How to Plan for an ADU in Spokane: A Homeowner's Guide

June 13, 2025

As Spokane continues to grow, Accessory Dwelling Units (ADUs) offer a smart and flexible way for homeowners to maximize the value of their property. Whether you're looking to house aging parents, generate rental income, or simply increase your property's utility, ADUs are increasingly viable thanks to evolving local regulations. Here's a practical guide to help you understand what's allowed and how to plan your project successfully.

1. What Is an ADU and Why Build One?

An ADU is a self-contained secondary housing unit located on the same lot as a primary residence. It can be attached (like a basement apartment) or detached (like a backyard cottage). Spokane supports ADUs as part of its middle housing strategy, which aims to increase housing supply while maintaining neighborhood character.



Benefits include:

  • Housing for aging family members or adult children
  • Long-term or short-term rental income
  • Better use of existing infrastructure
  • Increased property value

2. Zoning and Location

ADUs are permitted in most Spokane residential zones, including RA, RSF, RSF-C, RTF, RMF, and RHD. Only one ADU is allowed per lot. If your property is in one of these zones and meets basic lot and setback requirements, you’re likely eligible.

3. ADU Types and Size Limits

Internal (Attached) ADUs

  • Must be within the existing home or attached to it
  • Max size: 800 sq ft or 50% of the main house footprint (whichever is smaller)
  • Must have at least an 800 sq ft primary dwelling (excluding garage)
  • Up to two bedrooms allowed

Detached ADUs

  • Located in a separate structure on the lot
  • Max size: 975 sq ft or 75% of the primary dwelling’s size, whichever is greater
  • Height limits: up to 16 ft, or up to 23 ft if built above a garage or accessory space
  • Total detached building coverage limited to 15% of the lot area

4. Setbacks and Placement

Front setback: Same as the primary house, or at least 6 ft behind it

Side and rear setbacks: Minimum 5 ft, but can be 0 ft if the rear faces an alley

ADUs must be within 150 ft of a fire access point (curb or street) unless sprinklered

5. Parking and Utilities

  • One additional off-street parking spot may be required (unless within 0.5 miles of transit)
  • ADUs must tie into existing municipal water, sewer, and electrical services

6. Occupancy and Short-Term Rentals

  • One of the two units (either ADU or main house) must be owner-occupied at least 6 months per year
  • Short-term rentals (like Airbnb) are allowed only if the other unit is the owner’s primary residence

7. Design Compatibility

ADUs must match the appearance of the main home:

  • Similar roof pitch, siding materials, and window styles
  • Designed to look secondary in scale and function

8. Building Code Requirements

  • Must comply with all local building, energy, plumbing, and fire codes
  • Attached ADUs require separate fire-rated walls and exits
  • Detached ADUs must meet structural and energy code requirements for new buildings

9. Step-by-Step: How to Get Started

Step 1: Check Your Zoning

Use Spokane’s zoning map or contact the Planning Department to confirm your property is eligible.

Step 2: Plan Your Design

Sketch out your ADU layout and measure setbacks. Choose attached or detached based on budget, site, and use-case.

Step 3: Apply for ADU Approval

Submit your ADU application with design plans. Spokane requires a deed restriction confirming owner occupancy.

Step 4: Record Deed Restriction

Record the form with Spokane County and send proof to the city.

Step 5: Get Your Permits

Apply for building, electrical, plumbing, and mechanical permits. Plan for inspections throughout construction.

Step 6: Build and Inspect

Hire a licensed contractor or do the work yourself (with permits). Pass all inspections and secure a final Certificate of Occupancy.

10. Helpful Resources

Final Thoughts

Adding an ADU to your property in Spokane, Washington is a smart way to future-proof your home and create flexibility. With the right planning and a clear understanding of local regulations, homeowners can add functional, attractive units that increase both livability and value.

If you'd like help evaluating your property or drafting a preliminary layout, feel free to reach out to our team at The Building Company. We specialize in helping Spokane, Washington homeowners navigate complex remodels, including ADUs, with ease and confidence.

A bathroom with teal tile walls, a white countertop, gold fixtures, and a mirror reflecting a wooden door.

Types of Showers: Which Style Is Right for Your Bathroom Remodel?

August 26, 2025
If you’re remodeling your bathroom, the shower isn’t just a utility — it’s one of the most important design and comfort decisions you’ll make.
Bright white kitchen with a large island, granite countertop, stainless steel appliances.

Do I Need Permits for My Remodel?

August 26, 2025
At The Building Company, we’ve guided hundreds of homeowners through this process across Spokane, Coeur d’Alene, and the surrounding areas.
Modern kitchen with white countertops, stainless steel hood, and vase of flowers.

How Do I Make Sure My Remodel Stays on Schedule?

August 19, 2025
A Spokane & North Idaho Homeowner’s Guide to Staying on Track (and Sane) During a Remodel Let’s be honest: remodels have a reputation for taking longer than expected. And in some cases, that reputation is well-earned. But it doesn’t have to be that way.
Modern kitchen with wood cabinets, stainless steel appliances, and a central island.

How Our Process Protects You During a Remodel — Even When Things Don’t Go as Planned

August 19, 2025
Why a Strong System Beats Hope Every Time Let’s be real: no matter how talented your builder is or how carefully you’ve planned, remodels are complex. Things don’t always go perfectly. Products show up late. Framing reveals surprises. Schedules shift.
Bright kitchen with white cabinets, granite island, stainless steel appliances, and pendant lights.

What Are the Different Types of Countertops — and How Much Do They Cost?

August 19, 2025
Choosing countertops is one of the biggest style and budget decisions you’ll make during a kitchen or bathroom remodel. And with so many options — from affordable laminates to high-end natural stone — it can be hard to know what’s worth it and what’s not.
Spacious entryway with dark wood floor, white paneled walls, and a chandelier.

Flooring Options for Your Remodel: What Spokane & North Idaho Homeowners Need to Know

August 19, 2025
When you’re remodeling your home, few choices impact the look, feel, and functionality of a space more than the flooring beneath your feet. At The Building Company, we walk Spokane and North Idaho homeowners through flooring options every day — helping them balance aesthetics, durability, budget, and lifestyle. Here's
Kitchen with dark cabinets, island, stainless steel appliances, and hardwood floors.

If They Use All Subcontractors, Why Do I Need a General Contractor?

August 19, 2025
One of the most common questions we get during initial remodel consultations is: “If a general contractor hires out all the work to subcontractors, can’t I just manage the project myself?”.
Modern kitchen with white cabinets, granite countertops, and an island with bar stools.

How Do I Phase a Remodel Over Time Without Wasting Money?

August 14, 2025
Not every remodeling project has to be all-or-nothing. In fact, many of our clients across Spokane, Coeur d’Alene, and North Idaho choose to remodel in phases — whether it’s due to budget, time, or life circumstances.
Two-story house with tan siding, brick accents, porch, and arched windows.

How Accurate Are Online Remodel Cost Estimators?

August 14, 2025
You’re thinking about remodeling your kitchen or adding a bathroom, and you punch a few numbers into an online cost estimator.
Houses covered in snow along a street under a cloudy winter sky.

What Should I Expect During the Design Phase of a Remodel?

August 13, 2025
When homeowners in Spokane or North Idaho start planning a remodel, one of the biggest surprises is how important — and detailed — the design phase really is. Before we swing a single hammer or order any materials, your project needs to be fully thought through on paper (or more likely, on a screen).