BEBuild Eastside

Clyde Hill ADU and detached ADU rules

Clyde Hill ADU and DADU rules, including the critical-area stop sign

Clyde Hill allows two attached or detached ADUs, but it categorically prohibits an ADU on a lot containing a designated critical area or buffer. On an otherwise eligible lot, the normal R-1 setbacks, not the smaller ordinary accessory-structure rear yard, control a DADU.

Reviewed August 14, 2026 against adopted city code and official city guidance

Quick definitions. An accessory dwelling unit (ADU) is a complete additional home on the same property. A detached ADU (DADU) is in its own building. FAR or GFA limits how much enclosed floor area the property may contain.

Bottom line

What the current rules mean

An eligible lot may support up to two ADUs, each no larger than 1,000 square feet and 25 feet high. A detached unit generally needs the full 30-foot front and 35-foot rear yards plus the lot-area-based side yards. Before drawing anything, obtain the City's critical-area determination and Bellevue Utilities' water/sewer capacity certification.

Up to 2ADUs with one principal homeThey are not added on top of a middle-housing development.
1,000 sq ftMaximum per ADUThe 25-foot height cap also applies.
No ADUCritical-area or buffer lotThe code applies this as a parcel-wide eligibility screen.

What is allowed on one lot

Up to two attached or detached ADUs may accompany a single-family dwelling. Clyde Hill does not allow ADUs in addition to middle housing on the same lot.

  • Two attached or internal ADUs.
  • One attached and one detached ADU.
  • Two detached ADUs.
  • Conversion of an existing structure, including a qualifying nonconforming footprint, subject to size, parking replacement, building safety, and the parcel-wide critical-area rule.

Official sources: CHMC Chapter 17.39: accessory dwelling units · Clyde Hill official ADU guide · RCW 36.70A.681: limits on local ADU regulation

Size, height, setbacks, and site capacity

Maximum size
Each ADU is limited to 1,000 square feet.
Height
Each attached or detached ADU is limited to 25 feet under the ADU chapter, with Clyde Hill's grade and height-measurement rules still applying.
Setbacks
The normal R-1 yards apply; a DADU does not receive the smaller rear setback for ordinary accessory structures. Front is 30 feet and rear is 35 feet. Side yards are generally 15 feet each on lots of at least 15,000 square feet, 10 feet each above 10,000 but below 15,000, and 15 feet combined with a five-foot minimum on lots of 10,000 square feet or less. Upper-story setback planes can also apply. A qualifying alley lot line may use the state-authorized zero setback.
FAR, lot coverage, or impervious area
Structural coverage is 30 percent and impervious coverage is 60 percent. Clyde Hill does not use a separate base residential FAR, so the footprint, parking, walkways, utilities, and drainage must fit both coverage limits.

Official sources: CHMC Chapter 17.39: accessory dwelling units · CHMC Chapter 17.16: R-1 district

Parking, occupancy, renting, and separate sale

Parking
The current code requires two spaces per ADU on lots above 6,000 square feet, one per ADU below 6,000, and none within a half-mile walking distance of a major transit stop.
Owner occupancy
No owner-occupancy requirement applies. Long-term rental is allowed.
Short-term rental
Short-term rental is allowed only through Clyde Hill's annual business-license and safety program, including a local 24/7 representative, insurance, inspection/occupancy compliance, parking and traffic controls, and a prohibition on events.
Separate sale
The code includes a unit-lot-subdivision path that may support separate ownership. A condominium or unit-lot project requires approvals beyond the ADU registration and building permit.

Official sources: CHMC Chapter 17.39: accessory dwelling units · CHMC Chapter 5.20: short-term rentals

Utilities, fire access, and the permit path

The applicant must obtain Bellevue Utilities certification of adequate water and sewer capacity. Fire/building review, stormwater, address assignment, City registration, and a King County recorded covenant or registration document also apply.

