Reference

Washington Crawl Space Requirements

What the state requires of crawl space work, of the contractor doing it and of the paperwork that comes with it, for homeowners in King and south Snohomish counties. Each rule names the document that sets it and links to it. Written to be checkable, and useful whether or not you ever contact anyone through this site.

Sources drawn from 8 public bodies · last checked between August 20, 2026 and November 11, 2026

The Washington guides, in brief

  • L&I Contractor Lookup: How to Verify a Washington State Contractor License

    How to use L&I Verify for a Washington State contractor license search, and what the registration, bond, insurance and lawsuit sections of a record mean.

    • How to look a contractor up in the Department of Labor & Industries register, and what an active registration is: a registration, not a test of skill.
    • What the bond and insurance behind a registration cover, and that the bond is one sum shared by every claimant.
    • What recourse there is when a job goes wrong: a suit against the bond, with a deadline, and the Homeowner Recovery Fund after a judgment.

    Useful to Homeowners · Realtors · Property managers · Home inspectors

    30 primary sources: Washington State Department of Labor & Industries, Washington State Legislature, Washington State Department of Agriculture, Seattle Department of Construction and Inspections, City of Seattle, Office of City Finance

  • Washington Crawl Space Code

    What Washington’s residential code requires of a crawl space: the edition in force, the rules for vented and unvented crawl spaces, the radon and energy-code pieces, how Seattle’s code relates, and where the pending 2024 edition stands as of the last check.

    • Which edition is in force (the 2021 International Residential Code with Washington amendments, since March 15, 2024) and where the pending 2024 edition stands as of the last check.
    • What Section R408 requires of a vented crawl space and of a sealed one, including the radon system and the exhaust fan a sealed one needs.
    • The energy-code figures for floor and duct insulation, how Seattle’s code relates to the state’s, and what the code does not address.

    Useful to Home inspectors · Realtors · Contractors · Homeowners · Journalists

    13 primary sources: Washington State Building Code Council, Washington State Legislature, Seattle Department of Construction and Inspections, Washington State Legislature, Office of the Code Reviser

Washington rules covered elsewhere on this site

Key rules at a glance

21 rules that bear on crawl space work in the Seattle area, each in a few sentences, with the document it comes from and the date that document was last opened and checked. The rule is the summary; the source is the authority, and where the two ever differ the source governs. Sources for this table last checked between November 10, 2026 and November 11, 2026.

The code

The code: Washington rules with their sources
Topic The rule Written in
Edition in force Code page → The 2021 International Residential Code with Washington amendments, in force in every county and city since March 15, 2024. A 2024 edition is proposed and not adopted: the council put its final adoption on the agenda for October 30, 2026, the outcome of that vote is not confirmed, and no permanent rule had been filed when the status was last checked on November 11, 2026. WAC 51-51-003; WAC 51-51-008 WAC 51-51-003 — International Residential Code Washington State Building Code Council · checked WAC 51-51-008 — Implementation Washington State Building Code Council · checked Register filings affecting WAC 51-51-008 Washington State Legislature, Office of the Code Reviser · checked
Ground cover Code page → A ground cover of 6-mil black polyethylene, or an approved equal, must be laid over the ground in the crawl space, overlapped at least 6 inches at the joints and extended to the foundation wall. It may be left out where the crawl space has a concrete slab floor at least 2 inches thick. WAC 51-51-0408, R408.1 WAC 51-51-0408 — Section R408, Under-floor space Washington State Legislature · checked
Vent area Code page → The under-floor space must have ventilation openings through the foundation or exterior walls, with a net area of at least 1 square foot for each 300 square feet of under-floor area. Openings are placed to give cross ventilation, and one side of the building may have none. WAC 51-51-0408, R408.2 WAC 51-51-0408 — Section R408, Under-floor space Washington State Legislature · checked
Vent screens Code page → Vent openings must be covered for their full height and width with one of six listed materials, such as hardware cloth, cast-iron grating or corrosion-resistant wire mesh, and the least dimension of the covering’s openings may not exceed 1/4 inch. Operational louvers are permitted. WAC 51-51-0408, R408.2 WAC 51-51-0408 — Section R408, Under-floor space Washington State Legislature · checked
Closing most of the vents Code page → Vent area may be reduced to 1/1,500 of the under-floor area where the ground is covered with an approved Class I vapor retarder and the openings still give cross ventilation. If the installed ventilation is less than 1/300, or operable louvers are installed, a radon vent must be installed from a point between the ground cover and the soil, built to the radon appendix. WAC 51-51-0408, R408.2 exception WAC 51-51-0408 — Section R408, Under-floor space Washington State Legislature · checked
Sealed (unvented) crawl space Code page → Vents are not required where two numbered conditions are met. One: exposed earth is covered with a continuous Class I vapor retarder, its joints overlapped 6 inches and sealed or taped, its edges run at least 6 inches up the stem wall and attached and sealed to it, and a radon system meeting the radon appendix is installed. Two: continuously operated mechanical exhaust ventilation is provided at 1 cubic foot per minute for each 50 square feet of crawl space floor area, terminating to the exterior. There is an exception for under-floor plenums in existing structures. WAC 51-51-0408, R408.3 WAC 51-51-0408 — Section R408, Under-floor space Washington State Legislature · checked 2021 Seattle Residential Code, Chapter 4, Foundations Seattle Department of Construction and Inspections · checked
Radon Code page → The radon appendix applies in the seven counties the code lists as high radon potential (Clark, Ferry, Okanogan, Pend Oreille, Skamania, Spokane and Stevens), and to every building built with an unvented crawl space under R408.3, in any county. King and Snohomish counties are not in the table. In a listed county an unvented crawl space is not permitted at all. WAC 51-51-0332; WAC 51-51-60101 WAC 51-51-0332 — Section R332, Protection against radon Washington State Building Code Council · checked WAC 51-51-60101 — Appendix F, Radon control methods (AF101 and Table AF101(1)) Washington State Building Code Council · checked
Floor insulation, new work Code page → R-30 for floors, in new construction and additions. The table has one column for the whole state. Insulation squeezed into a cavity shallower than its label thickness counts at its compressed R-value. WAC 51-11R-40213, Table R402.1.3 WAC 51-11R-40213 — Table R402.1.3, Insulation minimum R-values and fenestration requirements by component Washington State Building Code Council · checked
Duct insulation Code page → Supply and return ducts outside conditioned space, which includes a vented crawl space, are insulated to at least R-8 where the duct is 3 inches in diameter or larger and R-6 where it is smaller. WAC 51-11R-40320, R403.3.1 WAC 51-11R-40320 — Section R403.3, Ducts Washington State Building Code Council · checked
Insulation in an existing house Code page → Altered parts of the building envelope meet the new-construction values, with exceptions where the building’s energy use is not increased: a floor cavity exposed during construction need only be filled with insulation, and nothing is required where the floor cavity is not exposed. WAC 51-11R-50300, R503.1.1 WAC 51-11R-50300 — Section R503, Alterations Washington State Building Code Council · checked
Existing houses Code page → Additions, alterations and repairs must meet the requirements for a new structure, without the existing structure having to comply with the code, and must not leave it less compliant than it was. Alterations that do not involve building a foundation, crawl space, slab or basement are not required to meet the radon section and appendix. WAC 51-51-0102, R102.7.1 WAC 51-51-0102 — Section R102, Applicability Washington State Building Code Council · checked

