☐ Property is located within an Urban Growth Area (UGA)
☐ City or County jurisdiction over the UGA confirmed
☐ Zoning allows an ADU (Accessory Dwelling Unit) as an allowed use
☐ Local code allows two ADUs where applicable (attached and/or detached)
☐ No recorded covenants, easements, or deed restrictions prohibiting ADUs*
☐ Lot size, shape, and setbacks can physically accommodate the ADU footprint

* Work with a local Title Company, Surveyor, and Civil Engineer to confirm restrictions.

Common Early Red Flags

 ☐ GIS review completed for wetlands, streams, floodplains, and steep slopes
☐ Wetland or stream buffers identified and mapped as no-build zones
☐ Construction limits remain outside buffers (not just the building footprint)
☐ Civil Engineer establishes building envelope from construction limits
☐ Slopes verified under 33%, or geotechnical report planned
☐ Landslide setback compliance confirmed
☐ FEMA floodplain status checked (Monroe and river valley areas)

Higher-Risk Properties

 ☐ Sewer main location and depth verified
☐ Gravity sewer connection feasible to ADU location
☐ Grinder pump required (adds cost and review time)
☐ Existing side sewer condition verified
☐ Water meter size adequate for increased dwelling units*

* Preferred approach: individual water meters for each unit to reduce risk.

 ☐ Existing septic system bedroom capacity confirmed
☐ Reserve drainfield area identified
☐ Health Department clearance feasible
☐ Advanced treatment system required (ATU or mound system)

Common Project Killers

☐ Total new and replaced hard surface calculated

 ☐ Under 2,000 sq ft: Minimal drainage review
☐ 2,000–5,000 sq ft: Targeted Stormwater Site Plan required
☐ Over 5,000 sq ft: Full Drainage Report with modeling required

 ☐ Low Impact Development (LID) options evaluated
☐ Soil infiltration feasibility assessed
☐ Earthwork quantities estimated

 ☐ Less than 100 cubic yards of earthwork
☐ Over 100 cubic yards: Land Disturbing Activity (LDA) permit required

Cost Escalators

 ☐ ADU within required fire apparatus access distance
☐ Fire access road required or exemption confirmed
☐ Driveway width and load capacity compliant
☐ Required parking provided and code-compliant
☐ Parking does not encroach into setbacks or sight-distance triangles
☐ Gates meet emergency access standards where applicable

 ☐ ADU height limit confirmed for jurisdiction
☐ Height calculation method verified per municipality
☐ Rear yard, side yard, and front yard setbacks identified
☐ Tree retention impacts identified
☐ Washington State Energy Code (WSEC 2021) strategy selected
☐ Required number of energy credits confirmed

 ☐ High-efficiency mini-split heat pump planned (preferred system)
☐ Building envelope meets required R-value insulation standards
☐ Window and glazing performance compliant
☐ Small-unit energy credit compliance verified

 ☐ Topographic survey (2-foot contours)
☐ Engineered site plan
☐ Stormwater plan (Targeted or Full)
☐ Grading and erosion control plans (if required)
☐ Utility plan (water, sewer, power routing)
☐ Critical Area Site Plan (if applicable)
☐ Architectural floor plans and elevations
☐ Structural plans and calculations
☐ Energy code compliance forms
☐ Water availability letter
☐ Sewer availability letter
☐ PUD availability letter
☐ Address assignment request

 ☐ Building permit fees estimated
    (ADUs are often billed at ~50% of standard fees — verify with jurisdiction)
☐ Impact fees confirmed (school, park, traffic)
☐ Utility connection charges verified
☐ Public Works or right-of-way permit identified
☐ Four- to six-month permit review timeline assumed (best case)

* Expect multiple review cycles. Delays of 4–6 months are common due to response times.

 ☐ Sewer or septic capacity confirmed
☐ Critical areas manageable without variances
☐ Stormwater and grading triggers controlled
☐ Fire access feasible without major site work
☐ Fees and construction costs align with projected return

If all boxes are checked, the property is likely ADU-ready.
If not, this checklist may have prevented a major financial loss.

Recommendation:
Submit for a Pre-Application meeting first. Use written jurisdictional feedback as the roadmap for the full building permit submittal.

Accessory Dwelling Unit (ADU)
A secondary residential unit located on the same lot as a primary dwelling. May be attached or detached.

Detached Accessory Dwelling Unit (DADU)
An ADU that is a standalone structure separate from the primary residence.

Urban Growth Area (UGA)
A designated area where urban development is encouraged and public utilities are available.

Critical Area
Environmentally sensitive areas regulated by local code, including wetlands, streams, floodplains, and geologically hazardous areas.

Buffer
A required setback surrounding a critical area where development is limited or prohibited.

Critical Area Site Plan (CASP)
A legally recorded plan showing critical areas and buffer boundaries on a property.

Geotechnical Report
An engineering analysis of soil conditions, slope stability, and foundation requirements.

Gravity Sewer
A sewer system that relies on natural slope rather than mechanical pumping.

Grinder Pump
A mechanical pump used when gravity sewer flow is not feasible.

Side Sewer
The private sewer line connecting a structure to the public sewer main.

On-Site Septic System
A wastewater treatment system located on the property.

Reserve Drainfield
A designated area reserved for future septic system replacement or expansion.

