Sammamish sits on a plateau above Lake Sammamish, and most of it was built out as subdivisions in the last thirty years. Under a thin layer of topsoil is glacial till, a hardpan that water barely soaks into, and many lots back onto tall stands of Douglas fir. A wall dug through a major root plate can kill the tree that is the reason you like the lot. We move the line or we shrink the wall.
King County · ZIP 98074
Walls under trees, without cutting the bank apart
Shade lots want a low stone or block edge to hold a bed, not a cut into the hill under the firs. We hand-dig when the machine would skin roots. Drainage still goes in. Leaf litter will clog a weep that sits at the surface, so the outlet is something we can find again.
Timber walls in permanent shade rot faster. We say that and we steer you to block or rock if the wall is meant to last.
The ground in Sammamish
The till is the reason so many yards here stay soggy in winter and dry out fast in summer. Water sits on top of the hardpan, so a new lawn or patio needs drainage planned in from the start. We put in French drains, grade the yard away from the house, and build patio bases deep enough that they do not heave.
Many neighborhoods have HOA rules for fences, front yards, and plant choices, and we work to those standards. Lots along the greenbelts get heavy shade and needle drop, so we use shade-tolerant planting and bark where grass has given up. Larger backyards here are a good fit for a full redesign: a paver patio, a low retaining wall to level the slope, and irrigation on a timer for the dry months.
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 the region
- Rock walls in Sammamish
- French drain installation in Sammamish
- Hardscaping in Sammamish
- Patio installation in Sammamish
- Retaining walls in Mercer Island
Sources for the climate and the water
- USDA plant hardiness map for choosing plants that can take a King 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.
