ADU Permits: Rules, Fees, Timelines

Yes — every accessory dwelling unit requires a permit. There are no exemptions. Whether you're building a detached ADU, converting a garage, adding a junior ADU (a small unit within your existing house), or building above a garage, you need a building permit, often combined with a planning permit and utility approvals. This is one of the few project categories where the answer is always the same: you cannot legally build an ADU without a permit.

What changes dramatically by state and city is what your local government will actually allow you to build. California, Oregon, Washington, and Massachusetts have passed aggressive state-level ADU laws that override local zoning, parking requirements, and owner-occupancy rules. Other states leave ADU regulation entirely to local jurisdictions — which means some cities allow them freely and others ban them outright. Before you file anything, you need to know whether your city even permits ADUs. If it does, the state law often makes the process faster and cheaper than it would be otherwise.

The permit process itself is substantial. Expect 6 to 14 weeks from application to approval, full building inspections (foundation, framing, rough trades, final), utility connections or sub-metering, and planning department sign-off. Costs run $3,000 to $15,000 combined — permit fees, plan review, impact fees, and utility connections. Some of this is fixed; much depends on whether you're doing new construction or conversion, and whether your state's ADU law waives parking and owner-occupancy requirements.

The fundamental decision tree is narrow: Does your city allow ADUs? If yes, what type? If you can build it, the permitting path is straightforward — but mistakes in setbacks, utility design, or egress will trigger rejections. This page explains the requirements and walks you through the common hang-ups.

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ADU permit requirements and thresholds

Every ADU — regardless of size, type, or whether it's owner-occupied — requires a building permit. This is mandatory. The permit process typically includes a building permit from the building department, a planning permit or conditional-use permit (if required locally), and utility approvals or sub-meter installation. Some jurisdictions bundle these; others require you to sequence them (planning sign-off first, then building permit, then utility). The critical first step is not the permit application — it's the zoning check. Visit your city's planning department website or call and ask: Are ADUs allowed in my zoning district? If the answer is no, you cannot build one. Period. If the answer is yes, ask the second question: What are the local requirements (size limit, setback, parking, owner-occupancy)? Many cities still have restrictive local rules, even in ADU-friendly states. State law can override local restrictions in several key states. California's ADU laws (Government Code 65852.22 for full ADUs, 65852.26 for junior ADUs, and 65852.2 for multifamily properties) permit ADUs in virtually all residential zones and waive parking requirements in most cases. Oregon HB 2001 (2019) requires cities to allow at least one ADU per lot in residential zones and waives owner-occupancy. Washington HB 1923 (2019) permits up to two ADUs per lot in single-family zones. Massachusetts ADU law (MGL c. 40, sections 3 and 3A) allows owner-occupied ADUs in single-family zones. Colorado, Minnesota, and other states have weaker ADU protections — some local jurisdictions still ban them or require variances. If your state has an ADU law, it typically preempts (overrides) local zoning restrictions, though local setback, parking, or utility requirements may still apply.

Accessory dwelling units come in four main categories, each with slightly different permit implications. Detached new construction is a freestanding structure on the same lot as the primary dwelling. It triggers full building code requirements: foundation (IRC R401–R408), framing, electrical, plumbing, mechanical, and fire-separation distance to property lines (typically 5 or 10 feet, depending on construction type and local code). Setback violations are the #1 rejection reason for detached ADUs — most lots are too small or too narrow to fit a detached unit while meeting side-yard and rear-yard setbacks. You'll need a survey to confirm property lines and a site plan showing the footprint, setbacks, and parking (if required). Garage conversions preserve the foundation but convert an attached or detached garage into living space. This requires egress (typically two means of egress per IRC R310 — a door and a window, or two doors), kitchen and bathroom installation, mechanical and electrical upgrades, and fire-separation from the primary dwelling if attached. Attached garage conversions sometimes trigger fire-wall or fire-rating requirements. You'll need to show that the conversion doesn't eliminate the parking required for the primary dwelling (unless your state law waives this). Junior ADUs (also called accessory dwelling units within the primary dwelling, or ADUs-in-house) are a separate, self-contained unit carved out of the primary house — typically a basement apartment, second-unit upstairs, or converted den with its own kitchen, bathroom, and entry. Junior ADUs usually trigger building code updates to egress, mechanical, and utility separation. They're smaller (CA limits them to 500 square feet) and often cheaper to permit than detached units because they reuse the primary dwelling's foundation and footprint. Above-garage or above-basement ADUs sit on top of existing structures. These require structural analysis (will the existing foundation and structure support the new weight?), full egress and mechanical design, and often a re-inspection of the underlying structure. This category has higher engineering costs but avoids setback issues.

