Seattle ECA Review for Concrete Projects: When It's Required

Many Seattle lots - particularly in the hillside neighborhoods that need concrete work most often - sit inside or next to one or more Environmentally Critical Areas (ECAs). When a concrete project disturbs soil, changes drainage, or adds structure on an ECA property, additional SDCI review applies under Seattle Municipal Code Chapter 25.09. This guide explains what ECA types exist, how to check the ECA map for your property, which concrete projects trigger review, and how to plan around it. It is part of our Seattle concrete permits hub.

What an ECA is

The City of Seattle regulates land types that need extra care during permitting. Each type carries different rules, but the goal is the same: protect people, property, and resources - soil, water, habitat - from preventable harm. SDCI lists these ECA types under SMC 25.09:

• Geologic hazard areas - landslide-prone, liquefaction-prone, peat settlement-prone, seismic hazard, steep slope erosion hazard (slopes of 40 percent or more), and volcanic hazard areas.
• Flood-prone areas.
• Wetlands.
• Fish and wildlife habitat conservation areas - including riparian watercourses and riparian management areas, the land within 100 feet of a riparian watercourse. SDCI ECA
• Abandoned landfills.

Because some ECAs include buffer or management areas, you do not have to sit directly on a mapped feature to be affected.

How to check whether your lot is in an ECA (Seattle ECA map)

SDCI publishes ECA boundaries as a layer on its online property map. To check a lot:

1. Open the map. Go to the SDCI Property Information (GIS) map, linked from SDCI's "Research a Project, Permit, or Property" page.
2. Find the parcel. Enter the address, or zoom to the property on the map.
3. Turn on the ECA layer. Open the Layer List and switch on Environmentally Critical Areas. Use the help (?) icon if you need navigation tips.
4. Read each ECA type. Look for steep slope, landslide-prone, liquefaction-prone, peat settlement-prone, flood-prone, wetland, riparian, and abandoned landfill areas on or near the parcel lines.
5. Check the site history. Run the address through SDCI's Permit & Site History Research Tool for the Site Characteristics Report and past permits on the lot.
6. Treat the map as a screen, not a ruling. SDCI says most ECA maps are advisory. It confirms an ECA with site-specific information such as a topographic survey or wetland report, some ECA types (such as peat settlement-prone areas) are identified from the maps, and unmapped ECAs can still exist on a property.

If anything shows up on or next to your lot and the project involves excavation, grading, or structure, assume ECA rules apply until SDCI says otherwise.

Concrete projects that typically trigger ECA review

Project	ECA review likely?
Retaining wall or rockery on an ECA parcel	Yes - SDCI requires a permit at any height, and small project waivers don't apply SDCI Tip 327B
Foundation work in a landslide-prone area	Yes - geotechnical and structural review
New hard surface (patio, driveway expansion) in an ECA or buffer	Yes - runoff and infiltration
Grading, excavation, or vegetation removal in an ECA or buffer	Yes - soil stability and habitat
Drainage discharging toward a riparian watercourse	Yes - water quality and habitat
On-grade patio or slab that would normally be permit-exempt	Possibly - SDCI's usual exemptions don't apply on ECA properties; confirm SDCI
Work that may qualify for an exemption or small project waiver	Request it through SDCI (Tips 327A and 327B) Tip 327A Tip 327B

What ECA review adds to the permit

1. Site reconnaissance: confirm ECA type(s) on the lot, photograph existing conditions.
2. Specialist studies: geotechnical report for slopes and soils; wetland or habitat reports for wetland and habitat ECAs.
3. Mitigation or avoidance design: where the project can be moved out of the ECA or buffer, do so; where it cannot, design mitigation.
4. Submittal: studies and drawings go to SDCI as part of the main permit application.
5. Review: SDCI reviews ECA requirements alongside the rest of the permit; revisions may be requested.
6. Construction monitoring: some approvals call for a qualified professional on site during ground disturbance.
7. Final sign-off: inspections confirm the work and any mitigation were built as approved.

