What happens if you skip the permit (and you needed one)
- Stop-work orders and $500–$1,500 civil penalties per day; building enforcement may require demolition of unpermitted ADU, forcing you to rebuild to code at double cost.
- Title/insurance nightmare: unpermitted ADU voids homeowners coverage and creates a lien that kills refinance and resale — title company will flag it, lender will walk.
- Rental income tax exposure: if unpermitted ADU is discovered during audit or sale, you face back taxes plus 20% accuracy penalty on rental income claims.
- Neighbor complaint (common in Redmond's compact neighborhoods) triggers mandatory inspection; code officer has authority to issue citation and order cessation of occupancy within 30 days.
Redmond ADU permits — the key details
Washington State law (RCW 36.70B.140, effective January 1, 2023) is the spine of Redmond's ADU rules. The statute explicitly preempts local zoning and design standards — cities cannot ban ADUs, require owner-occupancy, mandate parking (in urban centers), or impose lot-size minimums beyond what applies to principal dwellings. Redmond's code (Chapter 21.76 ADR) acknowledges this preemption and allows one detached ADU or one attached junior ADU (interior second unit sharing walls) per single-family lot in all residential zones. Critically, the city does not require a separate lot, flag lot, or lot-split — you can add an ADU to an existing single-family parcel without subdividing. The permit path is a single building permit application (not a separate ADU permit), one fire/utility review, and one planning sign-off if the ADU triggers design or setback scrutiny. Most standard detached ADUs (800–1,200 square feet) qualify for over-the-counter approval if setbacks, egress, utilities, and parking (if required) are clear.
Egress and life-safety are the thorniest code hooks. IRC R310 and R311 require two independent exits from ADUs with sleeping rooms — one direct door to grade, one window (36 inches wide, 44 inches tall, sill ≤48 inches high, or egress well if basement). Redmond sits in Climate Zone 4C (Puget Sound) and 5B (east Redmond), both requiring frost protection at 12 inches minimum (some east Redmond sites need 30 inches for volcanic/glacial till soils). Slab-on-grade detached ADUs are typical, but if the ADU is elevated or has a crawlspace, foundation plans must show frost depth, drainage, and perimeter insulation per IRC R401.2. Garage conversions trigger extra scrutiny: the door between garage and ADU must be a self-closing, 20-minute fire-rated door with automatic closer (IBC 508.2.2). Utility separation is non-negotiable — the ADU must have its own electrical service or sub-meter, its own water/sewer stub (or point-of-use treatment if on well), and its own gas meter if applicable. The city will not sign off final utility without photographic evidence of separate service entrance.
Size and setback rules are state-capped but city-administered. Washington law allows junior ADUs up to 1,200 square feet or 25% of principal dwelling floor area (whichever is smaller), and detached ADUs up to 1,200 square feet on a lot under 7,500 square feet, with no size limit on larger lots. Redmond's setback requirements for detached ADUs match the principal dwelling: typically 15 feet front, 5 feet side, 20 feet rear in R-1 zones, varying by zone. The city uses a 'lot-line distance' measurement from exterior wall to property line — not from footprint. Junior ADUs (interior) require no additional setback beyond the principal dwelling. Parking is the variable cost — Redmond requires one off-street parking space per ADU in suburban zones (R-2, R-3), but waives the requirement in urban centers (Town Center, downtown Redmond, near transit hubs). If parking is required, a single space (9 feet × 18 feet) suffices; tandem is allowed. This waiver alone can save $15,000–$25,000 (cost of a paved space or variances in Puget Sound markets).
Utility and mechanical loads need early disclosure. A 1,000-square-foot detached ADU with a kitchen, two bathrooms, and electric heating can trigger sewer line upgrades (if the main line is undersized), water-main loops, and electrical service upsize (from 100A to 200A service). Redmond's utility department reviews all ADU applications; if the property is on municipal water/sewer, the city will run a capacity check and quote line-extension or looping costs (typically $2,000–$8,000). If on septic/well, a perc test and site evaluation are required (≤$1,500). HVAC loads must be modeled if the ADU is conditioned air; the city building inspector may request Manual J or ductwork calculations for code compliance. Wildfire resilience (Redmond lies near forested areas east of town) may trigger Class A roofing, ember-resistant vents, and vegetation clearance per state wildfire rules — though these are design recommendations, not hard blocks.