Egress (safe exit routes) is the most common reason ADU permits get held up or rejected. Every bedroom requires two independent means of egress. IRC R310.1 requires at least one egress window (or door to grade). The second is typically the primary entry door. Egress windows must have a sill height of 44 inches or less, a clear opening of at least 5.7 square feet, and be reachable without moving furniture or navigating obstructions. Basement and ground-floor rooms often fail because the egress window is too small, positioned too high, or blocked by bars or landscaping. Show egress clearly on your floor plan: dimension the window, label it "egress window," and mark its distance from the property line. Do not assume the bedroom door alone counts as two means of egress; it doesn't. Utility connections or sub-metering is mandatory and often triggers rejections because homeowners don't plan for it. New detached ADUs require separate water, sewer, and electrical service — or sub-meters (separate meters fed from the primary dwelling's service) if your utility company permits it. Sub-metering is cheaper and faster than running separate utility lines but requires coordination with your water and electric providers. Some jurisdictions mandate separate utilities; others allow sub-metering. Ask your local water and electric utilities what they require before you file; include their written approval (or sub-metering plan) with your permit application. Garage conversions sometimes reuse the primary dwelling's utilities if the conversion is small and the utility company approves; most detached ADUs cannot. Setbacks and lot coverage are strict. Detached ADUs must meet side-yard (typically 5 feet), rear-yard (typically 10–20 feet), and setback-from-front-lot-line (typically 25 feet) requirements. Some ADU-friendly states (like California under certain conditions) reduce these for ADUs, but local setback ordinances still apply. Many residential lots are too small or shaped awkwardly to fit a detached ADU. Measure your lot, know the required setbacks from your zoning ordinance, and calculate whether a detached ADU fits. Use a site plan or aerial photo to visualize this — don't guess. If a detached ADU won't fit, pivot to a garage conversion or junior ADU. Fire sprinklers are triggered by total square footage on the lot, not just the ADU. If the primary dwelling plus the ADU exceeds 5,000 square feet, IRC R313 typically requires sprinklers (or local code may require them at a lower threshold). Some jurisdictions waive this for small ADUs or if the primary dwelling already has sprinklers. Check your local code; if sprinklers are triggered, budget $1,500–$3,000 for design and installation.

Foundation and construction-type requirements depend on whether the ADU is detached or attached, and whether you're in a wildfire or seismic zone. Detached ADUs must be fully engineered: foundation design must account for the frost depth (which varies by region — 48 inches in Wisconsin, 36 inches in many parts of California), soil conditions, and local seismic or wind-load requirements. A structural engineer will charge $800–$2,000 for the foundation design. Attached units (garage conversions, above-garage) must show proof that the existing structure can support the new weight and use; this often requires a structural review of the existing foundation. Wildfire and seismic zones add requirements. In wildfire zones (parts of California, Oregon, Washington, Colorado), exterior walls must use fire-resistant materials, metal roofing or Class A shingles, and ember-resistant venting (IRC R327). In seismic zones (California, Oregon, Washington, parts of Colorado), the structure must comply with seismic design standards; detached ADUs on soft soil may require additional bracing or foundation work. These are not optional — if you're in a high-risk zone, the local building department will require them, and skipping them will trigger a rejection.

Owner-occupancy requirements vary by state. California, Oregon, and Washington have largely waived owner-occupancy rules (you can build a fully detached ADU and rent it out from day one without living on the property). Massachusetts requires the owner to occupy either the primary dwelling or the ADU. Many states leave owner-occupancy to local choice; some jurisdictions still require the owner of the primary dwelling to live on the lot. Ask your local planning department: Is owner-occupancy required? If yes, will you need to certify it, and for how long (1 year, 5 years, permanently)? Some jurisdictions require a legal agreement or covenant running with the land. Rent control and deed restrictions are separate from permits but often come up during planning review. A few cities (Los Angeles, San Francisco, Oakland, Berkeley) have rent-control rules for ADUs. Others require you to keep the ADU affordable for a set period (often 15–55 years) or impose deed restrictions limiting who can occupy it. These are planning-level rules, not building-permit rules, but they'll affect your decision to build. Ask the planning department: Are there any restrictions on renting out the ADU, or requirements to keep it affordable?