Geotechnical reports and slope stability

The most common ECA study for concrete work is the geotechnical report. SDCI's construction permit checklist for ECAs lists a geotechnical report for several ECA categories, and for steep slope areas SDCI may require one even when a small project waiver applies. SDCI ECA checklist For steep-slope or landslide-prone sites the report typically includes a slope-stability evaluation of loads, soil strength, and groundwater. The geotechnical engineer's recommendations then feed the structural design: footing depth, drainage routing, surcharge limits, retaining-wall design. Budget the report separately from the SDCI permit fee. For basement-specific structural review, see the basement and structural permit guide.

Pacific Northwest factors

West Seattle, Magnolia, Queen Anne, parts of Capitol Hill, and many of the city's hillside corridors overlap with steep-slope and landslide-prone ECAs. PNW winters saturate clay-rich soils for months, and a project that looked stable in August can introduce a winter slide risk if drainage is not designed correctly. Treating ECA review as part of the project - not as friction at the end - produces a build that performs in wet seasons. For walls on these lots, see our retaining wall permit guide; for paving, see Seattle's stormwater rules for driveways and patios.

Frequently asked questions

What is an Environmentally Critical Area in Seattle?

Environmentally Critical Areas (ECAs) are land types that Seattle regulates under SMC Chapter 25.09 through additional permit review. They include geologic hazard areas (landslide-prone, liquefaction-prone, peat settlement-prone, seismic, steep slope erosion, and volcanic hazard areas), flood-prone areas, wetlands, fish and wildlife habitat conservation areas such as riparian corridors, and abandoned landfills. Building on an ECA property triggers additional design, study, and inspection requirements through SDCI.

How do I check if my property is in an ECA?

Open SDCI's Property Information (GIS) map, enter your address, and turn on the Environmentally Critical Areas layer in the Layer List. Then check each ECA type on or near your parcel lines. SDCI says most ECA maps are advisory: it confirms an ECA with site-specific information such as a topographic survey or wetland report, and unmapped ECAs can still exist, so confirm with SDCI before relying on the map for permit planning.

Does every concrete project in an ECA need review?

Not every project, but SDCI's usual permit exemptions, such as those for on-grade patios and slabs, don't apply on a property in an ECA, and a retaining wall of any height on an ECA parcel needs a permit. Some work can qualify for an ECA exemption or a small project waiver under SDCI Tips 327A and 327B. Ask SDCI before assuming a small job is exempt.

How long does ECA review take?

ECA requirements are reviewed as part of the SDCI permit, so they add review items rather than a separate fixed timeline. SDCI publishes overall review times on its Construction Permit Performance page. Required studies, such as a geotechnical report, need to be finished before you submit, so start them early.

What studies does ECA review typically require?

Geotechnical reports are common for geologic hazard areas, covering soil, slope stability, and groundwater, and SDCI's ECA construction checklist lists one for several ECA categories. Wetland and habitat ECAs may require a wetland or habitat report and a mitigation plan. Licensed professionals prepare these studies, and they become part of the SDCI permit record; a contractor's opinion can't substitute for them.

Sources

• SDCI – Environmentally Critical Areas (ECA) Code
• SDCI – Property Information (GIS) map with ECA layer
• SDCI – Research a Project, Permit, or Property
• SDCI – Permit & Site History Research Tool
• SDCI Tip 327A – ECA Exemptions and Relief from Steep Slope Prohibition
• SDCI Tip 327B – ECA Small Project Waivers
• SDCI – Construction Permit Checklist: Environmentally Critical Areas
• SDCI – Do You Need a Permit?

Plan the ECA review into the project timeline

The earliest action on an ECA-affected lot is the map check and a site walk with a contractor and engineer. A free on-site assessment confirms which ECA types apply, what studies will be needed, and how to sequence the work so the permit timeline lines up with the build. Call (206) 552-9998 or browse retaining wall services and concrete foundation services for the project types most often affected by ECA review.