600 1st Ave, Seattle, WA 98104

Office · Seattle · Seattle-Bellevue metro, WA

One of 1,701 reachable office buildings in Seattle. Larger than 83% of office buildings in Seattle (median 8,568 SF), derived from assessor records.

Usable building area
72,000 SF, King County Assessor
County gross area
89,355 SF, King County Assessor
Excluded area
17,355 SF outside primary usable area
Lot size
12,769 SF, King County Assessor
Year built
1900, King County Assessor
Stories
6, King County Assessor
Predominant use
Office Building, King County Assessor
Assessed value
$11,776,500, per the King County Assessor (not a market appraisal)
Assessed value per usable SF
$163.56/SF, derived from assessor records
Usable area / lot
5.64, derived from assessor records
Vintage
pre-war vintage
Zoning
PSM 100/100-130, King County
County use code
Office Building

Nearby comparable buildings

Same building type, by distance. Assessor facts only; not an opinion of value.

Want to talk to the owner? makeme1031 delivers a private letter directly to the owner of record. We never publish the owner's identity or address.

Own this building?

Claim privately

Claiming is for you. Your mailing address is never shown; no offer reaches you unless you opt in.

Claimed owners can confirm facts, watch the estimate, and decide whether to reply.

Received a letter about this building? It came from a real buyer through makeme1031; claiming is how you reply privately, on your terms.

Claimed owners also get Portfolio Pulse: a monthly email tracking this building's value.

Claim or manage this building

Sale history and market context

MakeMe Estimate: $12.3M (estimated market value), with a likely range of $10.5M to $14.4M (half of recent verified sales in this segment landed inside that range). Based on 7 verified arm's-length comparable sales (through 2026-06-01). Not an appraisal. How this estimate works.

lower confidence: 6 comparable sales within 3 miles; nearest 0.2 mi. This property type carries wider measured error; treat the estimate as a starting point. Comparable-sale caveat: the estimate is 40% below the $284.94/SF median of the shown comparable sales.

Comparable sales used as evidence

Recorded arm's-length sales of similar buildings nearby; nearer and more recent sales rank first. The strongest 5 of 6 nearby verified sales are shown. Buyer and seller names are withheld. Get this data via API.

Market context: Office in Seattle

median verified sale $364.58/SF over the trailing 24 months; 28 sales in the last 12 months and 52 in 24 (newest verified sale 2026-05); the middle 80% of recent sales traded at 0.63x to 1.44x their county assessed value, median 1.00x (52 sales with usable county values).

  • 2022: $472.22/SF median (35 sales)
  • 2023: $415.77/SF median (20 sales)
  • 2024: $326.92/SF median (24 sales)
  • 2025: $371.06/SF median (27 sales)
  • 2026 YTD: $390.03/SF median (11 sales)

This estimate sits at 1.05x county assessed value, the 54th percentile of those recent sale premiums.

Computed from 1,574 verified arm's-length sales in King County public records (52 in the trailing 24 months). Free public records. Not an appraisal.

Last sold: 2015-12-22 for $20,500,000 (recorded arm's-length sale).

Current ownership dates to 2015 (about 11 years) per recorded transfers.

Source: King County recorded sales extract; buyer and seller shown only when a company or organization. Individual names are withheld.

Value over time

$0$10M$20M$30M$40M201120142017202020232026$12.3MLast sold $20.5M · 2015$12.3M$11.8MCounty assessed valueMakeMe Estimate rangeRecorded sale

Dark line: county assessed value per King County tax rolls. Blue line: our estimate; dashed years are a modeled backcast built from recorded arm's-length sales in the building's segment, not estimates published at the time, and years without enough sales stay unmodeled. The shaded range is the model's measured error band; about half of verified sales in the segment land inside it. Diamonds: recorded arm's-length sales. Not an appraisal. How this estimate works.

Land, site, and value history

Assessed value moved from $7,222,000 (2011) to $11,776,500 (2026), up 63% over 15 years, per county tax rolls. The 2026 roll splits $11,776,500 into $5,746,000 land and $6,030,500 improvements.

Taxes

Permit history

Source: King County permit records (newest first).