How ADU permits and laws vary by state

California has the most aggressive ADU law in the nation. Government Code 65852.22 (full ADUs), 65852.26 (junior ADUs), and 65852.2 (ADUs in multifamily zones) preempt local zoning, height, setback, and parking rules in most cases. You can build a detached ADU as-of-right (no conditional-use permit required) on any single-family lot, waiving parking and reducing setback requirements. Junior ADUs are capped at 500 square feet or 25% of the primary dwelling, whichever is smaller. Plan review is subject to a 60-day shot clock (per AB 671 and AB 881), meaning the city must approve or reject within 60 days or the permit is deemed approved. Pre-approved ADU plans (available through the state) fast-track review to 20 days. Owner-occupancy is not required. Impact fees are typically capped or waived. Cost: $2,000–$8,000 for permit, plan review, and utility connections; engineering $1,000–$3,000. Timeline: 6–10 weeks if you use pre-approved plans; 10–14 weeks for custom designs. Oregon HB 2001 (2019) requires all cities to allow at least one ADU per lot in single-family zones. The law preempts parking requirements and owner-occupancy rules. Detached and attached ADUs are permitted as-of-right; local setbacks and design standards still apply, but cities cannot ban ADUs or impose unreasonable restrictions. However, cities can still impose lot-size minimums (typically 5,000–7,500 square feet), so many suburban and rural lots in Oregon still cannot accommodate detached ADUs. Junior ADUs are permitted in single-family zones with minimal restrictions. Cost: $2,500–$10,000 (Oregon cities vary widely); timeline: 8–12 weeks. Washington HB 1923 (2019) allows up to two ADUs per single-family lot, with relaxed parking and setback rules. Detached ADUs up to 1,200 square feet are permitted; conversion of existing structures (garages, sheds) are fast-tracked. Owner-occupancy is not required. However, local design review and utility capacity review still apply, and some jurisdictions have raised permit fees to offset ADU growth. Cost: $3,000–$12,000; timeline: 8–14 weeks. Massachusetts allows owner-occupied ADUs in single-family zones (MGL c. 40, sections 3 and 3A) without a variance, but the owner must occupy one of the units. This effectively prohibits investor ADUs unless the structure is rented as a whole. Local building departments still review setbacks, parking, and utilities. Cost: $1,500–$8,000 (varies by municipality); timeline: 8–12 weeks. Colorado HB 19-1174 permits ADUs in single-family zones but gives cities local control over parking, owner-occupancy, and size limits. Some cities (Boulder, Denver, Fort Collins) welcome ADUs; others still restrict them. Always confirm with your city planning department. Cost: $2,000–$10,000; timeline: 8–16 weeks. Minnesota, New Hampshire, Connecticut, and other states have weak or no statewide ADU laws. Regulation is purely local — some cities allow ADUs easily; others ban them or require variances. There is no shot clock; plan review can take 12–20 weeks. Cost: $2,500–$15,000 (higher in expensive markets); timeline: 10–20 weeks. Texas, Florida, and other Southern states have minimal ADU protection. ADUs are treated like secondary dwelling units or guest houses and are often restricted to owner-occupancy only or prohibited entirely in single-family zones. Check your city first; many won't allow them. Cost: $2,000–$10,000 if permitted; timeline: 10–16 weeks.

Common scenarios

Detached new ADU on a standard suburban lot (California example)

You own a 7,000-square-foot lot in Sacramento with a 1950s single-family home. You want to build a 700-square-foot detached ADU in the backyard. Under California's ADU law, you don't need a conditional-use permit or variance. You file a building permit with a floor plan, site plan (showing the footprint, setbacks, and parking), structural foundation design (engineer-stamped), electrical and plumbing plans, and utility sub-metering plan. You contact Sacramento Municipal Utility District and confirm sub-metering is allowed. You pay $1,200 for the permit, $800 for plan review, $150 for utility connections, and $1,500 for the structural engineer. Timeline: 8–10 weeks. The building department issues the permit and schedules foundation, framing, rough-trades, and final inspections over the next 4–6 months as you build.