Hard Surface
Impervious or semi-impervious surfaces such as roofs, driveways, patios, and walkways.

Targeted Stormwater Site Plan
A simplified drainage plan required when surface thresholds are exceeded.

Full Drainage Report
A comprehensive engineered stormwater analysis including modeling and facility sizing.

Low Impact Development (LID)
Stormwater strategies that mimic natural hydrology through infiltration and dispersion.

Land Disturbing Activity (LDA)
Grading or earthwork exceeding local permit thresholds.

Temporary Erosion and Sediment Control (TESC)
Construction-phase measures to prevent sediment runoff.

Fire Apparatus Access
A route meeting fire code requirements for emergency vehicle access.

Washington State Energy Code (WSEC)
State standards governing building energy efficiency.

Impact Fees
Fees charged to offset public infrastructure costs such as schools, parks, roads, and utilities.

Allowed Use
A land use that is permitted outright under zoning regulations without requiring a special exception or conditional use permit.

Attached ADU
An accessory dwelling unit that is physically connected to the primary residence (for example, above a garage or within an addition).

Best Case Timeline
An estimated review period assuming no major corrections, delays, or staffing backlogs at the reviewing jurisdiction.

Building Envelope
The area of a lot within which development is allowed after accounting for setbacks, buffers, easements, and construction limits.

Building Footprint
The portion of the lot covered by the structure itself, excluding decks, driveways, and other site features.

Building Permit
Formal approval issued by a jurisdiction allowing construction to begin once plans meet all applicable codes.

Civil Engineer
A licensed professional responsible for site layout, drainage, grading, utilities, and infrastructure design.

Construction Limits
The maximum area where any ground disturbance, grading, or construction activity is allowed on a site.

Conditional Use
A land use that may be allowed under zoning but requires additional public review or approval. (Note: ADUs are often not conditional uses.)

Covenants
Private, legally binding restrictions recorded on a property title that may limit development beyond local zoning rules.

Critical Area Ordinance (CAO)
Local regulations governing development near environmentally sensitive areas.

Detached Structure
A building that is completely separate from other structures on the lot.

Drainage Modeling
Computer-based analysis used to predict stormwater flow rates and verify system capacity.

Earthwork
Any grading, excavation, or fill activity on a site.

Easement
A legal right allowing a third party (such as a utility provider) to access or use part of a property.

Energy Credits
Points required under the Washington State Energy Code to demonstrate energy efficiency through approved strategies.

Engineered Plans
Plans prepared and stamped by a licensed professional engineer.

Environmental Review
A regulatory process evaluating the impacts of development on natural resources.

FEMA Floodplain
Areas mapped by the Federal Emergency Management Agency as having a risk of flooding.

Fire Code
Regulations governing emergency access, fire separation, and life safety requirements.

Fire Apparatus
Emergency response vehicles such as fire engines and ladder trucks.

Flag Lot
A parcel with a narrow access strip connecting the main portion of the lot to a public road.

Geologically Hazardous Area
Areas prone to landslides, erosion, or seismic instability.

GIS Review
Analysis using Geographic Information Systems to identify environmental constraints on a property.

Grading Permit
A permit required when earthwork exceeds local thresholds.

Gravity Flow
A system that relies on natural slope instead of mechanical pumping.

Height Calculation Method
The jurisdiction-specific formula used to measure building height, which may vary by slope or roof type.

Impervious Surface
Surfaces that prevent water from soaking into the ground.

Impact Fees
One-time fees assessed to fund public infrastructure needed to support new development.

Jurisdiction
The city or county authority responsible for reviewing and approving development.

Land Disturbing Activity (LDA) Permit
A permit required when grading exceeds a specified volume.

Load Capacity
The ability of a driveway or access route to support the weight of emergency vehicles.

Lot Coverage
The percentage of a lot occupied by structures or impervious surfaces.

Municipality
A city or town with its own land use and building authority.

No-Build Zone
Areas where construction is prohibited due to regulations or site constraints.

Permit Review Cycle
A round of comments issued by reviewers that must be addressed before approval.

Pre-Application Meeting (Pre-App)
An optional early review with the jurisdiction to identify issues before formal permit submittal.

Public Works Permit
Approval required for work affecting streets, sidewalks, or public infrastructure.

Reserve Area
Land set aside for future infrastructure needs, such as septic replacement.

Right-of-Way (ROW)
Public land used for streets, sidewalks, and utilities.

Setback
The minimum required distance between a structure and property lines or other features.

Sight-Distance Triangle
A required clear area at driveways or intersections to ensure visibility for vehicles.

Slope Percentage
A measurement of steepness calculated as vertical rise divided by horizontal run.

Stormwater Facilities
Infrastructure designed to manage runoff, such as pipes, tanks, or infiltration systems.

Surveyor
A licensed professional who measures property boundaries, elevations, and site features.

Targeted Review
A limited regulatory review triggered when specific thresholds are exceeded.

Title Company
A company that researches property ownership, liens, and recorded restrictions.

Utility Connection Charges
Fees required to connect new structures to public utilities.

Variance
Formal approval to deviate from code requirements. Variances significantly increase risk and timelines.

Written Jurisdictional Comments
Official feedback from reviewers outlining required corrections or conditions of approval.

If you want the PDF version of this checklist, it’s right down here.