Adu Builder Spokane

If you own a home in Spokane and you're weighing an accessory dwelling unit (ADU) — whether that's a detached backyard cottage, a garage conversion, a basement apartment, or an addition tucked over an existing garage — the builder you choose determines whether the project finishes on budget and on time, or turns into a permitting headache that drags through a Spokane winter. We build ADUs across Spokane with upfront, itemized pricing and a documented step-by-step process, built around two realities every Spokane homeowner runs into: this city's older housing stock, and Inland Northwest permitting and weather timelines that catch out-of-town builders off guard.

This page walks through what an ADU actually involves in Spokane, how our process works from first call to final inspection, what drives the cost per square foot, how to vet an ADU builder before you sign anything, and the questions we hear most from homeowners in South Hill, Spokane Valley, and the surrounding areas. If you're also considering other remodeling work alongside your ADU, our Spokane remodeling cost guide breaks down pricing across kitchens, baths, additions, and more.

What Counts as an ADU in Spokane

An accessory dwelling unit is a secondary, independently livable housing unit on the same lot as a primary residence. It has its own kitchen, bathroom, and sleeping area, and it can be rented out, used for aging parents or adult children, or held as a long-term investment. In Spokane, ADUs generally fall into four categories, and each has a different construction path, timeline, and cost profile:

• Detached ADU (DADU): A freestanding structure built in the backyard, separate from the main house. This is the most common request we get, especially on the larger lots common in South Hill and Spokane Valley.
• Attached ADU: An addition built onto the existing home, sharing at least one wall, with its own separate entrance, kitchen, and bath.
• Garage conversion ADU: An existing detached garage is converted into livable space. This is often the fastest and least expensive path because the foundation and shell already exist — though many Spokane garages built before the 1980s need new footings, upgraded framing, and new electrical service to meet current code.
• Basement conversion ADU: A below-grade unit built into an existing basement. This works well in Spokane's older two-story homes with tall basements, but it depends heavily on ceiling height, egress window requirements, and moisture control — all things we evaluate on the first site visit.

Each of these overlaps with other remodeling disciplines. A garage conversion is part garage construction, part electrical and plumbing rough-in. A basement ADU is fundamentally a basement remodel with a kitchen and a legal second entrance added. An attached ADU functions like a home addition with an interior separation wall. We treat every ADU project as its own trade discipline rather than a smaller version of a house build, because the code requirements — separate utility metering, fire separation, egress, off-street parking — are unique to accessory dwellings.

Why Spokane Homeowners Are Building ADUs Right Now

Three things are driving ADU demand across Spokane: housing costs that have pushed multigenerational living back into the mainstream, rental income potential in a tight rental market, and lot sizes in neighborhoods like South Hill that can physically accommodate a detached unit without crowding the primary home. We also see a steady stream of homeowners in Spokane Valley converting existing garages or shops into ADUs for aging parents who want to stay close but not share a kitchen.

Whatever the motivation, the build itself has to solve for the same three local realities: an older housing stock with foundations, wiring, and plumbing that weren't built to modern code; a permitting process that runs through the City of Spokane or Spokane County depending on where the lot sits; and a construction season shaped by winter freeze that limits site work, foundation pours, and exterior work to a narrower window than builders in milder climates are used to.

What Our ADU Construction Service Includes

We handle the full scope of an ADU build as a single, coordinated project rather than handing you off between subcontractors. That includes:

• Feasibility and site evaluation — reviewing your lot, setbacks, existing utility service, and any zoning constraints before you spend money on design.
• Design and permit drawings — floor plans, elevations, and structural details prepared to meet local code requirements for accessory dwellings.
• Permit submission and coordination — filing with the appropriate jurisdiction and managing the review and correction cycle.
• Site work and foundation — excavation, footings, and foundation appropriate to your soil conditions and frost depth.
• Framing, roofing, and building envelope — structural framing, sheathing, roofing, windows, and doors, sealed and insulated for Spokane's temperature swings.
• Mechanical, electrical, and plumbing — new or separated utility service, HVAC sized for the unit, and full kitchen and bath rough-in and finish.
• Interior and exterior finishes — flooring, cabinetry, countertops, paint, siding, and trim matched to your preferences and, where relevant, to the look of the primary residence.
• Final inspections and close-out — walking the unit with you, addressing punch-list items, and making sure certificate of occupancy paperwork is complete.