Contractors and contracts

Contractors and contracts: Washington rules with their sources
Topic The rule Written in
The contractor is registered with L&I, and the registration is active Verifying a contractor → Every contractor must register with the Department of Labor & Industries. It is a gross misdemeanor to advertise, offer to do work, submit a bid or perform work as a contractor without being registered, or while the registration is suspended or revoked, and to subcontract to or use an unregistered contractor. RCW 18.27.020(1), (2) RCW 18.27.020 — Registration required; prohibited acts; criminal penalty Washington State Legislature · checked
The bond: $30,000 general or $15,000 specialty, shared by every claimant Verifying a contractor → A registered contractor files a surety bond of $30,000 as a general contractor or $15,000 as a specialty contractor. The bond is conditioned on paying labor, state taxes and suppliers, and amounts adjudged against the contractor for breach of contract including improper work. It is one bond for all of the contractor’s work, the surety is not liable for more than its amount, and claimants other than residential homeowners may not be paid more than half of it. Cancellation of the bond automatically suspends the registration. RCW 18.27.040(1), (4), (5) RCW 18.27.040 — Bond or other security required; actions against Washington State Legislature · checked
Liability insurance on file with L&I Verifying a contractor → At registration and each renewal the contractor must furnish insurance, or an assigned account, of $50,000 for damage to property, $100,000 for injury to one person and $200,000 for injury to more than one person. Expiry or cancellation of the policy automatically suspends the registration. RCW 18.27.050(1), (2) RCW 18.27.050 — Insurance or financial responsibility required Washington State Legislature · checked
The NOTICE TO CUSTOMER disclosure statement, before work starts Bid checker → A contractor agreeing to repair, alter or construct four or fewer residential units must give the customer the statutory NOTICE TO CUSTOMER, in substantially the prescribed form, before starting work, once the bid or contract price totals $1,000 or more. The notice states the registration number, the amount of the bond or deposit and the date the registration expires. It warns that the bond might not be sufficient to cover a claim and is not for the customer’s exclusive use, that the customer may withhold a contractually defined percentage as retainage, that the property may be liened if a supplier, employee or subcontractor is not paid, and that the customer may ask for lien release documents. The customer signs it, and the contractor must keep the signed copy for at least three years. RCW 18.27.114(1), (2) RCW 18.27.114 — Disclosure statement required; prerequisite to lien claim Washington State Legislature · checked
No disclosure statement, no lien claim by that contractor Bid checker → A contractor subject to the disclosure requirement may not bring or maintain a lien claim under chapter 60.04 RCW based on the contract without alleging and proving that it gave the customer the disclosure statement. Failing to comply is also an infraction. RCW 18.27.114(4), (6) RCW 18.27.114 — Disclosure statement required; prerequisite to lien claim Washington State Legislature · checked
Two years to file suit against the bond Verifying a contractor → A claim against the bond is a lawsuit against the contractor and the bond in superior court. A residential homeowner’s action for breach of contract must be commenced by filing the summons and complaint within two years from the date the work was substantially completed or abandoned, whichever came first. Service is made on L&I, with three copies and a fee. The prevailing party in a residential homeowner’s breach-of-contract action on the bond is entitled to costs, interest and reasonable attorneys’ fees. RCW 18.27.040(3), (6) RCW 18.27.040 — Bond or other security required; actions against Washington State Legislature · checked
The Homeowner Recovery Fund, after a judgment Verifying a contractor → Beginning July 1, 2026, the owner of an owner-occupied single-family dwelling, or a multifamily dwelling of four or fewer units, may apply to L&I’s homeowner recovery program where they hold a final judgment against a registered contractor on a claim under RCW 18.27.040(3) for their primary residence, have proceeded against the bond, have not been paid in full, and apply within 90 days after the civil action concludes. Payment is limited to actual damages and may not exceed $25,000 per contractor per parcel. RCW 18.27.410 RCW 18.27.410 — Homeowner recovery program Washington State Legislature · checked

