Walk the lot for ECA, slopes, trees, and poles

What you're looking for

The DADU envelope rules give you the maximum buildable footprint. Trees, ECAs, easements, and utility poles tell you which parts of that envelope you actually can't use. A 30-minute walk with a tape measure catches roughly 80% of the surprises before they become design problems.

The map check (5 minutes)

Pull SDCI's ECA map for your address. Note any of these on the parcel or within 50 feet of it:

• Steep slope — 40% or steeper, with at least 10 ft of vertical rise over no more than 25 ft horizontal. Carries a 15-ft buffer that follows it onto neighboring parcels.
• Landslide-prone, peat-settlement, or liquefaction zones. Common in West Seattle, Magnolia, Crown Hill, South Park, Georgetown, Duwamish, parts of Beacon Hill.
• Wetland, riparian, fish/wildlife habitat.

If any of these apply, you'll likely need a geotechnical report (step 1.3) and possibly an ECA review on the construction permit.

The lot walk (30 minutes)

Walk the property and note:

• Trees roughly 24 inches in diameter or larger (measured 4.5 ft above grade). Under Seattle's tree code (SMC 25.11), these are Tier 2 and generally can't come down. Their drip line is off-limits to construction.
• Trees overhanging from neighboring lots. Their drip line still constrains you.
• Slopes you'd describe as "steep" even if not formally an ECA.
• Fences vs. assumed property lines. Fences in Seattle are often two to three feet off the real line. Don't assume.
• Utility poles. Note their position and which way the service drop runs to your house.
• Visible easements. Shared driveway worn into the side line, manhole covers in the back yard, "future utility" markings.

What to hand to the architect

A simple sketch of the lot with:

• North arrow
• Approximate lot dimensions
• Main house position
• Every tree over ~12 inches with rough diameter
• Slopes and direction of fall
• Pole and service drop direction
• Any fence that's clearly not on the line

This becomes the input to the boundary survey decision (step 1.1) and the schematic design (step 2.2).