Des Moines Crawl Space Repair

Des Moines’ housing is concentrated between 1950 and 1989: 1,949 units from the 1950s, 2,586 from the 1960s, 2,125 from the 1970s and 2,182 from the 1980s, 70.6% of the city together. Before 1950 there are 823 units; since 1990, 2,863.

That spread means a Des Moines crawl space is usually somewhere between about 35 and 75 years old, and the right first question depends on where in that range it falls. Under a 1950s or 1960s house, start with whether there is any ground cover at all and how the framing nearest the soil has fared. Under a 1980s house, the original plastic and insulation are probably still there, and the question is how much of them is still doing its job: seams lapped, nothing torn by later work, batts still against the subfloor. Puget Sound Energy’s floor insulation rebate is limited to site-built homes built in 1989 or before, which on age alone takes in 77.1% of the city’s housing; the 2026 rebate guide lists PSE’s other conditions.

Most of Des Moines is one soil family. Alderwood gravelly sandy loams cover 54.1% of the mapped area across three slope classes, led by 32.1% on 8 to 15 percent slopes, and “Arents, Alderwood material” another 20.1%. The survey rates all of these moderately well drained, and there is no open water inside the mapped boundary at all. A good rating on Alderwood does not capture what the USGS describes underneath: hardpan that holds water in shallow wells through the winter, on till plains with poorly drained stream courses and closed depressions. So a crawl space that is damp only in the wet months is not contradicting the map.

The edges of the map are different. Alderwood and Kitsap soils mapped as very steep cover 6.0%, Alderwood on 15 to 30 percent slopes 4.4% and Kitsap silt loam on 15 to 30 percent slopes 1.2%, and 1.5% is mapped as coastal beaches. The state’s 1994 liquefaction map of the Des Moines and Renton quadrangles ranks Holocene beach deposits and fill high for liquefaction susceptibility, and the Washington Geological Survey’s lidar inventory of western King County found high landslide density along the Puget Sound bluffs. This site has not read whether either maps a particular Des Moines slope or lot.

On a sloping lot, where collected water goes matters as much as how it is collected: downhill is toward a neighbor or onto the slope. Ask the Building Division what applies to the parcel before anything is trenched, and make sure a drainage proposal names its discharge point. Where water arrives from uphill, a curtain drain is priced on this site’s cost guide at $2,250 to $5,375 on top of an interior drainage scope of $4,025 to $7,175, metro-wide and before tax. What crawl space drainage covers lists the parts.

The nearest published NOAA station to Des Moines’ Census internal point is Sea-Tac, 3.9 miles away, with a 1991–2020 annual normal of 39.34 inches. The Renton airport, 8.7 miles away, records 34.69 inches, and Tacoma #1, 10.7 miles away, 40.81 inches. The 6.12-inch spread among the three is modest and matches Federal Way’s. At Sea-Tac 75.4% of the year’s rain falls from October through March, on 93.4 days a year with a tenth of an inch or more.

Freezing nights are few: 25.2 a year at Sea-Tac and 27.2 at Tacoma #1, almost all from November to March. A crawl space here is shaped by six wet months more than by cold, so ventilation and ground cover matter more than heat tape, though water lines near the vents still deserve insulation. See high humidity in a crawl space for the moisture side.

Des Moines is almost all one ZIP code: 98198 covers 93.9% of the city, though 22.1% of that ZIP code’s land lies outside it. The other, 98148, covers only 5.8% of Des Moines and has about half its land in Burien. The city publishes no neighborhood list that this site found; its planning documents name an area called Pacific Ridge.

Inside the city, the Building Division of Community Development issues building permits, and building, electrical, plumbing and mechanical permits are all applied for online through MyPermits Online. Des Moines runs its own electrical permitting, and L&I lists it among the cities that do, so a circuit for a sump pump or dehumidifier is a city permit. This site has not read which crawl space work Des Moines exempts from a building permit, so ask the Building Division before assuming a scope needs none.

The Department of Revenue lists one rate, 10.4% for October 1 to December 31, 2026, on the whole contract price; the cost guide’s ranges are before it. King County’s Housing Repair Program, which lends to income-qualified owner-occupiers outside Seattle and Bellevue, covers Des Moines.