Crawl Space Services in Seattle, WA

The nine crawl space services compared: what each one fixes, what it costs, which ones go together, and how to read the bids. Request a free in-home inspection and a written, no-obligation quote.

Free Inspection
A finished crawl space with a clean white reinforced liner across the soil, the walls sheeted to match and ductwork running overhead

Crawl space encapsulation, repair, and waterproofing across the Seattle metro, starting with a free in-home inspection and a no-obligation quote.

19 service areas covered
free inspections
Verify any contractor's registration: Washington L&I
Overview

What Crawl Space Repair Covers Around Seattle

"Crawl space repair" is one phrase covering a handful of very different jobs. Whatever happens in the gap between the soil and the floor framing under your house tends to get filed under this label, but it almost always comes down to three problems: moisture (encapsulation, vapor barriers, drainage, sump pumps), heat loss (insulation replacement), and what the moisture eventually grows or attracts (mold remediation, cleaning out what rodents leave behind).

Different homes in the area have different needs. A pre-war Seattle house with a dirt floor and old-growth joists is a different project from a 1980s Eastside house with sagging fiberglass batt and a torn plastic ground cover. The ground matters too. In Seattle a dense glacial till, known locally as hardpan, lies under the looser soils in many places, and the city's landslide study says water soaking down through them perches on top of it, drying up in spring or summer and returning in winter. An inspection of the actual conditions identifies the moisture source and the specific combination of services your home needs. Most homes need two or three of the nine services listed below, not all of them.

Scopes combine in predictable ways, and cold floors are a good illustration of why. Cold floors on their own sound like an insulation problem, but batt insulation rarely fails on its own; it falls because it got wet, or because animals nested in it. So the inspection that starts with cold floors often ends up looking at the condition of the vapor barrier, at whether the space needs cleaning out first, and at where any standing water is coming from, which may be as simple as a downspout emptying at the foundation or as involved as a perimeter drain. Fix the insulation alone and you have bought yourself the same failure again in a few winters. That is why a written line-item quote matters more than a single headline number.

Which crawl space repair comes first

Where a home needs more than one service, the water sets the order. Standing water or active seepage means drainage or waterproofing first, because a liner laid over a live water problem only hides it. Cleaning comes early too: debris, fallen insulation and rodent contamination come out before anything new goes in. Framing repair is scheduled with the moisture work rather than after it, so the new wood does not go into the crawl space that destroyed the old wood. The ground cover follows once the soil is no longer taking on water: a vapor barrier where the vents stay open, encapsulation where the crawl space is being sealed. Insulation is the last thing in, and mold remediation follows the same rule wherever it falls: remove the growth and correct what fed it, or it is back within months.

Worth knowing before you get quotes: floor insulation is the part of a crawl space project a utility may pay toward. Puget Sound Energy pays $2.50 per square foot, up to $5,000 in PSE-heated homes that meet its conditions, through a PSE trade ally who takes it off the invoice; Snohomish County PUD pays $1.00 per square foot in electrically heated homes it serves, through a PUD registered contractor; Seattle City Light lists no standard insulation rebate. Neither PSE nor the PUD lists the ground cover. Self-installed work does not qualify for the PSE rebate, so check eligibility before the work is scheduled; the 2026 rebate guide sets out each utility's conditions.

9 distinct services Most homes need two or three, not all of them.
10.55% Seattle sales tax Charged on the whole contract price; every range here is before it.
$3,400+ entry scope Vapor barrier, installed (modelled).
R408.3 Washington code section The clause that allows a sealed crawl space, and what one has to include.
All Crawl Space Services

The Nine Crawl Space Services

Each service has its own page with signs to watch for, process steps, what moves the price, and FAQs for homes around Seattle.

Pricing

What Crawl Space Repair Costs Around Seattle

Each service has its own range, and most homes combine two or three of them. These are the same 2026 modelled ranges the cost guide publishes, with the method behind them set out in full. All are before Washington sales tax, which is charged on the whole contract price at the rate for the job site. Cleaning and structural repair have no published range: what they involve cannot be known until someone has been under the house.

