Gravel, Stone and Soil Delivery in Renton, WA

Gravelly loam over a dense layer

The USDA soil survey maps Alderwood gravelly sandy loam, 8 to 15 percent slopes, at the ZIP's center point. The Alderwood series makes up 85 percent of that map unit, so it is the soil that matters most for planning. Its top mineral layer is a gravelly sandy loam, a mix of sand, some silt and rounded pebbles that crumbles in the hand and lets water in at a fair pace.^[1]

About 35 inches down, the survey records densic material, a hard, compact layer that roots and water struggle to pass through. Rain soaks into the loose upper soil, reaches that dense layer and then spreads sideways along it. The survey rates the soil moderately well drained and places it in hydrologic group B, moderate infiltration. Put together, the profile takes in water readily at the surface and then holds a perched layer of it above the hard material after a long rain.^[1]

Shrink-swell in the top 100 cm is low, at 0.7 percent. The Alderwood soil barely moves as it wets and dries, which is good news for slabs, paver patios and retaining walls. Water moving through the soil is the thing to plan around on this ground.^[1]

Rain, cold nights and the airport gauge

Weather normals come from the NOAA station at Renton Muni AP, WA, about 3 miles away. It averages 34.7 inches of precipitation a year, enough to keep upper soils damp for long stretches and to test any drive or path that lacks a way to shed water.^[2]

The airport station counts 30 days a year with a low of 32 F or colder. A light freeze on a wet gravel surface can loosen the top stones, so compaction and a firm, well-drained base keep the drive from turning soft after a cold snap.^[2]

The median last spring freeze at Renton Muni AP falls on March 13. The median first fall freeze comes on November 16. Beds planted after the March date and mulched before the November date get the most from the growing season.^[2]

The ground at the center point stands 430 feet above sea level.^[3]

Moving water off a sloped lot

On an 8 to 15 percent slope with a dense layer below, water travels downhill underground as well as on the surface. A French drain cut across the slope above a patio or a house catches it. Dig a trench, line it with fabric, lay a perforated pipe on a bed of Drain Rock, and fill the trench to the top with more Drain Rock. Wrap the fabric over the stone before the final cover so silt stays out of the gaps.^[1]

For a driveway on gravelly sandy loam, clear the dark topsoil and roots, then compact the native ground. Fabric is optional on this coarse soil but helps where wet clay pockets show up. Build the base with Road Base or 1-1/2" Crushed Gravel in compacted lifts, and finish with 3/4" Crushed Stone or Driveway Gravel. With 34.7 inches of yearly precipitation at the station, a crown and a shallow ditch of #57 Crushed Stone along the low side keep the surface from rutting.^[1],[2]

A steep cut beside a drive may need armor. Riprap set along the toe of a bank breaks up fast water, and #4 Crushed Stone makes a coarse, free-draining backfill behind a block retaining wall.^[1]

Garden steps cut into a slope need a firm tread that will not wash out. Set timber or stone risers, pack each tread with Stone Dust Screenings or Decomposed Granite, and tamp it hard. The fine grit binds into a solid step that drains between storms, and it stays put through the cold nights that the airport station counts each winter, where loose stone on a slope would creep downhill one footstep at a time.^[1],[2]

Beds that drain on a wet slope

Gravelly sandy loam is a decent planting soil on its own, but the pebbles and fast top drainage leave it lean. Work Compost into the top layer, or build raised beds filled with Garden Soil so roots stay above the wet layer that can sit near the dense material after a storm. Topsoil spread over a lawn area before seeding evens out bumps and gives grass seed a finer bed than the native stony surface.^[1]

A thick layer of Brown Shredded Mulch or Wood Chips keeps rain from splashing soil out of beds and slows erosion on the slope. Black Shredded Mulch and Red Mulch work the same way with a different color. Around the foundation, a strip of River Rock or Pea Gravel over fabric keeps the wall dry and stops mulch from washing against the siding during a downpour. Paths of Walkway Gravel or Stone Dust Screenings drain fast and stay firm through cold, wet weeks.^[2]

Drain Rock or #57 Crushed Stone for a soggy yard

A wet patch in a lawn on this ground usually comes from water perched on the dense layer that the survey places at about 35 inches. Two stones solve most of these problems, and they are close cousins. Drain Rock is washed, roughly uniform stone with the fines rinsed off, so every gap stays open for water to move through. It is the right fill for a French drain, a dry well or the trench around a footing drain, where the whole point is to hold and pass water without clogging.^[1]

#57 Crushed Stone is angular crushed rock, about the size of a grape to a walnut, also mostly free of fines. Its sharp faces lock together better than round stone, so it handles foot traffic or a wheel load while still draining well. That makes it a good choice for a drainage path that people also walk on, the bed under a shed, or the ditch along a driveway edge. With 34.7 inches of precipitation a year at the Renton Muni AP station, a soggy area often needs both: a deep trench of Drain Rock to collect the water, and a top layer of #57 Crushed Stone where the trench crosses a path. Wrap either one in fabric where it touches the gravelly sandy loam, so fine soil does not wash into the stone and slowly fill the gaps that make it work.^[1],[2]

Homes in ZIP 98055

Census figures put 9,942 housing units in ZIP 98055. Renton as a whole counts 42,551 units.^[4]

Detached single-family houses make up 44 percent of homes in ZIP 98055. The citywide figure for Renton is 51 percent.^[4]

The median home in ZIP 98055 was built in 1990, against a Renton median of 1988. Owners occupy 55 percent of the occupied homes in the ZIP.^[4]

The Washington State Department of Transportation names its aggregate base standard Crushed Surfacing Base Course, Section 9-03.9(3), in its Standard Specifications for Road, Bridge, and Municipal Construction. The spec sets the grading for the layer under state pavement.^[5]

ZIP 98055 lies in King County, and Gravel Valet also delivers to Kent, Bellevue and Seattle.^[5]