Adu Construction Spokane

An accessory dwelling unit is one of the highest-return projects a Spokane homeowner can build: a legal second home on your existing lot that can house aging parents, adult kids, a long-term renter, or simply a private guest suite. At the same time, ADU construction is one of the easiest projects to get badly wrong — undersized budgets, permits that stall for months, and contractors who disappear mid-build are all common complaints. Our approach to ADU construction in Spokane is built around two things: an itemized, line-by-item price before you sign anything, and a documented step-by-step process so you always know what phase your project is in and what happens next.

Whether you're calling it an accessory dwelling unit, a mother-in-law suite, a backyard cottage, or a carriage house, this page walks through what's actually involved in building one in Spokane — the types available, what drives the price, how permitting and zoning work locally, and how to vet a builder before you commit a deposit.

What Counts as an ADU?

"ADU" is an umbrella term that covers several very different construction projects, and the type you choose changes your budget, your timeline, and your permitting path more than almost any other decision you'll make.

• Detached ADU (backyard cottage): A freestanding structure built in the backyard, separate from the primary house, with its own foundation, roof, kitchen, bathroom, and utility connections. This is the most flexible option and what most people picture when they hear "backyard cottage," but it's also the most expensive per square foot since you're building an entire small home from the ground up.
• Attached ADU: An addition built onto the side or back of the existing house that functions as a self-contained unit with its own entrance, kitchen, and bathroom, while sharing at least one wall with the main structure. Attached units can save money on foundation and roofing work since you're extending existing systems rather than starting fresh.
• Garage conversion ADU: An existing detached garage is reframed, insulated, and finished out as a livable unit. Because the shell — foundation, walls, roof — already exists, this is usually the fastest and least expensive path to a legal ADU, though older garages often need foundation reinforcement, new electrical service, and added insulation to meet current energy code.
• Junior ADU (basement or interior conversion): A self-contained living space carved out of an existing basement or a portion of the main house, typically with a kitchenette rather than a full kitchen, sharing some systems with the primary residence. This is the lowest-cost route if you already have a basement with adequate ceiling height and egress potential.

Each of these is a legitimate ADU, and each one is a different construction project with a different price tag. Part of our first conversation with any homeowner is figuring out which type actually fits the lot, the budget, and the intended use — a rental unit for a college student has different requirements than a suite for an aging parent who needs single-level living.

Why Spokane Homeowners Are Adding ADUs

The reasons people build ADUs in this market tend to fall into a few consistent categories:

• Rental income: With steady rental demand near the universities and hospitals in the Spokane area, a detached cottage or garage conversion can generate monthly income that offsets a mortgage or funds other projects.
• Multigenerational living: Parents who want to stay close to family without living under the same roof, or adult children saving for their first home, are one of the most common drivers we see.
• Aging in place: A single-level backyard unit lets an aging parent maintain independence while family is nearby to help — this is especially common as a lower-maintenance alternative to a two-story home.
• Property value and long-term flexibility: A permitted, legal ADU adds usable square footage and rentable income potential to a property, which matters whether you plan to stay for decades or sell in a few years.

Whatever the motivation, the projects that go smoothly all start the same way: a clear-eyed look at what the lot can actually support, an honest budget conversation, and a written scope before a shovel goes in the ground.

What Our ADU Construction Service Includes

ADU construction isn't just framing and drywall — it's effectively building a complete small home, and every trade that goes into a full house build has to happen at a smaller scale. Our scope typically covers:

• Site evaluation, including lot layout, setback analysis, slope, tree removal needs, and utility access
• Design and layout planning sized to how the unit will actually be used (rental, in-law suite, home office with living space, etc.)
• Permit drawings and submission to the appropriate jurisdiction
• Excavation, foundation, and framing
• Roofing, siding, and exterior finishes that match or complement the primary residence
• Electrical, plumbing, and HVAC — including new utility connections or panel upgrades where required
• Kitchen and bathroom build-out, from cabinetry and countertops to fixtures and tile work, sized appropriately for a compact footprint
• Insulation and energy code compliance for a standalone, year-round living space
• Interior finishes: flooring, trim, paint, lighting
• Final inspections and closeout documentation

If your project is a garage conversion or basement JADU, several of these steps shrink considerably since the shell and some utilities already exist — which is part of why those paths cost less. We scope every project individually rather than quoting off a generic template, because a 400-square-foot studio cottage and a 900-square-foot two-bedroom detached unit are simply not the same job.

Our Documented ADU Build Process

One of the biggest sources of frustration on ADU projects is not knowing what's happening or when. We run every project through the same documented remodeling process we use on additions, kitchens, and full renovations, adapted for ground-up ADU construction.