Service Typical Range What Pushes It to the High End
Vapor Barrier Installation Cost detail → $3,400–$4,675 Premium 20-mil cross-laminated barrier with wall coverage and double-sealed seams ($4,925–$6,725 total)
Crawl Space Drainage $4,025–$7,175 Complex hillside systems with multiple interceptors and long discharge runs ($7,625–$14,325)
Crawl Space Waterproofing Cost detail → $4,025–$7,175 Hillside lots with long discharge runs or significant existing flooding ($7,625–$10,650)
Sump Pump Installation Cost detail → $1,600–$3,125 Battery backup pump ($2,250–$4,025) or full drainage system with sump ($4,025–$7,175)
Crawl Space Encapsulation Cost detail → $10,650–$13,000 Dehumidifier, closed-cell rim joist foam, and full premium scope ($15,675–$21,500)
Insulation Replacement $2,500–$5,825 Spray foam on the foundation walls instead of the floor, which Washington’s energy code gives no crawl space wall path and PSE’s rebate does not cover ($4,025–$8,075)
Mold Remediation $1,600–$4,025 Full-area remediation paired with encapsulation or drainage to fix the source ($5,825–$10,650 combined)
Basement Waterproofing $7,625–$16,125 Dual sumps, large dehumidifiers, and finish replacement ($17,925–$26,875)
Foundation Waterproofing $15,825–$40,050 Hillside lots with shoring, deep excavation, or difficult access (beyond $40,050)

Modeled ranges for a 1,200 to 1,500 sq ft Seattle-metro crawl space in typical condition, before Washington sales tax.

Comparing bids

How to Compare Crawl Space Repair Bids

Choosing a contractor is covered on the home page for crawl space repair in Seattle, and how to verify a Washington contractor walks through the L&I lookup: anyone contracting for crawl space work in Washington has to be registered with L&I, bonded and insured. What follows is for the stage after that, when there are two or three written bids on the table.

Insist on a written, line-item scope

A crawl space bid should name what is being installed and how much of it: ground cover thickness and coverage, insulation R-value and square footage, drain length and sump model, exhaust fan or dehumidifier capacity, and what happens to the old material. A single lump-sum number cannot be compared with anything. The bid checker goes through a quote against what Washington requires a contractor to give you.

Ask what the evidence is

The most expensive disagreements between bids are about water. A drainage system and sump pump are the right answer for a crawl space with standing water and the wrong one for a dry crawl space with a torn barrier. A contractor recommending drainage should be able to show you the water, the tide line on the stem wall, or the photos from the wet season. The crawl space inspection guide lists the four questions that turn a pitch into a diagnosis.

Compare scopes, not headline prices

Two bids thousands of dollars apart are often quoting different jobs. Line them up item by item before deciding which contractor is expensive. Where one includes encapsulation and the other a barrier replacement, the question is which problem you actually have, not which crew is cheaper. Check too that both price the sales tax the same way; it is charged on the whole contract, and a bid that leaves it off is not lower.

Common Symptoms

Problems That Lead to Crawl Space Repair

If you recognize any of these in your home, the inspection will identify which combination of services solves it.

See all crawl space problems and what causes them

Process

How Crawl Space Repair Works

  1. Tell us about your crawlspace

    Answer a few questions about the house and what you are seeing. Takes less than 2 minutes.

  2. We follow up to schedule

    We get back to you by phone, text, or email to set a time for the inspection.

  3. Free in-home inspection

    The crawl space is checked for moisture, vapor barrier and insulation condition, drainage, and wood damage.

  4. Review a no-obligation quote

    You get a written scope and price. Compare it with our published cost ranges and approve only when you are ready.

Questions, Answered

Crawl Space Repair FAQs

Areas We Cover

King County

Snohomish County

All 19 service areas

Ready to Fix Your Crawlspace?

Request a free in-home crawl space inspection and a no-obligation quote for homes in the Seattle metro.

Free Inspection

Sources

Washington's R408 vent, ground cover and sealed crawl space rules and the radon county table cited in the FAQ; the EPA radon zone for King and Snohomish counties; the utility insulation rebates in the overview callout and the rebate FAQ; L&I's registration rule and contractor register; the hardpan and perched-water description from the Seattle Landslide Study; and the sales tax basis and Seattle rate.

  1. Washington State Legislature, WAC 51-51-0408 — Section R408, Under-floor space (Washington State Residential Code, amended by WSR 23-23-104) Checked

    What Washington requires under a house: ventilation at 1 square foot per 300 square feet of under-floor area; 6-mil black polyethylene ground cover with joints lapped 6 inches, extending to the foundation wall, which may be omitted where the crawl space has a concrete slab floor at least 2 inches thick; vent coverings with a least dimension of no more than 1/4 inch (corrosion-resistant wire mesh at 1/8 inch), and operational louvers permitted; ventilation reducible to 1/1,500 where a Class I vapor retarder covers the earth, with a radon vent built to Appendix AF required where ventilation is below 1/300 or operable louvers are installed. Vents may be omitted only where both numbered conditions of R408.3 are met: a continuous Class I vapor retarder lapped and sealed 6 inches, extending 6 inches up and sealed to the stem wall, with an Appendix AF radon system; and continuously operated mechanical exhaust at 1 cfm per 50 square feet. R408.8 is not adopted in Washington.