  1. Request or confirm the City's critical-area/buffer determination before spending on an ADU design.
  2. Verify legal-lot status, R-1 setbacks and planes, structural/impervious coverage, address access, parking, and existing unit configuration.
  3. Obtain Bellevue Utilities water and sewer capacity certification and resolve fire-apparatus access, water supply, and any sprinkler mitigation.
  4. Submit the land-use/ADU and building package plus drainage, tree/landscape, utility, grading, and other site documents.
  5. Complete inspection, City registration, and the required King County recording before occupancy.

Official sources: CHMC Chapter 17.39: accessory dwelling units · CHMC Title 15: building and fire

Rules that can change the answer for one property

A citywide ADU allowance does not prove that a detached unit fits on a particular lot. Resolve these items before buying plans or fixing the DADU location.

  • Any designated critical area or buffer on the lot is a categorical local ADU blocker, even when the proposed footprint is elsewhere.
  • The City's general information suggests a different route for some nonconforming lots; state law may protect an ADU where the principal home is lawful, so get a written determination.
  • The smaller rear-yard allowance for an ordinary garage or accessory building does not apply to a DADU.
  • Bellevue utility capacity, long private access, hose distance, water pressure, and fire access can change cost or trigger sprinklers.
  • Upper-story setback planes, original grade, protected vegetation, views, drainage, and easements remain parcel-specific.

Official sources: CHMC Chapter 17.39: accessory dwelling units · CHMC Chapter 17.16: R-1 district

Prepared for a future address check

What a reliable DADU feasibility screen must verify

Clyde Hill's feasibility screen can be numeric only after a first, categorical critical-area/buffer test. If that test is clear, the engine can apply lot-area-based side yards, the 35-foot rear yard, 25-foot height, coverage, parking, and utilities.

Jurisdiction and zoning

Confirm the address is actually governed by Clyde Hill and select the correct base-zone standards.

Existing and proposed units

Count the principal dwelling, existing legal ADUs, middle-housing units, and the proposed attached or detached configuration.

Surveyed parcel geometry

Use legal lot lines, front/rear designation, alleys, access easements, and existing structures rather than a tax-map rectangle.

Capacity calculations

Test the ADU against the rules that apply locally: FAR or GFA, building or lot coverage, impervious or hard surface, and landscaping.

Mapped and field constraints

Screen critical areas and buffers, shorelines, slopes, flood hazards, significant trees, drainage, and recorded easements.

Utilities and emergency access

Verify water, sewer or septic, fire flow, hydrant and apparatus access, power, meters, and trench routes.

A public GIS layer is not enough to mark the critical-area test 'no.' The tool should require a formal or reliable City determination and should route uncertain mapping to manual review.

Primary sources

Official Clyde Hill and Washington references

These are the sources used for this guide. Check them again before filing because ordinances, fee schedules, and permit forms can change.

CHMC Chapter 17.39: accessory dwelling unitsCurrent count, configurations, size, height, eligibility, critical-area, registration, and recording rules.CHMC Chapter 17.16: R-1 districtCurrent front, rear, lot-area-based side yards, height planes, structural coverage, and impervious coverage.Clyde Hill official ADU guideCity application, utility, address, parking, and homeowner guidance.CHMC Chapter 5.20: short-term rentalsCurrent license, safety, representative, insurance, event, parking, and operating requirements.CHMC Title 15: building and fireAdopted construction and fire-access standards.RCW 36.70A.681: limits on local ADU regulationWashington's current baseline for two ADUs, size, height, parking, owner occupancy, conversions, alleys, fees, and critical-area exceptions.

A practical first-pass checklist

  1. 1

    Confirm the parcel is inside Clyde Hill city limits and identify its current zone.

  2. 2

    Map the principal home, lot lines, easements, trees, utilities, driveway, critical areas, and buffers on one current survey.

  3. 3

    Test the ADU footprint against setbacks, height, floor-area or coverage limits, hardscape, parking, and construction access.

  4. 4

    Ask the utility providers to confirm water, sewer, power, meter, side-sewer, and capacity requirements before fixing the design.

  5. 5

    Have the city confirm the complete land-use, building, fire, right-of-way, tree, and utility permit list in writing.