The Stillaguamish sits on the north edge of town, and a lot of the yards along the valley floor are old river ground: fertile when it drains, and a slick gray clay when it does not. Winter rain piles up against houses that back toward the Centennial Trail and the river parks, and the lawn stays soft long after the street looks dry. Valley lots rarely need a tall wall. They do need the short wall, or the bed edge, to have a way for water to leave. A solid wall in clay becomes a dam.
Snohomish County · ZIP 98223 · 2020 population 19,847
Low walls, wet soil behind them
We drain the back of even a short wall. Clay loads up, freezes, and shoves. A wall with mortar-tight joints and no rock behind it tips in a few winters. The outlet for that drain is planned before the first course, because flat ground hides the fact that water has nowhere to go.
Most of these walls are garden and patio edges, two to three feet. We build them like they will be leaned on, because they will.
The ground in Arlington
Arlington is a valley town, not a hillside suburb. Lots near the farmland and the trail are often open to the west wind and sit on clay that holds water. After a wet week the soil smears under a boot and the moss moves into any thin spot in the grass. Houses closer to the river have a second problem: the ground is low, so a downspout that just dumps at the foundation has nowhere useful to send the water.
We plan work around that. Drainage goes in before we talk about a patio or a new lawn. Native plantings that actually belong on this floodplain — vine maple, salmonberry, and other understory that can take wet feet — do better than a plant list copied from a drier lot. Gravel paths and low rock work fit the rural edges of town without pretending the soil is something it is not.
How we do the work
A retaining wall is a structure. The part you see is the block, the boulder, or the timber. The part that keeps it standing is the base, the batter or the geogrid, and the drain rock behind it. We do not stack block on the sod and call it a wall.
Height decides everything. A low garden wall and a wall holding a drive are not the same detail, the same permit, or the same price. We measure the retained dirt, not the face you wish it were.
What we look at first
- Retained height, at the tallest point
- What is above the wall: a lawn, a drive, a house
- Water coming down the slope
- Access for block or for boulders
The base
Compacted rock, buried enough that the first course is not sitting in the organic layer. A wall is not a stack. If the base is soft, we dig out and replace it. There is no fabric or foam that fixes a bad base.
Drainage is part of the wall
Rock behind the face, a pipe at the heel, and an outlet you can see. Weep holes alone, stuffed with the native clay, are not a drain. This is the step that gets skipped on walls that lean.
Block, rock, or timber
Engineered block is predictable and what we use when the height or the permit wants an engineered system. Boulders fit the foothills and the older yards. Timber is a short-life choice in the wet, and we will say how many years you are buying.
More from this crew
- Retaining walls across Snohomish County
- Rock walls in Arlington
- French drain installation in Arlington
- Hardscaping in Arlington
- Patio installation in Arlington
- Retaining walls in Marysville
- Retaining walls in Granite Falls
- Retaining walls in Stanwood
Sources for the climate and the water
- USDA plant hardiness map for choosing plants that can take a Snohomish County winter.
- EPA WaterSense on watering less once a lawn or a new planting is established.
- EPA Soak Up the Rain on keeping roof and yard water from becoming someone else’s problem.