Timeline and fees. Redmond's Building Department reviews ADU applications under a 20-30 day turnaround for standard projects, longer if design revisions are needed. Total permit cost ranges from $3,000 to $8,000: base building permit ($1,200–$2,500, calculated as 0.7%–1.2% of project valuation), plan-review fee ($600–$1,500), utility review ($200–$400), and on-site inspection fees (included in permit). If you use a pre-approved ADU template from the city's website (or from the Washington State Building Code Council's 2023 ADU fast-track sets), expect a 10-day review instead of 20-30 days — a real win if you're on a timeline. Owner-builder status is allowed if the ADU is for your own occupancy (principal residence on the lot); if you're owner-building a detached ADU and renting it, the city may require a licensed contractor or third-party inspection. Filing is online via the Redmond permit portal; you'll upload plans (architectural, electrical, mechanical, plumbing, utilities), utility agreements, and a completed ADU checklist. The city's website (redmond.gov/permits) has a downloadable ADU checklist and a link to the pre-approved plan library.
Three Redmond accessory dwelling unit (adu) scenarios
How Washington State Law (RCW 36.70B.140) Changes Redmond's ADU Rules
In 2023, Washington State passed RCW 36.70B.140 to spur ADU creation across the state by handcuffing local governments. The statute explicitly bans cities from requiring owner-occupancy, from imposing parking requirements on ADUs in urban centers or near transit, from requiring lot splits or lot-size minimums beyond those for the principal dwelling, and from charging ADU-specific permit fees (though standard building permits still apply). Redmond, like all Washington cities, had to rewrite its ADU code (Chapter 21.76 ADR) to comply — and the city did so by simply removing those local restrictions wholesale. The practical result: Redmond now allows one detached ADU and one junior ADU per single-family lot in R-1, R-2, R-3, and R-4 zones, with no owner-occupancy requirement, no lot-split mandate, and (in urban areas) no parking requirement. This is a sea change from Seattle or Bellevue, which still impose some design standards and parking thresholds that are technically compliant with state law but heavier than Redmond's.
The 1,200-square-foot size cap for both detached and junior ADUs is a state floor, not a Redmond ceiling — Redmond does not exceed it locally. The state also preempts design standards: Redmond cannot impose ADU-specific design reviews, architectural compatibility rules, or exterior material requirements that differ from the principal dwelling. However, Redmond can still enforce IRC egress, foundation, and fire-safety codes, and can require site-plan review if setbacks, drainage, or utilities need verification. The upshot is that an ADU permit in Redmond is typically a straight building permit with one plan-review cycle, not a multi-step design + use permit process. If you use a pre-approved template (Washington State or city-curated), you can trigger a 10-day expedited review — a real advantage over cities that require full discretionary design review.
One nuance: state law does NOT prohibit cities from regulating ADUs through zoning overlays (historic districts, flood zones, critical areas) or local health/safety codes. Redmond does have a Historic Landmark District overlay on central Redmond (1900s Craftsman homes); ADUs in that zone must match exterior materials and roof pitch of the principal dwelling (not a preemption violation, since it applies to all residential structures, not just ADUs). Similarly, ADUs in the Sammamish River floodway (east side of town) must meet floodplain elevation and wet-floodproofing per IBC Chapter 3, Appendix G — again, not an ADU-specific rule. These overlays rarely kill ADU projects in Redmond, but they do add 1–2 weeks to plan review and may require engineering (floodplain certification, flood-venting calcs, etc.).