Garage conversion to ADU (mixed state example)

You have a detached 600-square-foot garage in Oregon. You want to convert it to an ADU. Oregon HB 2001 permits conversion of existing structures as-of-right in single-family zones. You don't need a parking variance (because HB 2001 waives parking). You file a building permit with conversion plans, showing: egress windows in all bedrooms (sill height 44 inches or less, clear opening at least 5.7 square feet), plumbing layout for a new bathroom and kitchen, electrical service upgrade, roof/wall condition assessment, and utility connection or sub-metering. Your city may require architectural review (if the conversion is visible from the street). You pay $1,500 for the permit, $600 for plan review, and $200 for a re-roof inspection (if needed). Timeline: 6–8 weeks. Build phase: 8–12 weeks, including framing, MEP rough-in, drywall, and inspections.

Junior ADU carved from primary dwelling (California example)

You have a 2,500-square-foot house in San Jose with a basement that's currently unfinished. You want to partition off 400 square feet as a junior ADU with its own entry, bathroom, and kitchenette. California limits junior ADUs to 500 square feet or 25% of the primary dwelling (whichever is smaller), so 400 square feet is permitted. You file a building permit with floor plans showing the new unit, egress windows (two per bedroom per IRC R310), separate mechanical/electrical/plumbing serving the new unit, and the layout of the primary dwelling to confirm the primary unit still has its own kitchen and living space. No parking is required. You pay $800 for the permit, $400 for plan review, and $1,200 for MEP design and permit fees. Timeline: 6–8 weeks. Build phase: 6–10 weeks.

Detached ADU on a small lot (setback violation)

You own a 4,500-square-foot lot in a single-family zone that requires 10-foot side yards and 20-foot rear yards. You want to build a detached 600-square-foot ADU. The lot is only 40 feet wide (meaning 10 feet on each side is 20 feet total) and 110 feet deep. A 600-square-foot ADU at roughly 25 feet × 24 feet won't fit: it violates the rear-yard setback by at least 5 feet. You file a permit anyway, and the building department rejects it: 'Proposed structure does not meet minimum rear-yard setback of 20 feet.' You have two options: apply for a variance (expensive, time-consuming, and often denied) or pivot to a garage conversion or junior ADU that doesn't require new footprint or setback compliance.

Detached ADU in a city that bans them

You live in Minneapolis and own a single-family lot. You want to build a detached ADU. Minneapolis has no local ADU ordinance, and Minnesota has weak state-level ADU protection. You call the city's planning department and ask: 'Can I build an ADU?' The answer is no — the city's zoning ordinance permits only one dwelling unit per single-family lot. You can apply for a variance, but variances require proving that the property has unique hardship, which is difficult. Your only option is to wait for the city to change its zoning (which may happen in the next few years) or choose a different project.

Above-garage ADU with structural concerns

You have a 1970s single-car garage (16 feet × 20 feet, with a 4-inch concrete slab and no reinforcement) and want to build a 500-square-foot ADU on top. A structural engineer evaluates the garage and finds the slab is undersized and the foundation is not designed to support a second story. The engineer estimates $8,000–$12,000 in foundation work (removing the slab, pouring a new reinforced slab, adding footings and a grade beam). You decide to proceed. You file a building permit with the engineer's report and revised foundation design. The building department approves, conditioned on a foundation inspection before framing. Timeline: 8–12 weeks for permit, 16–20 weeks for construction (foundation work is substantial). Cost: $12,000 foundation, $2,000 permit, $2,000 plan review, $8,000 MEP design.