We give you an itemized proposal before construction starts, broken down by category — site work, foundation, framing, mechanical/electrical/plumbing, finishes, and permits — so you can see exactly where the money goes and where you have room to adjust scope if the budget needs to flex.

How the Process Works, Step by Step

Every ADU build follows the same documented sequence, which we detail in full on our Spokane remodeling process page. In short, here's what it looks like:

1. Initial consultation and site visit. We walk your property, look at existing structures if a conversion is on the table, and talk through your goals — rental income, multigenerational housing, or long-term equity.
2. Feasibility review. We confirm lot coverage, setbacks, parking requirements, and existing utility capacity before design work begins, so you're not designing a unit that can't legally be built where you want it.
3. Design and itemized proposal. You get floor plans and a line-item cost breakdown. This is the point where most homeowners refine scope — finishing level, square footage, roofline — against budget.
4. Permitting. We submit drawings to the correct jurisdiction and manage the review cycle, including any corrections. This is typically the longest single phase of an ADU project in Spokane and where an experienced local builder saves you the most time, because we know what each review office flags on first submission.
5. Site work and foundation. Excavation, footings, and foundation, scheduled around the ground being workable — we plan pours to avoid freeze windows whenever possible.
6. Framing and dry-in. Structural framing, roofing, windows, and doors go in to get the unit weathertight before winter weather can affect interior work.
7. Rough-in and inspections. Electrical, plumbing, and HVAC rough-in, each independently inspected before we close up walls.
8. Finishes. Drywall, flooring, cabinetry, countertops, fixtures, and paint, interior and exterior.
9. Final walkthrough and inspection. We walk the completed unit with you, resolve punch-list items, and coordinate final inspection sign-off.

We give you a written schedule at contract signing and update it at each phase, so you always know what's happening next and why — no guessing, no radio silence during permitting review.

Spokane-Specific Challenges We Plan For

Older Housing Stock

A large share of Spokane's housing was built well before current code, and that matters most on garage and basement conversions. Older garages frequently have undersized footings, no insulation, and electrical service that can't support a residential unit without an upgrade. Basements in older two-story homes may have adequate ceiling height for a bedroom but lack a compliant egress window, which means cutting a new window opening below grade — a job that has to account for the foundation type and drainage before it's cut. We evaluate these conditions during the feasibility phase, not after permits are already submitted, so surprises don't show up mid-construction.

Permitting Timelines

Where your lot sits determines who reviews your permit — the City of Spokane, Spokane County, or the City of Spokane Valley — and each office has its own review queue, submission format, and common correction items. ADU permitting is inherently more involved than a straightforward remodel permit because it typically requires separate utility connections, fire separation details between the ADU and any shared structure, and parking or setback verification. We build permitting time into your project schedule realistically from day one, rather than giving you an optimistic estimate that slips once the drawings are in review.

Climate and Construction Scheduling

Spokane's winter freeze affects foundation pours, exterior finish work, and site grading. We sequence projects so that site work and foundations happen when the ground is workable, and framing is prioritized to get the structure dried in — roofed, windows and doors installed — before the coldest months, so interior trades can keep working through winter regardless of weather. Insulation and building envelope details are also specified for our climate, not a generic national standard, since a backyard ADU with an under-insulated envelope is expensive to heat through an Inland Northwest winter.

ADU Construction Cost in Spokane

Cost is the question every homeowner leads with, and it's also the one that's hardest to answer with a single number, because detached, attached, garage-conversion, and basement ADUs have genuinely different cost structures. Here's how the major cost drivers break down:

Cost Per Square Foot

ADU construction cost per square foot in Spokane depends heavily on which type of unit you're building:

• Garage conversion ADUs tend to sit at the lower end per square foot, since the foundation, framing, and roof structure already exist. Cost is concentrated in insulation, new electrical and plumbing service, HVAC, and finishes.
• Basement conversion ADUs are similarly efficient on structure but can carry added cost if an egress window needs to be cut, waterproofing is required, or ceiling height needs adjustment.
• Detached new-construction ADUs run the highest per square foot, because you're paying for a full foundation, framing, roof, siding, and complete mechanical systems on a standalone structure — effectively a small home built from scratch.
• Attached ADUs generally land between garage conversions and full detached builds, since they can share some existing wall and roof structure but still require new foundation and full utility separation.