Redmond's Climate, Soil, and Utility Quirks That Affect ADU Costs
Redmond straddles two climate zones: west side (Puget Sound foothills, 4C, 12-inch frost) and east side (volcanic/glacial-till plateau, 5B, 30-inch frost). This matters hugely for foundation cost. A slab-on-grade ADU in west Redmond (say, near Marymoor Park) can use a simple frost-protected shallow foundation (FPSF) — 12 inches of insulation under the slab perimeter or 12 inches of frost protection with perimeter sand — a $1,500 add. The same ADU on the east side (near the Sammamish River, 5B climate, volcanic soil with 30-inch frost) needs 30-inch protection: either a full 30-inch stem wall with footings below frost, or a FPSF with 4 feet of XPS foam around the perimeter — $2,500–$3,500 extra. The city building inspector will ask for a geotechnical report or soils test (≈$400–$800) if the lot has not been permitted before. East-Redmond ADU builders often go with a post-and-pier system to avoid deep frost footings — a reasonable cost trade-off.
Utilities are a wild card. West Redmond (Puget Sound side) has mature municipal water and sewer infrastructure; a typical lot has adequate capacity for an ADU without main-line upgrades. East Redmond (east of 228th Avenue) is more varied: some areas are on municipal sewer + water, others are on individual septic/well systems. If your property is on septic, a new ADU triggers a new perc test (≈$500–$800) and a system expansion review by King County Health — often doable, but if the original septic is marginal, you may need a drainfield expansion or a new tank ($8,000–$15,000). The city will not issue ADU permit until perc results are submitted. Similarly, if on a private well, the ADU is a second dwelling, so the well must be tested for adequate yield (typically ≥5 GPM per dwelling); if the well is low-yield, you'll need a storage tank or a second well (expensive, $3,000–$8,000).
Electrical-service capacity is another pinch-point. Most older Redmond homes (built 1970s–1990s) have 100A service — barely adequate for a principal dwelling, stretched thin with an ADU. The city building inspector will require a service upgrade to 150A or 200A (≈$1,500–$2,500, plus a Puget Sound Energy interconnection fee). If you're on a tight budget, a 100A sub-panel and separate meter (sub-metering) is a cheaper option ($600–$1,200) and makes the ADU's electrical load independent. However, sub-metering adds complexity: the ADU tenant's electrical bill is separate, and you need a sub-meter (≈$250–$400) plus an upgrade to the main panel to accommodate the new circuit (≈$300–$500). Most ADU owners in Redmond do a full 200A service upgrade for long-term flexibility and simplicity.
15670 Redmond Way, Redmond, WA 98052
Phone: (425) 556-2700 | https://www.redmond.gov/permits
Mon-Fri 8:00 AM – 5:00 PM (verify holiday closures on website)
Common questions
Can I rent out my ADU in Redmond, or does Washington law require owner-occupancy?
No owner-occupancy requirement — RCW 36.70B.140 preempts that. You can rent out a detached ADU or junior ADU without living on the property yourself. Redmond allows owner-builder status only if you are the occupant (not absentee-landlord-owner-builder), but the ADU can be rented immediately after final inspection. If you are financing the ADU with a mortgage, confirm with your lender that they accept rental-use ADUs; most banks now do, but some require owner-occupancy as a loan condition.
Do I need separate utility connections for my ADU, or can it share meters with the main house?
Separate metering is required for each utility (water, sewer, electric, gas if applicable). The ADU must have its own water meter, its own sewer connection (or point-of-use treatment if on septic), and its own electric meter or a sub-meter from the main panel. Gas can be on a sub-meter if the ADU shares a gas line with the principal dwelling, but water and sewer must be separately tracked for code compliance and billing. The city will not issue a final utility sign-off without photographic evidence of separate service entrances.
How much does an ADU permit cost in Redmond, and what is included?
Expect $3,000–$8,000 in total permit and review fees: base building permit ($1,200–$2,500, depending on ADU valuation), plan-review fee ($600–$1,500), utility review ($200–$400), and inspection fees (included in permit, typically $800–$1,200 for 5–6 inspections). If you use a pre-approved ADU template, expect a 10-day expedited review with lower plan-review costs (≈$800). Additional costs: electrical service upgrade ($1,500–$2,500 if needed), utility line extensions (if off-grid or septic, $2,000–$15,000), and geotechnical report for hillside or poor-soil sites ($400–$1,200).
What is the timeline for an ADU permit in Redmond — how long from application to final inspection?
