How We Produce the Cost Figures on This Site

The reference project

A price range is meaningless without the project it prices. Unless a page says otherwise, every “typical range” on this site describes this specific job:

• Size: 1,200 to 1,500 square feet of crawl space floor
• Condition: damp but without standing water at the time of the quote
• Access: a standard exterior or interior hatch with roughly 3 feet of working clearance
• Building: a single-family home on a continuous perimeter foundation
• Market: the Seattle metro (King County and south Snohomish County), priced in 2026 dollars before sales tax

Move any one of those and the number moves with it. The cost guide lists the specific adjustments — square footage, clearance, moisture level, insulation state — with the dollar amount each one adds in the model. The reference project is the one the Portland-metro model was written for. This site has not established that it is the typical Seattle-area crawl space.

How a range is produced

1. Define the scope. Each service is written down as a specific set of line items, which is why every service has a published included and excluded list. Most of the gap between two real quotes is scope, not margin.
2. Start from the Portland-metro model. This publisher’s Portland site carries an editorial estimate for each service and the reference project: a low and a high for the typical scope, and a separate premium band where a service has one. Those figures are judgements about a market. They were not built from a worksheet of quantities, hours and rates, and they do not rest on collected quotes, so they cannot be rebuilt from the ground up with Seattle inputs. They can only be adjusted.
3. Multiply by a published index. Every figure is multiplied by 1.05418. That is the 2024 all-items Regional Price Parity for the Seattle-Tacoma-Bellevue metropolitan area, 111.133, divided by the one for Portland-Vancouver-Hillsboro, 105.421. Both come from the Bureau of Economic Analysis, with the United States as 100.
4. Round to the nearest $25. The same step the Portland-metro table uses. The encapsulation range, for example, comes out at $10,650 to $13,000. The rounding is finer than the estimate is precise; read every figure as a band, not as a price to the dollar.
5. Leave sales tax out. The ranges are before tax, and the tax is listed with the other exclusions below.
6. Keep the table consistent. Add-ons, premium bands and the cost calculator’s dollar adjustments were scaled in the same pass by the same factor, and every page reads the same file, so a figure cannot be corrected in one place and left wrong in another.

How good is that index for this purpose

Not very, and it is used because it is published, checkable and not this site’s own invention. An all-items price parity measures what households pay for everything, rents included. It is a cost-of-living measure, not a construction cost index. The two metropolitan areas differ most on housing: the 2024 housing parity is 151.314 for Seattle against 125.114 for Portland, a ratio of 1.209. On goods they barely differ, and Seattle is slightly lower: 103.972 against 105.222, a ratio of 0.988. The 1.05418 used here sits between those.

One check on it is closer to the work. The Bureau of Labor Statistics reports a mean hourly wage for construction and extraction occupations of $42.11 in the Seattle metropolitan area and $39.44 in the Portland one for May 2025, a ratio of 1.068. Using that ratio instead would raise every figure here by about 1.3% before rounding. The two measures agree to within that margin, which is smaller than the width of any range in the table. Both metropolitan areas as the federal agencies draw them are wider than this site’s service area: the Seattle one includes Tacoma and Pierce County.

What would change these figures

• A revision to the Portland-metro model, which every figure here is a multiple of.
• New Regional Price Parities. The 2024 values were the newest published when these ranges were set.
• A decision to adjust by a construction-specific measure instead, which on the wage figures above would move every figure by about 1.3%.
• Collected quotes. If a service ever reaches the threshold set out below, its range would be replaced by one computed from them and labelled differently.

Any of those is recorded in the revision history with the date it was made.

What each range includes and excludes

This is the most useful part of the page when you are holding two quotes that differ by thousands. Read it as a checklist against the written scope in front of you.

Excluded from every range on this site

• Washington retail sales tax, which applies to the full contract price, labor and materials together, at the rate for the job site: 10.55% in Seattle from October 1 to December 31, 2026. Every range here is before tax
• Permit fees, which vary by jurisdiction and are usually billed at cost
• Structural repair of framing found to be rotten once the space is opened up
• Asbestos or lead abatement, which is separate work no range here prices
• Electrical service upgrades where an existing panel cannot carry new equipment
• Landscape or hardscape restoration after exterior excavation

Why sales tax is left out

In Washington, repairing or improving a building for its owner is a retail sale, labor included. The Department of Revenue’s guidance for contractors says the tax is collected on the gross contract price, that it must be stated separately on the invoice, and that construction is taxed at the combined rate for the place where the work is done. From October 1 to December 31, 2026 that rate is 10.55% in Seattle and runs from 9.9% to 10.7% across the cities this site covers; the department republishes its rates every quarter, and a few cities have more than one rate depending on the address.

So the ranges are quoted before tax for three reasons. A contractor’s bid shows the tax as its own line, and a before-tax range is the one that can be held against it. The rate depends on the address. And a range with a quarterly tax rate folded into it would go out of date every three months without any price having moved. The rate for each city is listed with the cost index.

Definitions

Several of these words are used loosely in the trade. Where this site uses one, it means this:

Typical range

The band this model puts on the reference project below in the Seattle metro. It is not a minimum, not a maximum, and not an average. A quote outside it is not thereby wrong.