Documents you'll need and who can pull the permit

Document	What it is	Where to get it
Site plan or survey	A drawing showing property lines, the footprint of the primary dwelling, the proposed ADU, setbacks from property lines, parking spaces (if required), and any easements or encroachments. For detached ADUs, this is mandatory to prove setback compliance. For conversions, it confirms the location of the work.	A surveyor (cost $400–$800 for a simple site plan, $1,200–$2,500 for a full survey) or an architect/designer (included in design package, cost $1,500–$5,000 for full ADU design). If you already have a survey on file from a prior transaction, provide it.
Floor plans and elevations	Architectural drawings showing the layout of the ADU (all rooms, dimensions, door/window locations), ceiling heights, and exterior elevations. Plans must show egress windows and doors clearly labeled, kitchen and bathroom fixtures, mechanical/electrical panel locations, and any structural changes (for conversions).	An architect or designer. For pre-approved ADU plans (available in California), you can purchase plans for $300–$1,500 and submit them as-is with minimal local customization.
Electrical plans	A diagram showing the service panel (main or sub-panel), circuits, outlet locations, light fixtures, and any hard-wired appliances. The plan must show separate service or sub-metering if required.	An electrician or electrical designer (cost $300–$800). An architect's plan package usually includes a simplified electrical layout; your electrician will provide the detailed plan for permit.
Plumbing plans	A diagram showing the kitchen, bathroom(s), water supply lines, drain/waste/vent (DWV) lines, and how the unit connects to water and sewer (separate utility or sub-meter). Must show the size and location of the water meter and sewer connection.	A plumber or plumbing designer (cost $400–$1,000). Some architects include a basic plumbing layout in the design package.
Mechanical/HVAC plans	A diagram showing heating/cooling distribution, ventilation (especially bathroom exhaust and kitchen hood venting to exterior), and any ductwork or mechanical units. For detached ADUs, you often need a separate HVAC unit.	An HVAC designer or contractor (cost $400–$1,000, or included in design package). Some jurisdictions allow simplified mechanical plans for small ADUs.
Foundation design (for detached ADUs)	An engineer-stamped drawing showing footing depth, size, reinforcement, and frost-depth compliance. Must account for local soil conditions, seismic/wind loads, and frost depth. Required for all detached new construction.	A structural engineer (cost $800–$2,500). Provide soil-boring data if the engineer requests it (cost $500–$1,500 for boring and testing).
Utility connection approval or sub-metering plan	Written confirmation from your water and electric utilities that they will allow sub-metering or separate service. If utilities refuse sub-metering, you must run separate lines (cost $2,000–$5,000). Include this approval with your permit application.	Contact your local water and electric utilities directly. Ask: 'Can I sub-meter an ADU?' or 'What is required for separate electrical service?' Get written confirmation (email is fine) and attach it to your permit application.
Egress window details (if bedrooms)	Detailed drawings showing the size, sill height, and clearance of any bedroom egress windows. IRC R310.1 requires a sill height of 44 inches or less and a clear opening of at least 5.7 square feet (often a 30-inch × 36-inch window). Show obstruction-free space around the window.	Your architect or designer includes this in the floor plan. Confirm with the window manufacturer that the window meets IRC R310.1 before ordering.
Fire-rated wall or separation details (for attached conversions)	If converting an attached garage, the city may require a fire-rated wall between the garage and the ADU (or between the ADU and the primary dwelling). Show the wall construction, insulation, fire-rating, and how penetrations (ducts, pipes) are sealed.	Your architect or structural engineer. The detail is standard (often 1-hour fire-rated wall per IRC R302) and costs nothing extra to include on the plans.
Pre-approved ADU plan (if available)	In California, HCD (Department of Housing and Community Development) publishes free and low-cost pre-approved ADU plans that local agencies must review and approve within 20 days. Plans are complete, code-compliant, and fast-track the process significantly.	California HCD website (hcd.ca.gov) — free. Or purchase from private vendors (e.g., Blokable, ADU-It) for $300–$1,500. Other states do not have pre-approved plans (yet).

Who can pull: In most states, homeowners can pull their own permits and be the applicant. However, the responsible party for construction and design submittals is often required to be a licensed architect, engineer, or contractor. Check your local code: some jurisdictions require a licensed professional to stamp and sign off on structural, electrical, plumbing, and MEP plans. In owner-builder-friendly states (California, Oregon, Washington), homeowners can be the contractor, but plans must still be signed by a licensed professional (engineer or architect). If you plan to hire a contractor, the contractor's name will be on the permit as the responsible party for construction, but the permit applicant can still be you (the owner). Avoid confusion: contact your building department and ask 'Can a homeowner be the applicant and the contractor, or do I need to hire a licensed contractor?' Answers vary by jurisdiction.

