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Medina ADU and detached ADU rules

Medina ADU and DADU rules and the three parcel-wide exclusions

Medina allows two attached, internal, or detached ADUs, but it excludes any lot containing a critical area or buffer, any lot without public sewer, and any lot in shoreline jurisdiction. Those three threshold questions come before the normal size and setback analysis.

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 of 1,000 square feet each. A new DADU follows the lot-area and lot-width-based setbacks, a 25-foot-or-lower height cap, structural and impervious coverage, and cohesive site design. Get Bellevue Utilities capacity certification and clear the critical-area, shoreline, and sewer exclusions first.

Up to 2ADUs with one principal homeThey are not added to a duplex or two-unit middle-housing project.
1,000 sq ftMaximum per ADUThe roof height is capped at 25 feet or the lower principal-unit limit.
3 exclusionsCritical area, shoreline, sewerAny one can end the local ADU path before a fit test.

What is allowed on one lot

Up to two attached, internal, or detached ADUs may accompany one single-family dwelling when overall density and the ADU eligibility rules are met. They may not be added on top of a duplex or other two-unit middle-housing development.

  • Two attached or internal ADUs.
  • One attached and one detached ADU.
  • Two detached ADUs.
  • Conversion of a garage or accessory building, with replacement of displaced required parking and building-code compliance.

Official sources: MMC 16.34.020: accessory dwelling units · Medina Ordinance 1040 · 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
The maximum roof height is 25 feet or the lower height limit that applies to the principal dwelling. Medina's original-grade, finished-grade, low-point-plane, zone, and overlay rules determine the actual envelope.
Setbacks
The current residential table scales front and rear yards with lot area: generally 25 feet through 10,000 square feet, 26 feet from 10,001–13,000, 28 feet from 13,001–15,000, and 30 feet above 15,000. Side yards are generally 10 feet and can increase on lots over 20,000 square feet based on lot width. Overlays and current interim bulk rules must also be checked.
FAR, lot coverage, or impervious area
Medina does not use a general residential FAR. Structural coverage varies by zone and lot size, generally in the low-to-mid 20 percent range; impervious coverage is generally about 50–55 percent. The house, ADUs, garages, paving, pools, utilities, trees, and drainage must pass the applicable tables.

Official sources: MMC 16.34.020: accessory dwelling units · Medina residential dimensional standards

Parking, occupancy, renting, and separate sale

Parking
One additional space is required per ADU. Medina's local transit exception uses a quarter-mile radius, but state law requires no ADU parking within a half-mile walking distance of a major transit stop; apply the broader state exception and ask the City to confirm it for the parcel.
Owner occupancy
No owner-occupancy requirement applies.
Short-term rental
Short-term rental of an ADU is prohibited.
Separate sale
State law protects separate condominium conveyance from an ADU-only prohibition. Any unit-lot, condominium, or fee-simple division requires separate approvals and title work.

Official sources: MMC 16.34.020: accessory dwelling units · RCW 36.70A.681: limits on local ADU regulation

Utilities, fire access, and the permit path

Public sewer is mandatory, and Bellevue Utilities must certify adequate water and sewer capacity. A Type 1 ADU registration, building/site permits, and a King County recorded agreement are required before occupancy; cancellation also requires recording.

  1. Obtain the City's parcel-specific critical-area/buffer and shoreline-jurisdiction determinations and confirm public sewer before design.
  2. Confirm the zone, overlay, lot-area/width setback tier, height method, structural and impervious coverage, parking, trees, and legal-lot status.
  3. Obtain Bellevue Utilities water and sewer capacity certification and resolve fire access, pressure, hydrant, and any sprinkler conditions.
  4. Submit the Type 1 ADU registration and coordinated building, planning, site, tree, utility, and consultant documents.
  5. Complete inspections and record the required King County agreement before occupancy.

Official sources: MMC 16.34.020: accessory dwelling units · Medina permit application guidance · Medina master fee schedule

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.

  • No ADU is permitted under the local text on a lot containing a critical area or buffer.
  • No ADU is permitted in shoreline jurisdiction, even though older shoreline tables may appear to say otherwise; obtain a written current determination.
  • No ADU is permitted without public sewer, and Bellevue Utilities must certify water/sewer capacity.
  • A lawful buildable substandard lot may receive broader state protection than the local subdivision-related exclusions suggest; get a written determination.
  • Medina's lot-size/width setbacks, overlays, tree code, original-grade evidence, and structural/impervious tables can substantially shrink the envelope.

Official sources: MMC 16.34.020: accessory dwelling units · Medina residential dimensional standards

Prepared for a future address check

What a reliable DADU feasibility screen must verify

Medina's engine should begin with three categorical gates: critical area/buffer, shoreline, and public sewer. It can then apply current zone/overlay geometry, coverage, height, parking, trees, and Bellevue utility capacity.

Jurisdiction and zoning

Confirm the address is actually governed by Medina 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.

The screen must use the state half-mile parking rule rather than the narrower local quarter-mile text and should route any mapped critical-area, shoreline, substandard-lot, or utility uncertainty to written City confirmation.

Do not rely on the older rule

Some older shoreline-use material may look permissive, but the newer ADU section expressly excludes shoreline-jurisdiction lots. The current ADU chapter and any Ecology-approved shoreline amendments should be checked together before filing.

Primary sources

Official Medina 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.

MMC 16.34.020: accessory dwelling unitsCurrent count, configurations, size, height, parking, rental, design, exclusions, utility, registration, and recording rules.Medina Ordinance 1040The City's May 2025 middle-housing and ADU amendments.Medina residential dimensional standardsCurrent zone, lot-size and width setbacks, height, structural coverage, and impervious coverage.Medina permit application guidanceCurrent electronic application, submittal, review, and staff-contact information.Medina master fee scheduleCurrent ADU registration, permit, review, consultant, and related fee sources.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 Medina 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.