Medina ADU and detached ADU rules

Can I build an ADU or DADU in Medina?

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.

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.

On this page7 sections

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

How much room the property may have for an ADU

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 supplies the base yards, but temporary Ordinance 1059 changes side setbacks for six months from July 27, 2026 and sets a 90-foot minimum lot width across the residential zones. Lots from 15,001–20,000 square feet use 15 feet at the lower/first-floor portion and 20 feet above the first floor or 16 feet in height. On lots over 20,000 square feet, the lower side yard is generally 20 percent of lot width, between 15 and 20 feet, and the upper side yard is 25 percent, between 20 and 25 feet. Conforming ADU-eligible lots generally retain 30-foot front and rear yards. Reverify after January 2027 because permanent development-impact regulations remain pending.
FAR, lot coverage, or impervious area: Medina does not use a general residential FAR. Structural coverage varies by zone and lot size: typically about 25 percent on a conforming 16,000-square-foot R-16 lot and about 21 percent on typical conforming R-20, R-30, and SR-30 lots. Impervious coverage is generally 55 percent in R-16, 52.5 percent in R-20, and 50 percent on conforming R-30/SR-30 lots. The house, eaves, 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 · Medina Ordinance 1059: interim residential setbacks

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.

Obtain the City's parcel-specific critical-area/buffer and shoreline-jurisdiction determinations and confirm public sewer before design.
Confirm the zone, overlay, lot-area/width setback tier, height method, structural and impervious coverage, parking, trees, and legal-lot status.
Obtain Bellevue Utilities water and sewer capacity certification and resolve fire access, pressure, hydrant, and any sprinkler conditions.
Submit the Type 1 ADU registration and coordinated building, planning, site, tree, utility, and consultant documents.
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.
Temporary Ordinance 1059 changes side setbacks beginning July 27, 2026 and is nominally in force for six months; calculations must be effective-dated and rechecked after January 2027.
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 · Medina Ordinance 1059: interim residential setbacks

Address-level ADU feasibility

What to check before assuming a detached ADU will fit

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. Also do not design from the pre-July 27, 2026 side yards while temporary Ordinance 1059 is active. Check the current ADU chapter, the interim bulk ordinance, and any Ecology-approved shoreline amendments 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 Ordinance 1059: interim residential setbacksTemporary side-setback rules effective July 27, 2026 for six months while permanent development-impact regulations are considered.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.

What to check first

1
Confirm the parcel is inside Medina city limits and identify its current zone.
2
Map the principal home, lot lines, easements, trees, utilities, driveway, critical areas, and buffers on one current survey.
3
Test the ADU footprint against setbacks, height, floor-area or coverage limits, hardscape, parking, and construction access.
4
Ask the utility providers to confirm water, sewer, power, meter, side-sewer, and capacity requirements before fixing the design.
5
Have the city confirm the complete land-use, building, fire, right-of-way, tree, and utility permit list in writing.