Common ADU permit rejections and fixes

Proposed structure violates required setback (detached ADU too close to property line or rear yard).
Measure your lot and calculate available space. If a detached ADU won't fit, pivot to a garage conversion, junior ADU, or above-garage unit that doesn't require new footprint. If you still want detached, apply for a variance (expensive, time-consuming). Confirm setback requirements with your zoning ordinance before designing.
Insufficient egress windows (bedroom without proper egress window, or sill height too high, or opening too small).
IRC R310.1 requires a sill height of 44 inches or less and a clear opening of at least 5.7 square feet. Install a standard 30-inch × 36-inch window or larger. Do not rely on doors alone — every bedroom needs a window. Show the window clearly on the floor plan with dimensions and sill height marked.
Utility connections or sub-metering not approved or shown on plans.
Contact your water and electric utilities BEFORE filing the permit. Get written confirmation that sub-metering is allowed (or that separate service is required and feasible). Include this approval with your permit application. Show the meter location and connection on the plumbing and electrical plans.
Owner-occupancy requirement not waived or certified (in states that require it).
If your state or city requires owner-occupancy, ask the planning department: Is this required? If yes, for how long? Some states (CA, OR, WA) have waived this; others (MA, some local jurisdictions) still require it. If required, you may need to sign an affidavit that you will occupy one of the units, or record a covenant on the property.
Parking requirement not satisfied (often applies to conversions if the conversion eliminates parking for the primary dwelling).
Most ADU-friendly states (CA, OR, WA) waive parking for ADUs. If your jurisdiction still requires it, show parking spaces on the site plan: one space per bedroom (minimum). If you can't fit parking, apply for a parking variance or check whether your state law waives it.
Fire sprinklers triggered by combined square footage on lot but not shown on plans.
Add up primary dwelling + ADU square footage. If it exceeds your local threshold (often 5,000 sq ft per IRC R313), sprinklers are required. Check your local code. If triggered, hire a fire-protection engineer to design the system (cost $1,500–$3,000) and add to your permit. Some jurisdictions waive sprinklers for small ADUs or if the primary dwelling already has them.
Existing garage conversion: structure not capable of supporting ADU use (foundation inadequate, structural framing undersized).
Have a structural engineer evaluate the existing building (cost $500–$1,200). If the structure is inadequate, the engineer will specify reinforcement or foundation work. Budget $5,000–$15,000 for structural upgrades. Submit the engineer's report and revised plans with your permit application.
No survey or site plan showing property lines and setbacks (for detached ADUs).
Hire a surveyor or have an architect draw a site plan showing property lines, existing dwelling, proposed ADU footprint, setback dimensions, and easements (cost $400–$800). This is mandatory for detached units and strongly recommended for conversions.
Architectural or design details missing (window schedules, door schedules, room dimensions, ceiling heights).
Complete the floor plan and elevations with all dimensions, window/door tags and schedules, finished floor levels, and exterior materials. Building departments won't process incomplete plans. Hire an architect or designer if you're not confident in drafting.
Separate utility connections or sub-metering shown but utility company has not approved the method.
Call or email your water and electric utilities and ask: 'What is your requirement for sub-metering an ADU?' or 'Can I install a separate meter?' Get written approval before filing the permit. Include the utility's approval letter with the application.

ADU permit fees and overall costs

ADU costs are split into three categories: permit and plan-review fees (charged by the building department), impact and connection fees (charged by the city or utilities), and design and engineering (hired by you). Permit fees alone typically run $1,200–$3,500, but when combined with impact fees, utility connections, and design, total permitting costs are $3,000–$15,000. The wide range reflects differences in state law (California is much cheaper due to fee caps and shot-clock rules), city size (larger cities charge more), and project scope (a simple garage conversion is cheaper than detached new construction).

Permit fees are often based on project valuation. Most jurisdictions charge 1.5–2% of estimated construction cost as the permit fee. If your ADU costs $150,000 to build, permit fees might be $2,250–$3,000. However, many ADU-friendly states cap fees. California caps permit fees at $750–$2,000 depending on structure type. Washington and Oregon have similar caps. Cities without ADU-specific fee caps charge higher fees to offset the work.

Impact fees (also called development fees, system development charges, or connectivity fees) are separate from permit fees. Cities charge these to offset infrastructure costs (water, sewer, traffic, parks). Impact fees can be $2,000–$8,000 depending on the city. Many ADU-friendly states partially or fully waive impact fees for ADUs under certain conditions. For example, California waives impact fees for ADUs if the ADU is affordable or if the primary dwelling is within a disadvantaged community. Oregon waives most impact fees for ADUs in single-family zones. Ask the city planning department: 'Are impact fees required for my ADU? Are there any waivers?'