Premium band

The higher band that applies when a project carries the specific complications named alongside it: hillside drainage, a dehumidifier, heavier materials, difficult access. It is a different scope, not a more expensive contractor.

Modeled estimate

A range produced by judgement and arithmetic rather than by measurement. Here it means an editorial estimate made for the Portland metro, multiplied by a published price index to move it to Seattle. Every range on this site is a modeled estimate.

Observed range

A range derived from a sample of real quotes. No range on this site is one. A service would need at least 30 quoted projects before this site would describe its pricing that way.

Before sales tax

How every range on this site is quoted. Washington retail sales tax is added to the full contract price at the rate for the address where the work is done, and is not in any figure here.

Data basis

The public classification each published figure carries: MEASURED, DERIVED, MODELED or OBSERVED QUOTE DATA. Every price on this site is MODELED. The four terms are defined in full, with what does and does not currently carry each, in the data section.

Encapsulation

Has no industry-standard definition, which is the single largest source of quote-to-quote variance in this trade. The scope priced here is a sealed liner on floor and walls with the vents and the access sealed; a dehumidifier is priced separately. Washington’s residential code, which governs new construction and permitted work, lists a radon system and continuous exhaust ventilation for an unvented crawl space, and neither is in the range. Two contractors can both honestly use the word for different work.

Class I vapor retarder

A code term, not a marketing one. Washington’s code asks for a ground cover of 6-mil black polyethylene or an approved equal in a vented crawl space, and names a continuous Class I vapor retarder, sealed at its joints and to the stem wall, for an unvented one. “Vapor barrier” in a quote is not automatically the same thing.

Limitations

What these figures cannot do, stated plainly so nobody has to infer it:

• These are modeled estimates, not measured data. This site does not hold a dataset of crawl space quotes for the Seattle market, and does not present one.
• They were not built for Seattle from the ground up. They are Portland-metro estimates moved here by one cost-of-living index, so anything that makes this market differ from Portland in a way that index does not capture is not in them.
• The Portland-metro figures underneath are themselves editorial estimates. Multiplying an estimate by a published number does not turn it into data.
• They price the reference project below. A 600 sq ft crawl space with 20 inches of clearance is a different job and a different number.
• They are before sales tax, which adds roughly a tenth to the bill in the cities this site covers.
• They are not a bid, an offer, or a price this site can hold anyone to. No contractor is bound by them.
• They are 2026 figures. They will drift with materials, labor and demand.
• They cannot account for what is not yet visible. Rot behind a barrier, a failed drain line, or contaminated soil are found during work, not during pricing.
• They are a yardstick, not a verdict. Written bids for your own house are better evidence, and the bid checker is there to compare them line by line.

If and when real quote data exists

The site takes inspection requests, so anonymised project data is a plausible thing to eventually hold. The reporting shape is fixed now, before any data exists, specifically so a thin sample cannot later be presented as a strong one:

• A service would need at least 30 quoted projects before its range could be described as observed.
• Any observed range would publish its sample size, median, and the date range the quotes were issued in — all three, or none.
• Services with real data and services without it would be labelled differently in the same table, rather than blending into one undifferentiated claim.
• Homeowner-identifying detail would never be published. A range and a count are not a project record.

Until every one of those conditions is met for a service, its figures stay labelled modeled.

Revision history

If you cited a figure from this site, this is where you check whether it has moved since. This log records changes to the ranges and to how they are produced, starting with how the first Seattle table was derived. Where a published statement turns out to be wrong rather than merely superseded, it is recorded separately and permanently in the corrections ledger, under the standard the editorial policy sets out.

1. November 10, 2026

   First Seattle table. Every range, premium band and add-on is this publisher’s Portland-metro editorial model multiplied by 1.05418, the ratio of the Bureau of Economic Analysis all-items Regional Price Parities for 2024 (Seattle-Tacoma-Bellevue 111.133 / Portland-Vancouver-Hillsboro 105.421), rounded to the nearest $25. All figures are before Washington retail sales tax. No contractor quotes were collected for the Seattle market, so every row is a modeled estimate. The index is a cost-of-living measure, not a construction cost index: using the ratio of construction and extraction wages in the same two metropolitan areas instead (1.068, Bureau of Labor Statistics, May 2025) would raise every figure by about 1.3% before rounding, and by no more than $525 on any row.

Citing this page

These figures may be quoted with attribution. Please name the review date alongside any figure, since the ranges are revised — “Seattle Crawlspace Pros, Crawl Space Cost Guide, reviewed November 10, 2026” — say that they are modeled estimates before sales tax, and link to the cost guide or to this page so a reader can see the methodology for themselves. If you are writing about Seattle crawl space costs and a figure here does not match what you are seeing in the market, that is worth knowing; tell us.

These ranges price an installation. What the same system costs to keep for ten or fifteen years — equipment replacements, filters, and maintenance this site found no published local rate for — is modeled separately, on the same footing and with its editorial allowances kept visibly apart from its published-range subtotal, in the encapsulation ownership-cost model.

For a suggested citation form, machine-readable CSV and JSON versions of these ranges, and the published field definitions, see the Seattle Crawlspace Cost Index in the data section.