Finish level moves the number substantially within any of these categories — a builder-grade finish and a high-end finish on the same footprint can be very different budgets. We walk through exact per-square-foot numbers for your specific project type and finish level during the proposal stage, and our remodeling cost guide for Spokane has broader benchmarking if you're comparing an ADU against other renovation options for your budget.

What Else Drives Cost Up or Down

• Utility separation. Running a separate electrical panel, water line, and sewer connection versus tying into the existing home's service is one of the bigger cost swings on a detached or attached ADU.
• Site access and grading. Backyard lots with tight access, slope, or mature landscaping that has to be worked around add labor and equipment cost.
• Existing structure condition. On a garage or basement conversion, foundation repair, framing upgrades, or moisture remediation found during demo can add scope — we flag likely issues during feasibility review so they're priced in up front, not discovered mid-project.
• Permitting and impact fees. Jurisdiction-specific fees and any required utility hookup charges are part of the itemized proposal, not an afterthought.
• Finish selections. Cabinetry, countertops, flooring, and fixtures represent one of the widest ranges in the whole budget and are usually the easiest place to dial cost up or down without changing the footprint.

We don't give ballpark verbal estimates and adjust later — every proposal is itemized by category so you can see exactly what's driving the total, and where there's room to modify scope if you need to hit a specific number.

How to Choose an ADU Builder in Spokane

An ADU is a bigger commitment than a kitchen or bath remodel — it's a standalone structure with its own foundation, systems, and permit file. A few things worth checking before you sign a contract:

• Licensing and insurance. Confirm the builder is a properly licensed, bonded, and insured general contractor in Washington State, and ask to see documentation rather than taking it on faith.
• Itemized proposals, not lump-sum guesses. A builder who can't break down cost by category — site work, foundation, framing, MEP, finishes — hasn't actually scoped your project yet.
• A documented process and timeline. You should get a written schedule at contract signing, with clear phases and expected durations, not a vague "a few months" answer.
• Local permitting experience. A builder who regularly submits ADU permits in Spokane, Spokane County, and Spokane Valley knows what each office flags and can plan your timeline realistically instead of guessing.
• A workmanship warranty. We back our construction with a lifetime labor guarantee, which means if a workmanship issue shows up in your ADU down the road, we stand behind the work — not just for the first year, but for as long as you own the home.
• References and completed work. Ask to see other ADU or remodeling projects the builder has completed, and talk to homeowners about how communication and scheduling actually went during construction, not just the finished result.

Beyond ADUs: Our Broader Remodeling Services in Spokane

Many homeowners planning an ADU are also considering other work on the primary residence at the same time — either to fund the ADU through a larger renovation loan, or because an ADU project surfaces other needs in the house. We handle the full range of remodeling work in-house, which means the same project management and itemized-pricing approach applies whether you're building an ADU or tackling something else on the property:

• Kitchen remodeling — full layout changes, cabinetry, countertops, and appliance upgrades.
• Bathroom remodeling — from fixture and finish updates to full gut-and-reconfigure projects.
• Basement remodeling — finishing unused basement space into livable square footage, whether or not it's being converted into an ADU.
• Home additions — expanding the primary home's footprint, structurally distinct from an ADU but often planned alongside one.
• Custom home building — ground-up construction for homeowners building new rather than renovating.
• Decks — outdoor living space that often gets added alongside a backyard ADU to tie the two structures together.
• Garage construction — new garage builds, separate from garage-to-ADU conversions.
• Commercial remodeling — tenant improvements and commercial space renovation for local business owners.

If your project spans more than one of these — say, a garage conversion ADU plus a deck connecting it to the main house — we scope and schedule it as one coordinated project rather than treating each piece separately.