Plan review typically takes 20–30 days; expedited (pre-approved templates) is 10 days. Once approved, construction timelines vary (4–6 months for detached, 3–4 months for garage conversion, depending on complexity and weather). Total calendar time from permit application to final inspection and occupancy: 4–6 months for straightforward projects, 6–8 months if utilities require upgrades or site conditions (hillside, poor soil) necessitate engineering review. In winter (November–March), add 2–4 weeks for weather delays and inspector scheduling.
Do I need parking for my ADU in Redmond?
It depends on location. Redmond's code (per RCW 36.70B.140) requires one off-street parking space in suburban R-2, R-3, and R-4 zones but waives it in R-1 zones, urban centers (Town Center, downtown), and within 1/4 mile of light-rail stations or frequent-transit corridors. If parking is required, one 9×18-foot space suffices (tandem or in-driveway acceptable). Check your property's zone and proximity to transit on the city's interactive map (redmond.gov/maps). If required and you cannot fit a space, apply for a parking variance (small fee, usually approved for transit-accessible properties).
Can I build a junior ADU and a detached ADU on the same lot, or is it one-or-the-other?
One or the other, not both. Redmond's code allows one detached ADU OR one junior ADU (interior second unit) per single-family lot, not both simultaneously. However, if your primary dwelling is a duplex or triplex (which is rare in Redmond), you may be able to add an ADU to one unit; confirm with the building department early. Most single-family lot owners choose either a detached ADU (for rental income, separate tenancy) or a junior ADU (cheaper, minimal exterior work, higher resale appeal to future single-family buyers).
What are the setback requirements for a detached ADU in Redmond?
Detached ADUs follow the same setback rules as principal dwellings: R-1 zones typically 15 feet front, 5 feet side, 20 feet rear; R-2/R-3 zones typically 10 feet front, 5 feet side, 20 feet rear; R-4 (multifamily) has tighter setbacks. Junior ADUs (interior second units) require no additional setback beyond the principal dwelling. Measure from the exterior wall of the structure to the property line. If your lot is small or oddly shaped and setbacks conflict, apply for a setback variance (small fee, 4-week review); these are often approved if the ADU still complies with lot-coverage and shadow regulations.
Do I need to hire a licensed contractor, or can I owner-build my ADU in Redmond?
You can owner-build if the ADU is for your own occupancy (principal residence on the lot). Once you place the ADU for rent or occupancy by others, Redmond requires a licensed general contractor for framing, electrical, plumbing, and mechanical trades (per IBC Chapter 34 and state licensing rules). However, the city may assign a construction supervisor requirement (≈$300–$500 fee) and may require third-party framing inspection if the building inspector flags complexity. If you owner-build, you pull the permit, attend all inspections, and sign off as the responsible party.
Are there pre-approved ADU plans I can use to speed up Redmond's permit process?
Yes. Redmond maintains a library of pre-approved ADU plans on its website (redmond.gov/permits > ADU resources), and the Washington State Building Code Council publishes 2023 ADU templates. Using a city-approved plan cuts plan review to 10 days (instead of 20–30) and typically lowers plan-review fees by $200–$400. These templates comply with all setbacks, egress, fire-separation, and utility-separation rules for Redmond's zones. You'll still need to site the plan to your property (foundation design for your soil/frost depth, utility routing, grading). The city's planning staff can pre-screen your site plan against the template (no formal fee) to confirm fit.
What if my ADU doesn't pass inspection or the city finds it non-compliant during construction?
The building inspector will issue a 'correction notice' detailing the violation (e.g., egress window too small, setback encroachment, electrical sub-panel in wrong location). You have 5–10 business days to cure the violation or submit an appeal/variance request. If you cannot physically fix it (e.g., structure encroaches on setback), you may demolish the non-compliant portion and rebuild to code, or request a variance (4-week process, $300–$500 fee, no guarantee of approval if life-safety is at stake). Egress and fire-separation violations usually cannot be waived — they trigger mandatory compliance. Working with the city's ADU coordinator or a contractor experienced in Redmond permits reduces surprise-rejection risk dramatically.