due to comprehensive environmental review.

How to Create a Site Plan in Seattle

  1. Look Up Your Property Information: Use SDCI's GIS portal to find zoning, FAR, lot coverage, ECAs, tree protection requirements, and MHA status. Note your King County parcel number.
  2. Assess Environmental Constraints: Identify ECAs (steep slopes, wetlands, streams, landslide areas), tree survey needs, stormwater requirements, and any shoreline regulations.
  3. Create Your Site Plan: Enter your Seattle address in Site Plan Creator to load property boundaries, building footprints, and aerial imagery. Add setback lines per SMC Title 23.
  4. Include All Required Elements: Include boundaries, setbacks, lot coverage, FAR, tree survey (all trees 6 inches+), ECAs with buffers, stormwater features, parking (if required), and north arrow with scale.
  5. Prepare Supporting Documents: Prepare tree survey and arborist report. For properties with ECAs, prepare geotechnical or wetland studies. Prepare stormwater management plans.
  6. Submit Through SDCI Portal: Upload plans through cosaccela.seattle.gov. Pay fees. Consider pre-approved DADU plans for faster processing.
  7. Manage Review and Obtain Permit: Respond to SDCI comments. Navigate design review if required. Once approved, pay remaining fees and MHA contributions, receive permit, and schedule inspections.