Kent vs. Renton ADU rules
Both cities skip owner-occupancy and cap a typical ADU near 1,000 sq ft, so fees and speed are what differ. Kent exempts a first ADU from school, transportation, and park impact fees outright, with a second paying only 50% of the single-family rate (KCC 12.13.040(A)(10)). Renton's savings instead run through its PRADU pre-approved-plan program: waived plan-review fees, several impact fees waived or reduced, and permits that can issue in about a week — but only for one of its roughly eight PRADU plans. Kent also allows tighter siting, letting a rear-half DADU sit within 2 ft of the side and rear lines, versus Renton's 5-ft rear setback.
✓ Verified against code · August 19, 2026
Kent rules run under KCC 15.08.350 (Kent City Code), adopted by Ordinance 4517 (building on Ord 4464), in effect since July 30, 2025.
✓ Verified against code · August 19, 2026
Renton rules run under RMC 4-2-110C (Renton Municipal Code), adopted by Ordinance 6160 (amended by Ord 6173), in effect since June 16, 2025.
Rule by rule
| Rule | Kent | Renton |
|---|---|---|
| ADUs allowed per lot | Two ADUs per lot, in any mix — one attached plus one detached, two attached, or two detached. An ADU connected to the house only by a breezeway or shared roof (or attached to a garage) counts as detached.KCC 15.08.350(B)(1)–(2) | Two ADUs per legal lot as accessory to a principal dwelling — one attached plus one detached, two attached, or two detached. In the lower-density zones, the second ADU must meet the principal dwelling's location and setback standards.RMC 4-2-110C |
| Maximum size | 1,000 sq ft per ADU (no transferring square footage between the two). Excluded from the count: areas under 7-ft ceilings, up to 200 sq ft of covered decks and porches, and the host structure's floor area when the DADU is built within, above, or as an addition to an existing garage or accessory building.KCC 15.08.350(B)(6) | 1,000 sq ft of gross floor area and 1,000 sq ft of building area (GFA excludes garages, porches, exterior stairs; building area includes attached garages). Converting an entire single floor of the house may reach 1,250 sq ft.RMC 4-2-110C; 4-2-110I fns 40–41, 25 |
| Detached ADU height | 24 ft; chimneys, antennas, and railings may extend 4 ft above that.KCC 15.08.350(B)(4) | 24 ft to the highest ridge, with shed-roof averaging allowed. PRADU pre-approved plans are exempt from the height cap.RMC 4-2-110C; fns 23, 42 |
| Detached ADU setbacks | Zone setbacks apply generally — but a DADU in the rear half of the lot may come within 2 ft of the side and rear lot lines, and may sit on the lot line where it abuts a public alley (unless the alley is routinely plowed). The planning director may modify setbacks where lot shape makes an ADU infeasible.KCC 15.08.350(B)(3)(a)–(d) | Rear: 5 ft (zero at an alley; a DADU within 10 ft of the rear line must keep 25% of the rear yard's length clear). Side: 25 ft in RC/R-1, 5 ft in R-4 through R-8, 4 ft in R-10/R-14. A detached unit within 4 ft of another residential structure counts as attached.RMC 4-2-110C |
| Off-street parking | Zero within a half-mile walking distance of a major transit stop; one space per ADU beyond that, with director waivers available for special circumstances.KCC 15.05.040(A) parking chart (rev. 1/26) | One space per ADU — but zero within a half-mile walking distance of a major transit stop, and lots partially inside that walkshed count as entirely inside.RMC 4-2-110C; fn 20 |
| Owner-occupancy | None — the code affirmatively states an owner-occupancy covenant 'is not required,' and old recorded covenants can be released by the planning director (applicant pays the recording cost).KCC 15.08.350(B)(9) | None. The city confirms both units may be rentals — no on-site owner required.RMC 4-2-110C (absence); city HB 1337 page |
| Lot coverage / floor area | Underlying zone standards apply (maximum site coverage runs 30–55% by residential zone under the April 2026 charts). Note: ADUs count as dwelling units in Kent's density calculations.KCC 15.08.350(B)(8); 15.04.170 (Ord 4536) | Zone lot-coverage caps apply; detached accessory structures may exceed coverage by 5%. ADUs are excluded from density calculations. Structures existing before June 30, 2025 that convert to ADUs are exempt from coverage, setback, and size rules.RMC 4-2-110A; 4-2-110I fns 15, 17, 25 |
| Permit path & timeline | An ADU permit through Economic & Community Development plus the building permit; attached and internal ADUs in existing homes are exempt from residential design review. No published review timeline.KCC 15.08.350(B)(10); 15.04.180(10) | Permitted outright — building permit only, no discretionary land-use review. The city states PRADU pre-approved-plan permits can issue in about a week. No street improvements or sidewalks required.RMC 4-2-060; 4-2-080A.7; city PRADU materials |
Kent: worth knowing
- The first ADU is exempt from school, transportation, and park impact fees (treated as part of the single-family use); each subsequent ADU pays 50% of the single-family rate — all three verified in current code text.
- No metal, aluminum, or fiberglass siding on ADUs — an unusual materials rule.
- Separate ownership/condominiumization of ADUs is expressly allowed.
- Existing nonconforming structures — including garages violating setbacks — may be converted to ADUs.
- A shared water meter with the main house is permitted if a shared-meter notice is recorded with King County before permit issuance.
- The rear-half-of-lot 2-ft setback allowance is among the tightest DADU siting rules in the region.
Kent: on our watchlist
ReCode Kent Phases 2.5 and 3 are in progress (Phase 3 includes Mill Creek Historic District standards) — we re-check KCC 15.08.350 each pass while the package moves.
No published permit review timeline found; unverified.
Renton: worth knowing
- The PRADU (Permit Ready ADU) program offers roughly eight free pre-engineered plans (about 415–1,000 sq ft), with waived plan-review and application fees plus several impact fees waived outright and others reduced (some utility connection charges are cut ~30% rather than zeroed). City-estimated savings: around $40,000 — confirm current terms with Renton CED, since the waivers live in the fee schedule, not the code.
- PRADU plans are exempt from both the size cap and the height cap — that IS in the code.
- Renton amended its ADU code twice in 2025; content written between June and November 2025 may already be out of date on details.
Full detail: Kent · Renton · back to the Washington hub. Not legal advice — every fact above cites the code section it comes from; check the cite, or ask your city’s planning department to confirm your specific lot.