1. Consultation and feasibility review

We walk the property, review your goals for the unit, and give you an honest read on what your lot can support — including rough setback and lot-coverage considerations that will affect placement and size.

2. Design and scope development

We develop a floor plan and exterior design sized to your budget and intended use, then translate that into a detailed, itemized scope of work — not a lump-sum estimate.

3. Permitting

We prepare and submit permit drawings to the jurisdiction your property falls under and manage the back-and-forth with plan reviewers. This is typically the longest and least predictable phase of an ADU project, and we build realistic buffer time into your schedule rather than promising a date we can't control.

4. Site work and foundation

Once permits are issued, we mobilize for excavation, utility trenching, and foundation work. For detached units this includes footings and a full foundation; for garage conversions, this phase may only involve foundation reinforcement or a new slab section.

5. Framing, roofing, and dry-in

The unit is framed, roofed, and wrapped to get the structure weathertight — an important milestone in a market where seasonal weather can affect exterior work.

6. Rough mechanicals

Electrical, plumbing, and HVAC rough-in happen before insulation and drywall, followed by inspection sign-off.

7. Insulation, drywall, and interior finish

Once mechanicals pass inspection, we insulate, hang and finish drywall, then move into cabinetry, countertops, flooring, trim, and paint.

8. Kitchen and bath install

Fixtures, appliances, cabinetry, and tile go in — the phase that turns a shell into a livable unit.

9. Final walkthrough and closeout

We complete a punch list with you, schedule final inspections, and hand over closeout documentation including warranty information and any permit certificates you'll need for insurance, financing, or future sale.

You get a written schedule at the start of the project and updates as each phase completes, so "when will this be done" never becomes a guessing game.

What Drives ADU Cost in Spokane

Cost per square foot is the number everyone asks about first, and it's also the number that's most misleading when quoted in isolation — a small, simple unit can cost more per square foot than a larger one because fixed costs like kitchen and bathroom build-out get spread across less area. Rather than hand you a single blended rate, we itemize every project so you can see exactly where the money goes. Our Spokane remodeling cost guide breaks down current pricing ranges by project type; for ADUs specifically, the biggest cost drivers are:

• ADU type: Detached new construction costs the most per square foot; garage conversions and basement JADUs cost the least because the shell and some utilities already exist.
• Size: Kitchens and bathrooms are the most expensive square footage in any home. A small unit still needs a full kitchen and bath, so cost per square foot drops as the unit gets larger and that fixed cost spreads out.
• Foundation and site conditions: Slope, tree removal, soil conditions, and distance from existing utility lines all affect excavation and utility-trenching costs.
• Utility connections: Whether the unit can tie into existing water, sewer, and electrical service or needs new service drops and possibly a panel upgrade makes a meaningful difference in the budget.
• Finish level: Stock cabinetry and laminate counters versus custom cabinetry and stone counters can shift the finish budget substantially — this is one of the easiest places to control cost without cutting corners on structure or mechanicals.
• Permitting and impact fees: Jurisdiction-specific permit and utility connection fees vary and should be quoted as a line item, not buried inside a general "permits" allowance.
• Access and site logistics: Backyard access for equipment, existing landscaping to protect or remove, and how far materials have to be carried all factor into labor time.

Every proposal we send breaks these categories out individually — foundation, framing, mechanicals, finishes, permits — instead of one lump number, so you can see what you're paying for and where there's room to adjust if you need to hit a specific budget. If financing is part of your plan, our financing options page outlines the ways homeowners typically fund a project this size, from home equity products to construction loans.

Permitting, Zoning, and Utilities

ADU rules are set at the jurisdiction level, and requirements differ depending on whether your property falls under Spokane city code or unincorporated Spokane County jurisdiction, along with any specific zoning on your parcel. Typical items a jurisdiction will review include:

• Setback distances from property lines for the new structure
• Maximum lot coverage and maximum ADU square footage relative to the primary residence
• Height limits for detached structures
• Parking requirements, if any
• Water and sewer capacity, or septic and well requirements for properties outside city sewer service
• Owner-occupancy rules, where applicable

Because these details are jurisdiction- and parcel-specific, we don't quote generic zoning numbers up front — we verify your property's actual requirements as part of the design phase and handle the permit submission directly, rather than leaving you to interpret code language on your own. If your lot has unusual constraints — a steep grade, an easement, a shared driveway, a septic system — we flag that in the feasibility review before you spend money on design.

Licensing, Insurance, and Our Lifetime Labor Warranty

An ADU is a full construction project — foundation to roof — and it should be treated with the same scrutiny you'd apply to hiring a builder for a new house, because that's effectively what it is. Before hiring anyone for a project this size, confirm:

• They hold an active Washington State contractor license and carry general liability insurance
• They carry workers' compensation coverage for their crew
• They'll put the scope of work, price, and payment schedule in writing before requesting a deposit
• They can explain how change orders are priced and approved before work starts, not after

We're a fully licensed and insured Washington contractor, and we back our work with a lifetime labor guarantee — if a workmanship issue shows up in the labor we performed, we come back and fix it. That's a standing commitment on every project we build, not just ADUs. You can review our credentials, coverage, and background in more detail on our licensing and credentials page.

