Welcome to Your ADU Feasibility Roadmap
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Adding an accessory dwelling unit to your property is one of the most effective ways to create multigenerational housing or long-term rental value. However, before investing in construction drawings or hiring a builder, every successful project begins with one fundamental question: Is your property legally and physically buildable?
Understory provides complete, permit-ready architectural plan sets designed to meet fast-track permitting requirements in the Pacific Northwest. This self-paced guide is designed to walk you step-by-step through evaluating your parcel before you purchase a plan set or hire contractors
How This Guide Works
This guide functions as a self-paced directive. Review each of the four core buildability modules below, watch the brief video walkthroughs, and complete the checklist items for your lot:
Module 1: Zoning & Allowed Coverage — Confirm local municipal regulations, zoning allowances, and maximum lot coverage limits.
Module 2: Setbacks & Placement Envelopes — Measure required property line setbacks, power line clearances, and separation from your primary home.
Module 3: Critical Areas & Soils — Identify steep slopes, wetlands, erosion hazards, and triggers for site-specific engineering.
Module 4: Utilities & Access — Evaluate sewer or septic capacity, electrical panel room, and construction access constraints
Module 1: Zoning & Allowed Uses
Before falling in love with a specific floor plan or hiring a contractor, your first step is verifying what local municipal codes allow on your lot.
While accessory dwelling unit (ADU) regulations across Washington State and the Pacific Northwest have expanded significantly to encourage housing density, every city and county enforces specific limits on zoning designation, maximum lot coverage, and floor area ratios (FAR).
Follow these three steps to evaluate your parcel's zoning and footprint capacity.
Module 2: Setbacks
Once you know your parcel zoning permits an ADU and you have sufficient lot coverage capacity, your next step is identifying where on the property the building can actually sit.
A property may look wide open on a satellite view, but strict municipal zoning laws mandate minimum distances between your new structure and property lines, existing buildings, utility lines, and recorded easements. This unbuilt interior space is known as your buildable envelope.
Follow these three steps to map your property's placement envelope.
Module 3: How to Identify Critical Areas, Soils & Environmental Site Constraints
The Pacific Northwest is known for its lush tree canopies, hillsides, and coastal topography. While these natural features make for beautiful properties, they also mean local municipalities heavily regulate Environmentally Critical Areas (ECAs).
Building near a steep slope, wetland, stream, or protected tree canopy doesn't necessarily mean your property is unbuildable—but it does dictate where your DADU can sit and whether site-specific engineering or environmental reviews will be required prior to permitting.
Follow these three steps to evaluate your parcel's critical areas and soil conditions.
Module 4: How to Evaluate Utilities & Construction Access for an ADU
You’ve confirmed your zoning allows an ADU, mapped out your setback envelope, and verified your lot is clear of critical areas. The final technical hurdle before purchasing plans or breaking ground is evaluating utilities and site access.
Every detached accessory dwelling unit requires four core infrastructure connections: sewer (or septic), water, electricity, and power/data. Additionally, construction crews need a clear physical path to transport materials and machinery into your back yard.
Follow these three steps to evaluate your property's utility infrastructure and construction access.