Crushed Rock, Drain Rock and Soil Delivery in Bellevue, WA

Reworked Ground on a Slope

The USDA soil survey maps the center point of ZIP 98004 as Arents, Alderwood material, 6 to 15 percent slopes. Arents are soils that have been dug, moved and regraded, and here they are built from Alderwood material. The slope range in the name shows that the ground falls noticeably across the map unit.^[1]

Reworked soil varies from one spot to the next. A shovel may turn up gravelly loam, packed fill or pockets of softer material within a few feet of each other. Before building, dig a few test holes across the area to see what you are working with, and plan to remove anything soft or full of debris.^[1]

Sloped ground adds a second concern. Water flows across it rather than sitting still, and loose soil moves downhill with that water. Terraces, low walls and stone edges help hold a slope, and planting or mulching bare soil keeps it from washing out in a long rain.^[1]

The ground at the center point stands 220 feet above sea level.^[2]

A Damp Season at Sand Point

Bellevue's weather normals come from the NOAA station at Seattle Sand PT Wsfo, WA, about 5 miles from the center point. It averages 37.8 inches of precipitation a year, most of it as steady rain through fall, winter and spring rather than short summer bursts.^[3]

Snow is light but not unknown. The station averages 3.8 inches of snowfall a year, and it counts 25 days in a typical year when the low reaches 32 F or colder. A wet stone surface that freezes can loosen slightly, so a top layer with few fines that drains quickly holds up best.^[3]

At Sand Point the median last spring freeze falls on March 8, and the median first fall freeze on November 23. Plant tender perennials after early March, and top beds with mulch before late November.^[3]

Wet weather also limits when certain jobs go well. Compacting a base on soaked, muddy ground is hard, since water in the soil keeps it from packing tight. Late spring and summer, when the ground has dried out, give the best window for patio and drive work, while planting and mulching can carry on through the damp months.^[3]

Long stretches of damp weather let moss and algae grow on shaded stone. A crowned surface of clean crushed rock dries faster between rains than flat, fine-grained paths, and an occasional raking brings fresh stone to the top.^[3]

Drainage for Sloped Lots

On a hillside, water from higher lots arrives at the uphill edge of yours. A curtain drain catches it before it reaches a patio or a foundation: dig a trench across the slope, line it with fabric, lay a perforated pipe, and fill around it with Drain Rock. Lead the pipe to a storm connection or a safe outlet downhill.^[1],[3]

Downspouts need the same attention. Roof water dumped onto reworked soil on a slope can carve a gully or soak a retaining wall. A buried pipe bedded in #57 Crushed Stone, or a dry creek bed lined with River Rock, carries that water away in a controlled path.^[1]

Behind a retaining wall, a backfill of clean Drain Rock with a pipe at its base lets water escape instead of building up pressure behind the wall. That simple step keeps walls on sloped Bellevue lots standing straight through many wet winters.^[3]

Paths that run straight down a slope turn into small streams in heavy rain. A path that crosses the slope at an angle, or one with low stone steps and a short flat landing between them, slows that flow and keeps the gravel in place. Edging each step with timber or stone holds the surface where it belongs.^[1]

Building a Patio on Reworked Soil

Start by cutting a level pad into the slope and removing soft fill. Compact the exposed ground, then lay a woven geotextile. On the reworked Arents mapped at the center point, the fabric keeps mixed soil from working up into the base.^[1]

Lay Road Base or Crushed Concrete in thin lifts and compact each one until it is firm. Finish with a bed of Concrete Sand for pavers, or with 3/8" Crushed Stone or Decomposed Granite for a gravel patio. Slope the finished surface slightly away from the house so rain does not run toward the foundation.^[3]

Hold the downhill edge with a low wall, a timber or a row of large stone. On a slope, an unsupported edge lets the base creep downhill a little with each wet season.^[1]

Steps cut into a slope between a patio and the yard can use the same base. Pack Road Base behind each timber or stone riser, top the tread with 3/8" Crushed Stone, and tip each tread forward slightly so rain runs off rather than pooling against the riser.^[1]

Planting Beds and Small Yards

Reworked soil is often low in organic matter and may be compacted from construction. Fresh Topsoil gives lawns and beds a clean start, and Compost mixed into the top layer helps it hold air and water. Raised beds filled with Garden Soil work well on tight or sloped lots.^[1]

Mulch protects bed soil from the pounding of steady rain and keeps weeds down. Brown Shredded Mulch and Black Shredded Mulch knit together and stay on slopes, while Wood Chips suit paths and the ground beneath large trees.^[3]

For narrow side yards, a layer of Pea Gravel or Walkway Gravel over fabric gives a clean, dry path that drains quickly. Edge it so the stone stays put on a slope.^[1]

Tall evergreens drop needles that slowly acidify and clog a gravel surface. A light raking each fall keeps paths and drives clean. Under trees, a ring of Wood Chips instead of stone gives roots air and water, and it avoids the work of picking needles out of crushed rock.^[3]

Homes in ZIP 98004 and Across Bellevue

The Census counts 21,221 housing units in ZIP 98004. Detached houses make up 29 percent of them, owners live in 36 percent of the occupied homes, and the median home was built in 2001.^[4]

Bellevue as a whole counts 66,021 housing units, with 46 percent detached and a median year built of 1982. In the ZIP, newer townhomes and condos sit beside older houses on larger lots, so projects range from small courtyard refreshes to full drainage and patio rebuilds.^[4]

The Washington State Department of Transportation calls for Crushed Surfacing Base Course in Section 9-03.9(3) of its Standard Specifications for Road, Bridge, and Municipal Construction M 41-10 (2027). That compacted crushed layer gives state pavements a firm, draining foundation, which is the same goal for a home patio on sloped ground.^[5]