Landscaping a Small Sloped Backyard in Seattle: Retaining Walls, Drainage, and Usable Space

17 ft deep, 25+ ft wide, south-facing. First 8 ft level, then 3:1 slope (33%) down to fence. You've lost 10+ ft of usable yard. Deck permit denied (45% footprint limit). You want level space, planting, and drainage control in rainy Seattle.

Retaining Wall at the Fence: Yes, It's Doable

• No code barrier to building a wall at the property line—check setback rules.
• Need 3 ft working space behind wall = build 3 ft in from fence.
• Wall height: ~8 ft (your slope drop). Requires engineering, geogrid, drainage, permit.
• Bobcat access essential for backfill (gravel, not native clay).

Drainage Is the Real Project

• Upslope neighbors' water hits your wall. Must intercept before it saturates backfill.
• Perforated drain pipe at base of wall, wrapped in fabric, daylighted or tied to storm system.
• Swale at top of wall to catch sheet flow.
• Do not concentrate water onto neighbor's yard—liability risk.

Phased Approach If Budget Is Tight

1. Install drainage first (French drain along top of slope + wall base drain).
2. Terrace with 2–3 ft walls (easier DIY, less engineering).
3. Plant slope-stabilizing natives: sword fern, salal, Oregon grape, kinnikinnick.
4. Add patios/paths on terraces later.

Talk to a Seattle-area landscape contractor who does hillside work. This isn't a weekend project—it's structural.