Areas We Serve

We build ADUs, additions, and full remodels throughout the greater Spokane area, including Spokane proper, South Hill, and Spokane Valley, as well as surrounding communities including Deer Park, Mead, and Nine Mile Falls. Because permitting requirements and utility access vary by jurisdiction, let us know your specific location early — it directly affects both the permitting path and the site work portion of your budget.

Common ADU Mistakes to Avoid

We've seen the same handful of missteps derail ADU projects again and again. Watching for these up front saves real money and time:

• Designing before confirming what the lot allows. Falling in love with a floor plan before verifying setbacks, lot coverage, and utility access leads to expensive redesigns. Feasibility comes first, design second.
• Underbudgeting the kitchen and bathroom. These two rooms drive a disproportionate share of ADU cost. A budget that looks reasonable per square foot but skimps on kitchen/bath allowances usually isn't realistic.
• Ignoring utility capacity. Assuming the existing electrical panel or sewer line can simply absorb a second dwelling without checking capacity is a common and costly surprise mid-project.
• Choosing a builder on price alone. A quote that's dramatically lower than others usually means something is missing from the scope — permits, utility hookups, and finish allowances are the most common items left out to make a number look better than it is.
• Skipping the written schedule. Verbal timeline promises without a documented phase-by-phase schedule are the number one reason homeowners feel blindsided by delays.
• Not planning for how the unit will be used. A rental unit, an in-law suite, and a home office/guest suite have different layout, soundproofing, and accessibility needs — plan the layout around actual use, not a generic template.

How an ADU Fits Into a Larger Remodel

ADUs are often just one piece of a bigger property plan. Homeowners building a backyard cottage sometimes pair it with a kitchen or bathroom refresh in the main house, a deck connecting the two structures, or a garage build to replace parking space lost to the new unit. Because we handle the full range of remodeling work — from kitchens and bathrooms to additions, basements, and decks — we can plan an ADU alongside other work on your property so scheduling, permitting, and site logistics are coordinated rather than handled as disconnected projects. Start with our home page for an overview of everything we build, or dig into the cost guide and process page to see how ADU work compares to other project types before you commit to a scope.

Frequently Asked Questions

How big can an ADU be in Spokane?

Maximum size depends on your specific parcel, zoning, and jurisdiction — city versus county rules and lot size both play into it. We verify the actual limits for your property during the feasibility review rather than quoting a blanket number, since applying a citywide maximum to every lot leads to inaccurate expectations.

Do I need a permit to build an ADU?

Yes. ADUs require building permits and typically plumbing, electrical, and mechanical permits as well, since you're creating a fully independent living space. We prepare and submit all required permit drawings and manage the review process on your behalf.

Can I rent out my ADU?

Whether you can rent an ADU, and under what conditions, depends on your property's zoning and jurisdiction rules, including any owner-occupancy requirements that may apply. We recommend confirming your intended use with us early in the design phase so the unit is planned — and permitted — for how you actually intend to use it.

What's the difference between a garage conversion and a detached new-build ADU in terms of cost?

A garage conversion generally costs less because the foundation, walls, and roof already exist — you're primarily adding insulation, finishes, and mechanical systems. A detached new-build ADU starts from bare ground, so it includes full excavation, foundation, framing, and roofing costs on top of the same finish and mechanical scope. Our cost guide breaks out typical ranges for each approach.

How long does it take to build an ADU?

Timeline varies by ADU type and, significantly, by how long permitting takes in your jurisdiction — which is often the least predictable phase of the whole project. Garage conversions and JADUs move faster since less new structure is involved; detached new-construction units take longer. We provide a written phase-by-phase schedule once permits are secured so you have a realistic picture rather than a rough guess.

What financing options are available for an ADU?

Homeowners typically fund ADU construction through home equity loans or lines of credit, cash-out refinancing, or construction loans, depending on their existing equity and financial situation. Our financing options page walks through how these typically work so you can figure out which path fits your budget before design begins.

Ready to Talk Through Your ADU?

If you're considering a backyard cottage, garage conversion, or attached in-law suite anywhere in the Spokane area, the right first step is a feasibility review — not a design, and not a deposit. We'll walk your property, talk through what you're trying to accomplish, and give you an honest, itemized picture of what it will take before you commit to anything. Reach out to get that conversation started, and bring your questions about layout, budget, and timeline — that's exactly what the first visit is for.