Renton ADU
City guide · permits · cost · zoning
Read guide →REGION_04 / SOUTH KING COUNTY
South King County
ADU builder.
South King County is the highest-yield ADU market in the region. Land basis is materially lower than Seattle or the Eastside while rents have caught up — especially on transit corridors and near major employment centers (Boeing Renton, Sea-Tac Airport, Valley Medical).
- Counties
- King County (South)
- Cities
- 8
- Best for
- Detached ADU (DADU)
- HQ
- Seattle, WA
Cities in South King County
SPEC_01 / COVERAGEBurien
Active coverage
SeaTac
Active coverage
Tukwila
Active coverage
Des Moines
Active coverage
Federal Way ADU
City guide · permits · cost · zoning
Read guide →Kent ADU
City guide · permits · cost · zoning
Read guide →Auburn ADU
City guide · permits · cost · zoning
Read guide →SPEC_02 / PERMITS
Permit complexity
Renton 8–12 weeks, Kent 10–14 weeks, Auburn 8–10 weeks, Federal Way 10–14 weeks. Airport-overlay (Part 77) review on SeaTac/Des Moines/Burien adds 2–4 weeks for height surface checks.
SPEC_03 / COST
Cost ranges
South King builds run 8–12% under Seattle averages — detached ADUs typically land $330–$370/sqft turnkey. Garage conversions on slab-on-grade homes are especially efficient in Kent and Auburn.
Full pricing breakdown →SPEC_04 / ROI
Rental ROI
Cash-on-cash yields are the strongest in the Puget Sound here. 600–900 sqft DADUs commonly rent $2,000–$2,800/mo against a much lower build basis, with strong demand from Boeing and warehouse-distribution workforce.
Run the ROI calculator →BEST FIT IN THIS REGION
Detached ADU (DADU)Garage conversionCash-flow rental ADUMulti-generational AADU
SPEC_05 / FAQ
South King County ADU questions
- Which South King city has the cleanest ADU permit path?
- Auburn and Renton both run 8–12 week timelines on clean submittals. Federal Way and Kent take a bit longer because of corridor-design and shoreline-buffer review on certain lots.
- Does the Sea-Tac Airport overlay affect ADU height?
- Yes — FAA Part 77 surfaces apply to SeaTac, parts of Des Moines, Burien and Tukwila. Most single-story DADUs stay clear, but two-story or attic-loft designs need a Form 7460-1 review.
- Are garage conversions a good move in Kent or Auburn?
- Often the best move. Both cities have lots of detached slab garages on flat lots with existing utility runs — converting to a 400–600 sqft ADU is meaningfully cheaper than ground-up detached construction.
- What's the rent ceiling on a South King ADU?
- Furnished 700–900 sqft DADUs near Boeing Renton or Valley Medical clear $2,800/mo regularly. Long-term unfurnished averages land $2,000–$2,500/mo, well above the cash-flow break-even.
OTHER PUGET SOUND REGIONS
FAQ
Frequently asked
Does Golden State serve South King County?
Yes — South King County is inside our active service area. We dispatch crews weekly to projects across South King County and maintain established relationships with each AHJ's plan reviewers, side-sewer departments, and inspection teams. The advantage of working with a regional builder is reviewer familiarity: when a South King County reviewer recognizes the contractor and the standard details, first-cycle approvals are dramatically more common.
What is unique about building ADUs in South King County?
Each South King County jurisdiction interprets WA statewide preemption (RCW 36.70A.681 / HB 1337) differently — height to peak vs midpoint, setbacks measured to siding vs eaves, drainage thresholds, side-sewer ownership rules. South King County cities also vary on fee structures and SDCs. Our South King County feasibility report names the exact code section, fee schedule version, and reviewer interpretation that will apply to your lot.
Go deeper: Read the ADU utility upgrades: sewer, water, and electrical service guide
How does South King County compare on ADU cost and timeline?
Construction labor and material cost is within ~6% across South King County jurisdictions because the same subcontractor pool services the region. Real cost variance is in fees (SDCs, capacity charges, school impact) and timeline (median 8–16 weeks permit, depending on AHJ workload). We publish per-city permit medians monthly so you can compare South King County cities directly before choosing a lot.
Go deeper: Read the Five hidden ADU costs that wreck Puget Sound budgets guide
Do I need a different contractor for each South King County city?
No — one license, one warranty, one point of contact across every South King County jurisdiction. Golden State holds an active WA general contractor license (GOLDESA747LZ) good statewide, plus relationships with L&I-licensed plumbing, electrical, and mechanical specialty contractors who work the full region. Using one regional builder for multiple South King County sites also helps when you want consistent rental specs across a small portfolio.
What's the typical permit timeline across South King County?
South King County medians from clean submittal in 2026: Seattle ~12–16 weeks, Bellevue ~10–14, Kirkland/Redmond ~8–12, Tacoma ~6–10, Olympia/Lacey ~6–10, Mukilteo/Lynnwood/Edmonds ~7–11. Catalog plans typically shave 2–4 weeks across every AHJ. Pre-application meetings shave another 4–6 weeks of total elapsed time. Outliers are almost always side-sewer issues, not building or planning review.
Go deeper: Read the King County side sewer permits for ADUs: cost & timeline (2026) guide
Are ADU rents different across South King County cities?
Yes, materially. South King County 1BR DADU rents in 2026 span $1,750/mo (Pierce County exurbs) to $3,200/mo (Eastside Bellevue/Kirkland/Redmond). The spread is driven by submarket fundamentals — proximity to transit corridors, employer concentration (Microsoft, Amazon, Boeing, UW), and school district. Our per-city rent comp pages update quarterly so pro-forma underwriting is current.
Go deeper: Read the ADU utility upgrades: sewer, water, and electrical service guide
Which South King County cities have the most favorable ADU rules?
Three South King County standouts for ADU friendliness in 2026: Kirkland (streamlined intake, low impact fees, fast addressing), Tacoma (low SDCs, generous lot-coverage allowance, 6–10 week median permit), and Olympia (low fees, knowledgeable reviewers, easy side-sewer process). Seattle and Bellevue have higher fees but the strongest rental yields. Trade-off is real — our compare pages model both for your specific underwriting.
Go deeper: Read the ADU utility upgrades: sewer, water, and electrical service guide
Can I scale a small portfolio across South King County?
Yes — many South King County investors stack 2–6 ADUs across King and Pierce for income diversification. Common pattern: 1–2 owner-occupied (with Section 121 implications), remainder rental. We sequence construction across the portfolio so labor crews flow efficiently and our internal estimating database keeps pricing tight. Portfolios benefit from consistent finish specs that simplify maintenance and tenant turn.
NAV_GRAPH / Local data
Build in the South King County
SOUTH KING COUNTY CITIES
INTERNAL_LINKS / Deep Map