  2. Seattle Department of Construction and Inspections, 2021 Seattle Residential Code, Chapter 4, Foundations (Section R408, pages 4-47 and 4-48) Checked

    Two things. First, that Seattle’s R408.1, R408.2 and R408.3 carry the Washington-amendment marker and read the same as WAC 51-51-0408, apart from “Appendix F” where the state rule says “Appendix AF”; the copy shows the model code’s wording struck through, including its menu of alternatives for an unvented crawl space (dehumidification, conditioned supply air, perimeter-wall insulation), which is how the two numbered conditions of R408.3 are read as applying together. Second, the sections Washington does not amend, R408.4 to R408.6: an access opening not smaller than 18 by 24 inches through the floor or 16 by 24 inches through a perimeter wall; the under-floor grade cleared of vegetation and organic material, and forms and construction materials removed; and the under-floor grade as high as the outside finished grade where groundwater can rise to within 6 inches of the finished floor at the perimeter or surface water does not drain readily, unless an approved drainage system is provided.

    Note: The PDF marks additions by underline, which is lost when its text is extracted. “No Seattle-only change to R408” is drawn from the match with the state rule, not from a statement by the city. R408.4 to R408.6 are model code text and are summarised here, not reproduced.

  3. Washington State Building Code Council (via Washington State Legislature), WAC 51-51-0332 — Section R332, Protection against radon Checked

    Where the radon appendix applies. R332.1: to buildings constructed in the high radon potential (Zone 1) counties of Table AF101(1), and also to all buildings constructed using the unvented crawl space method of Section R408.3, in any county.

  4. Washington State Building Code Council (via Washington State Legislature), WAC 51-51-60101 — Appendix F, Radon control methods (AF101 and Table AF101(1)) (WSR 07-01-090, effective July 1, 2007) Checked

    The high radon potential counties and what follows from being one. Table AF101(1) lists seven Washington counties: Clark, Ferry, Okanogan, Pend Oreille, Skamania, Spokane and Stevens. King and Snohomish are not in the table. AF101.1: unvented crawl spaces are not permitted in any high radon potential county, and in other areas the appendix applies to any structure built with an unvented crawl space under R408.3.

  5. U.S. Environmental Protection Agency, EPA Map of Radon Zones — Washington Checked

    That King and Snohomish counties are in Zone 3, EPA’s lowest of three radon categories (predicted average indoor screening level below 2 pCi/L); Zone 2 is 2 to 4 pCi/L and Zone 1 is above 4. Washington’s Zone 1 counties are Clark, Skamania, Okanogan, Ferry, Stevens, Pend Oreille and Spokane. A low zone does not remove the Appendix AF radon vent that WAC 51-51-0408 requires where crawl space ventilation is reduced or the crawl space is built unvented.

    Note: EPA states the map must not be used to decide whether an individual home needs testing, and that every home should be tested regardless of zone. A county-level prediction says nothing about one building.

  6. Puget Sound Energy, Weatherization rebates Checked

    The PSE amounts and conditions this site quotes: floor insulation at $2.50 per square foot up to $5,000, in a site-built home built 1989 or before with 0 to 4 inches of existing insulation, finished to R-30 or a full joist cavity, where existing insulation may not be removed to qualify and the thermal boundary may not be moved; floor air sealing at $0.20 per square foot up to $400; duct sealing and insulation up to $1,000 per home, duct sealing only up to $550; that the customer must use PSE electricity or PSE natural gas as the primary source of space heating and live in a single-family home of four units or fewer or a manufactured home; that the work must be done by a PSE Recommended Energy Professional or Trade Ally, who takes the rebate off the invoice; that self-installed work does not qualify; and that the rebate cannot exceed the price of the work.

    Note: PSE states that this is a tariffed service that can change or end without notice, and the page gives no program year. The page lists no rebate for a ground cover, vapor barrier, dehumidifier or drainage. It still says a federal tax credit may be available; the IRS says that credit ended for work after December 31, 2025.