Permits and inspections

Permits and inspections: Washington rules with their sources
Topic The rule Written in
In Seattle: what the residential code exempts from a building permit Bid checker → Inside the City of Seattle a building permit is required to construct, alter or repair a building, and all work must meet the code even where no permit is required. No permit is required for minor repairs or alterations valued by the building official at $6,000 or less in any six-month period, provided no loadbearing support is removed, reduced, altered or relocated and ventilation is not reduced. Nor is one required, provided the building envelope is not changed, for listed minor work that includes insulating existing buildings, abatement of hazardous materials, and in-kind or similar replacement or repair of deteriorated members of a structure. Seattle Residential Code R105.1, R105.2 items 1 and 2 2021 Seattle Residential Code, Chapter 1, Administration Seattle Department of Construction and Inspections · checked
Electrical work in Seattle In Seattle an electrical permit is needed whenever wiring is installed, altered, extended or connected to equipment, which covers a new receptacle or circuit for a sump pump, a fan or a dehumidifier. An owner may do their own electrical work on a property they own and occupy; that is not an exemption from the permit. Seattle Department of Construction and Inspections, Electrical Permit Electrical Permit Seattle Department of Construction and Inspections · checked
Home inspections Inspection findings → A licensed home inspector enters and traverses a crawl space where it is readily and safely accessible, looks for signs of flooding and moisture penetration, and reports wood rot, pest-conducive conditions and a missing or inadequate vapor barrier on an earth floor. The inspector is not required to determine the cause of a condition, the method of repair or its cost, and need not enter where the access opening is smaller than 18 by 24 inches. WAC 308-408C-030, 308-408C-070, 308-408C-150 Chapter 308-408C WAC — Home inspectors: standards of practice Washington State Department of Licensing · checked

Code rules apply to new construction and to work that is being done. They do not by themselves require an existing house to be upgraded, and whether a particular repair has to meet them is decided by the local building department. The one permit rule in this table is the City of Seattle’s; no other city’s has been read, for the reason given in the backlog below.

What is not here, and why

A reference section is only as good as its honesty about its own edges. These topics were considered for this hub and are not published. Each says what is holding it back, so you know whether the gap is research, editorial priority, or a subject that cannot be answered accurately at all.

Permit Requirements for Crawl Space Work
Not publishable accurately for the whole area. There is no single authority: Seattle, each of the other cities this site covers, and King and Snohomish counties each amend their own permit chapter, and only Seattle’s has been read. Seattle’s rule is in the table above, and even there the chapter does not say how the department treats a ground cover, a sealed crawl space or a sump basin. A wrong permit answer costs real money, so this stays unwritten until each building department’s rule has been read.
Utility Rebates for Floor Insulation
Covered by the rebates guide in the resources section, which this hub links to instead of duplicating. Listed here so its absence from this section is not read as an oversight.

The standard applied here

  • Primary sources only. The body that sets the rule or holds the register, not a trade association’s summary of it, and not another company’s blog.
  • Editions and versions are named. Building codes and rebate schedules are revised. A citation that does not say which edition it read is not checkable.
  • Verification dates are real. When a page says a source was checked on a date, it means the document was opened on that date and still said what the page reports.
  • Limits are stated. Where something varies by city or could not be confirmed, the page says so instead of generalizing.
  • The agency’s text governs. Every summary here links the document it comes from. Where a summary and the agency’s current text disagree, the agency is right, and the corrections ledger is where the fix is recorded.

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