Utility connections (water, sewer, electric) cost $1,500–$5,000. This depends on whether you're sub-metering (cheaper) or running separate lines (more expensive). Sub-metering requires coordination with utilities but typically costs $200–$1,000. Separate service (water, sewer, gas, electric all new) can cost $2,000–$8,000 if the ADU is far from the primary dwelling or if the utility company charges connection fees. Get quotes from your utilities before finalizing your budget.

Line item	Amount	Notes
Building permit (base)	$1,200–$3,500	1.5–2% of project valuation, capped in CA, OR, WA. Higher in cities without ADU-specific fee caps.
Plan review	$500–$1,500	May be bundled into permit fee. Separate in some jurisdictions. Faster (20–40 days) in CA due to shot clock.
Impact and development fees	$0–$8,000	Waived or reduced in CA, OR, WA for ADUs. Full impact fees in other states (add $2,000–$8,000).
Utility connections (water, sewer, electric)	$200–$5,000	Sub-metering ($200–$1,000 cheaper) vs. separate service ($2,000–$5,000). Depends on utility distance and utility approval.
Architectural/design plans	$1,500–$5,000	Architect or designer for floor plans, MEP drawings, elevations. Cheaper ($500–$1,500) if using pre-approved ADU plans (CA only).
Structural engineering (detached ADU or foundation upgrade)	$800–$2,500	Required for detached new construction. Add $500–$1,500 for soil boring/analysis if needed.
Building inspections (included in permit)	$0	Foundation, framing, rough trades, final inspections are included in permit fee. Re-inspections after rejection cost $100–$300 each.
Variance or conditional-use permit (if needed)	$800–$3,000	If setback or design variance required. Application, hearing, legal notices. Only if local code doesn't allow as-of-right.
TOTAL permitting cost (typical range)	$3,000–$15,000	Low end: CA garage conversion with pre-approved plans. High end: detached ADU in non-ADU-friendly state with variances and full utility work.

Common questions

Can I build an ADU without a permit?

No. Every ADU requires a building permit. There are no exemptions. Building without a permit is illegal and will result in a stop-work order, fines ($1,000–$5,000+), and an expensive forced demolition or legalization process. If an inspector discovers unpermitted work, you'll face back-taxes, unpermitted-work penalties, and difficulty selling or insuring the property. Permit first, always.

Does my city allow ADUs?

You have to ask. Call your planning department or check the city's zoning ordinance online. Ask: 'Are accessory dwelling units allowed in my zoning district?' Many cities still prohibit them in single-family zones. If your state has an ADU law (CA, OR, WA, MA, CO), it may override the local ban, but you still need to confirm. If ADUs are not allowed and no state law covers you, you cannot build one legally — period.

What's the fastest way to permit an ADU?

In California, use a pre-approved ADU plan (free from HCD or $300–$1,500 from vendors). Pre-approved plans must be approved within 20 days. In Oregon and Washington, garage conversions and above-existing-structure ADUs are faster than detached new construction (which requires foundation design). Across all states, simple projects (conversions, junior ADUs) are faster than detached new construction (which requires full structural design and engineering). Timeline: detached new 10–14 weeks, conversion or above-garage 6–10 weeks.

Can I live in the ADU while I'm building it?

No. The permit is issued for new construction, not occupancy. You cannot legally occupy the unit until the final inspection is passed and the building department issues a certificate of occupancy. Occupying before final sign-off is a code violation and subjects you to fines and a stop-work order. Wait for final inspection and occupancy approval.

Do I need a contractor or can I do the work myself?

It depends on your state and whether you're classified as an owner-builder. California, Oregon, Washington, and most states allow homeowners to do their own work and pull permits as owner-builders. However, you must still hire licensed professionals for certain trades (electrical, plumbing, HVAC, gas in some states). Some jurisdictions prohibit owner-builders entirely or limit them to single-family residences (which would exclude ADUs if the ADU is considered a separate unit). Check your city's owner-builder policy. Regardless, you need licensed professionals to design and stamp plans (architect or engineer for structural, engineer for MEP in many jurisdictions).

What is a shot clock and why does it matter?