  7. Snohomish County Public Utility District No. 1, Weatherization Rebates Checked

    The Snohomish PUD amounts and conditions this site quotes: insulation at $1 per square foot for customers with electrically heated homes, where floor insulation must go from R-11 or less to R-30; duct sealing in a single-family home at $5 per linear foot up to $450; that the customer must own a single-family or manufactured home, or a townhouse or condominium in a building of up to four attached dwellings; and that the work must be done by a PUD registered contractor, who includes the rebate in the bill.

    Note: The page states no cap on the insulation rebate and no end date. It lists no rebate for a ground cover, vapor barrier or air sealing.

  8. Seattle City Light, Home Energy Solutions Checked

    That Seattle City Light’s residential page lists no standard rebate for insulation, air sealing or duct sealing: it advises sealing and insulating floors over crawl spaces, and sends insulation help to the income-qualified HomeWise program.

    Note: An absence read from one page on one day. City Light’s offers change; check the page before relying on this.

  9. Washington State Department of Labor & Industries, Register as a Contractor Checked

    That Washington requires every construction contractor to register with L&I and to be bonded and insured; that there are two classifications, general and specialty, with 63 specialties; that a specialty contractor works only in the registered specialty and cannot hire subcontractors; that plumbing, electrical, elevator, mobile home installation, boiler and asbestos work carry further education, examination and licensing requirements; the bond amounts ($30,000 general, $15,000 specialty); the liability insurance L&I asks for ($200,000 public liability and $50,000 property damage, or $250,000 combined single limit); that the bond and insurance must carry the exact business name; and that L&I suspends a registration when a bond or insurance policy lapses or a judgment goes unsatisfied.

    Note: L&I’s page for contractors. The statute states the insurance minimums differently (RCW 18.27.050); this site gives both.

  10. Washington State Department of Labor & Industries, Verify a Contractor, Tradesperson or Business Checked

    The official Washington register: registration status, bond, workers compensation account standing, and lawsuits filed against the bond.

  11. Seattle Public Utilities (prepared by Shannon & Wilson), Seattle Landslide Study, Volume 1 Checked

    That Vashon till, known locally as “hardpan”, is very dense and relatively impervious, so water soaking down through the deposits above it normally perches on top of it; that the contact between recessional outwash and till is normally less than 10 feet deep and the water perched there normally dries up in spring or summer and returns in winter; that the boundary where groundwater perches on the Lawton Clay is commonly termed “The Contact”; and that the study’s database holds 1,326 landslides reported through June 1999, records going back to 1890, about 84 percent with some human influence, landsliding in only about 1 percent of the city, and the highest densities in Southwest Magnolia, Southwest Queen Anne, Madrona, Interlaken and Alki.

    Note: The PDF prints no date; 2000 is the year Seattle Public Utilities gives for it. A 2003 update added about 110 landslides; this site quotes the original figures.

  12. Washington State Legislature, RCW 82.04.050 — “Sale at retail,” “retail sale” (Subsection (2)(b)) Checked

    That a retail sale in Washington includes the charge for labor and services in constructing, repairing, decorating or improving new or existing buildings for consumers, including installing or attaching tangible personal property. This is why sales tax applies to the price of crawl space work on a home, labor included.

    Note: The section was amended twice in 2026 and the Legislature’s page prints more than one version of it. Subsection (2)(b) reads the same in each version on the page.

  13. Washington Department of Revenue, Construction industry guide: Custom construction Explanatory summary, not the governing text Checked

    How the department applies the tax to construction for a landowner: the prime contractor collects retail sales tax on the gross contract price without deducting costs, the invoice must state the tax separately (a quoted price is presumed not to include it), and retail construction services are taxed at the combined rate for the location where the construction takes place.

    Note: The department’s guidance for contractors, not the statute. It cites RCW 82.08.050 for the separate-statement rule; this site has not read that section itself.

  14. Washington Department of Revenue, Local sales and use tax rate table (Quarter 4 2026, effective October 1 through December 31, 2026) Checked

    The combined state and local retail sales tax rate for each city this site covers, by Department of Revenue location code: from 9.9% in Everett to 10.7% in Lynnwood and Edmonds, and 10.55% in Seattle. The state rate is 6.5% on every row.

    Note: These rates apply from October 1 to December 31, 2026; the department republishes the table every quarter. Several cities have more than one location code, with a lower rate where the Regional Transit Authority tax does not apply or a different rate in a second county. The department’s address lookup (dor.wa.gov/TaxRateLookup) decides the rate for a specific house.

Sources last checked between and ; the date beside each one is when it was last opened. Where a figure comes from a document that is revised on a schedule, the edition or version is named above so you can confirm it against the current one yourself.