Common Mistakes Homeowners Make When Building an ADU

• Designing before confirming feasibility. Paying for full design drawings before confirming setbacks, lot coverage, and utility capacity can mean redesign costs if the plan doesn't fit the lot as drawn.
• Underestimating permitting time. ADU permits typically take longer than a standard remodel permit because of utility separation and fire separation review. Homeowners who budget the same timeline as a kitchen remodel are often disappointed.
• Ignoring existing structure condition on conversions. Assuming an old garage or basement is "basically ready" without a proper structural and moisture evaluation leads to change orders once demo starts.
• Choosing the lowest bid without an itemized breakdown. A lump-sum number with no category detail makes it impossible to tell whether corners are being cut on foundation, insulation, or utility work to hit a low price.
• Not planning for winter in the schedule. Starting site work or foundation pours too late in the season can push a project's dry-in date past the point where framing and roofing can proceed efficiently.
• Skipping the rental/use plan before design. Whether the unit is for a renter, a family member, or resale value changes decisions on layout, parking, and finish level — sorting this out before design saves a redesign later.

Warranty and Credentials

We stand behind every ADU we build with a lifetime labor guarantee — if a workmanship issue surfaces after the project is complete, we address it, for as long as you own the home. We're a licensed, bonded, and insured general contractor operating throughout the Spokane area, and every contract includes the itemized scope and written schedule referenced throughout this page, so there's a documented record of exactly what was agreed to and what was delivered. Homeowners who've worked with us can speak directly to how the process went from first consultation through final walkthrough — ask us for references specific to ADU and conversion projects when you reach out.

Service Areas

We build ADUs and handle full remodeling projects throughout Spokane and the surrounding communities, including South Hill, Spokane Valley, Deer Park, Mead, and Nine Mile Falls. Lot size, jurisdiction, and permitting requirements vary across these areas — a South Hill lot and a Nine Mile Falls property, for example, can fall under very different setback and septic or utility considerations — which is part of why the feasibility review happens before design on every project. See our full Spokane-area service coverage for details on where we build.

Frequently Asked Questions

Do I need a permit to build an ADU in Spokane?

Yes. Any accessory dwelling unit — detached, attached, garage conversion, or basement conversion — requires permitting through the jurisdiction your property falls under, whether that's the City of Spokane, Spokane County, or the City of Spokane Valley. This includes structural review, utility separation, and fire/life-safety requirements. We handle permit submission and the review process as part of every ADU contract.

How long does it take to build an ADU in Spokane?

Timeline depends heavily on ADU type and current permitting queues, but permitting is typically the longest single phase of the project — often longer than the actual construction. Garage and basement conversions generally move faster than new detached construction, since the foundation and structure already exist. We provide a written, phase-by-phase schedule at contract signing so you know what to expect for your specific project.

Can I convert my existing garage into an ADU?

In many cases, yes — garage conversions are one of the more cost-effective ADU paths because the foundation and shell already exist. The main variables are whether the existing footings and framing meet current structural code, whether the electrical service needs upgrading, and whether the garage has adequate insulation potential. We evaluate all of this during the site visit before recommending conversion versus new construction.

Can I use my basement as an ADU instead of building a separate structure?

Basement conversions can work well, particularly in Spokane's older two-story homes with taller basement ceilings. The main requirements are a compliant egress window or door, adequate ceiling height, and proper moisture control, plus a separate entrance from the main living space. We assess ceiling height, existing window openings, and foundation drainage before recommending this route.

What's the difference in cost between a detached ADU and a garage conversion?

A garage conversion is generally less expensive per square foot because the foundation, framing, and roof already exist — cost is concentrated in insulation, utilities, and finishes. A new detached ADU requires a full foundation, framing, roofing, and complete mechanical systems built from the ground up, which puts it at the higher end of the cost range. We provide an itemized cost comparison for your specific lot and goals during the proposal stage.

Will building an ADU affect my property taxes or need a separate utility account?

An ADU typically requires its own electrical service and, depending on the type, its own water and sewer connection, which is factored into the itemized proposal. Property tax impact is determined by the county assessor based on added square footage and improvements, not by us — we recommend confirming specifics with the assessor's office once your design is finalized, since we don't want to give you a number we can't stand behind.

Get an Itemized ADU Quote for Your Spokane Property

If you're ready to find out what an ADU actually costs on your specific lot — detached, attached, garage conversion, or basement — the next step is a site visit and feasibility review. We'll walk your property, talk through your goals, and give you an itemized proposal and written schedule before any construction begins. Visit our homepage to reach our team, or review our step-by-step remodeling process and Spokane cost guide to see how we approach pricing and scheduling before you commit to a project.