A shot clock is a legal deadline within which a city must approve or deny a permit application. California's ADU law (AB 671 and AB 881) imposes a 60-day shot clock for ADU applications. If the city doesn't approve or deny within 60 days, the permit is automatically deemed approved. This speeds up the process and prevents indefinite delays. Oregon and Washington have similar timelines (around 90 days for most land-use decisions). States without shot-clock rules can take 12–20 weeks to approve or deny. If you file in California and the 60-day deadline is approaching, the city may approve your permit to meet the deadline even if there are minor details pending.

How much does an ADU cost to build (not including permit)?

Construction costs vary widely by region, labor availability, and design. A modest 500–700-square-foot detached ADU typically costs $150,000–$350,000 to build (materials + labor). Garage conversions are cheaper: $80,000–$200,000 depending on the extent of work. Junior ADUs: $50,000–$150,000. A-grade finishes and expensive regions (SF Bay Area, Seattle, LA) push costs higher ($300,000–$500,000 for a basic detached ADU). Permits and site prep add 5–15% on top. Get quotes from local contractors for a real estimate.

Can I rent out my ADU immediately after getting a permit?

No. You must wait for the final inspection and certificate of occupancy. Once you have occupancy approval, you can rent it out immediately in most states. However, some jurisdictions have rent-control or affordable-housing requirements that restrict who you can rent to or how much you can charge. Ask your planning department: 'Are there any restrictions on renting the ADU, or requirements to keep it affordable?' In some cities (LA, SF, Oakland, Berkeley, etc.), you may be required to keep the ADU affordable for 15–55 years or accept restricted rent increases.

What happens if I don't get a permit?

Building without a permit is a code violation. Consequences include: stop-work order, fines ($1,000–$10,000+ depending on jurisdiction), forced demolition, back property taxes, unpermitted-work penalties, difficulty selling or insuring the property, and potential legal liability if someone is injured. When you sell, a home inspector will discover unpermitted work, and the buyer's lender will require permits and inspections before funding. The cost to legalize unpermitted work retroactively is often higher than the cost of permitting before you build. Don't skip the permit.

Do I need a separate utility meter for an ADU?

In most cases, yes — either a separate meter or a sub-meter. Local utilities and building codes generally require it for billing and code-compliance reasons. Sub-metering (a meter on the ADU fed from the primary dwelling's main service) is cheaper and often allowed if the utility company approves. Separate service (new utility lines to the ADU) costs more but is sometimes required if the primary dwelling can't support the added load. Before designing, contact your water and electric utilities and ask: 'What is your requirement for metering an ADU?' Get written approval and include it with your permit application.

How long do inspections take?

Each inspection typically takes 1–4 hours (depending on complexity) and the inspector schedules you within 2–5 business days of your request. A typical detached ADU requires 4–6 inspections: foundation, framing, rough trades (electrical/plumbing/mechanical), insulation/drywall, final, and often a planning/fire-marshal sign-off. If an inspection fails (code violation found), you fix the issue and request a re-inspection, adding 1–2 weeks. The total inspection period spans the construction phase (2–6 months depending on scope). You schedule each inspection by calling the building department or using an online portal (if available).

Cities we cover for accessory dwelling units (adu) permits

City-specific accessory dwelling units (adu) permit guides with local fees, code editions, and building department contact info. Click your city for the local rules.

California

Oregon

Ready to move forward with your ADU?

Start with your city's planning department. Call or email and ask: (1) Are ADUs allowed in my zoning district? (2) What are the local requirements (size limit, setback, parking, owner-occupancy)? (3) Does your state have an ADU law that overrides local rules? Get those three answers before you hire an architect or engineer. Then check with your water and electric utilities: what do they require for metering? Once you have those baseline answers, you'll know if your project is feasible and what it will cost. Next step: hire an architect or designer to create the plans. If you're in California, Oregon, or Washington, explore whether your state's pre-approved ADU plans or fast-track process apply to your project — you could save weeks and thousands of dollars. Finally, gather your site plan, utility approval, and design drawings, and file your permit application. Use the scenarios and checklist on this page to make sure you're not missing anything. Most rejections happen because setbacks are wrong, egress is missing, or utility approval is absent — all avoidable with a careful review before submission.

Related permit guides

Other guides in the Additions & conversions category:

Do I need a permit for an accessory dwelling unit (ADU)?