What happens if you skip the permit (and you needed one)
- Stop-work orders and fines: $100–$500 per day in Monterey; unpermitted structures discovered at sale or refinance trigger back-permit fees (often double the original permit cost, $8,000–$16,000) plus lien attachment.
- Insurance claim denial: Your homeowner's policy will deny claims on an unpermitted ADU; lender-mandated homeowners insurance becomes invalid, putting your mortgage at risk of acceleration.
- Title and resale catastrophe: California requires disclosure of unpermitted work via Transfer Disclosure Statement (TDS); buyers will demand removal or massive price reduction ($30,000–$100,000+); some title companies will not insure unpermitted units.
- Neighbor complaints trigger city enforcement: Monterey code enforcement will investigate unpermitted dwelling units reported by neighbors; removal or legalization costs $15,000–$50,000 if structure must be torn down.
Monterey ADU permits — the key details
California Government Code 65852.2, as amended by AB 671 (2021) and AB 881 (2022), mandates that Monterey must approve detached ADUs, garage conversions, and junior ADUs without traditional local discretion. Monterey's 2020 ADU ordinance was written before these state laws took full effect, but the state law now supersedes any conflicting local rule. The city cannot require owner occupancy of the primary dwelling, on-site parking, lot-size minima, setback waivers, architectural review that delays approval, or a conditional-use permit. Your ADU can be up to 1,200 sq ft (or 50% of the primary dwelling's size, whichever is smaller) on any residential lot zoned for single-family or multifamily housing. Detached ADUs must comply with standard setback rules (typically 5 feet side, 10-15 feet rear in Monterey's R-1 zone), but the city cannot impose extra setbacks specifically for ADUs. Garage conversions are allowed even if they reduce parking below the primary unit's requirement.
Plan review in Monterey is capped at 60 days for a 'complete application' per AB 671; most detached ADUs and garage conversions can be reviewed over-the-counter (no architectural review committee) if plans meet code. You'll need a set of stamped plans showing: site plan with property lines and setbacks, floor plan with room dimensions and egress (IRC R310 requires two means of egress or a single egress with a smoke alarm and sprinkler system in bedroom), electrical one-line diagram, plumbing layout, foundation/slab detail, and utility connections (separate water/sewer meters or sub-metering). Monterey's building department uses an online portal (managed through the city's official website); you can upload plans and track status online. The city will issue a 'determination' letter within 15 days acknowledging receipt; if your application is incomplete, the clock stops until you resubmit. Once deemed complete, you have 60 days to permit issuance or a written denial with specific code citations.
Utility connections are a common sticking point. Monterey requires separate water and sewer meters for detached ADUs (not for junior ADUs or garage conversions, which can share the primary dwelling's utilities). Your water provider (California American Water or Monterey Peninsula Water Management District, depending on your location) must confirm availability and agree to a second meter; some areas have water-shortage restrictions, but Monterey does not currently deny ADU meters based on water supply. Electrical can be sub-metered or run as a separate service; plumbing must comply with the 2022 California Plumbing Code. If your ADU has a kitchen (sink, stove, refrigerator), it counts as a 'dwelling unit' and triggers full utility separation and dwelling-unit permits. If it has only a sink and refrigerator (no stove/cooktop), some jurisdictions treat it as a 'junior ADU,' which allows utility sharing — but Monterey's current interpretation requires separate meters even for junior ADUs, so verify with the building department.
Egress and firefighting requirements often trigger plan-review corrections. IRC R310.1 requires at least two means of egress (hallway to main exit + bedroom window) from every bedroom; if you have only one bedroom or a small lot that won't accommodate two egress points, you can use a single egress with an automatic sprinkler system (NFPA 13R or 13) in the ADU. Monterey does not require sprinklers in detached ADUs under 800 sq ft with two means of egress, but many older lots (especially in Pacific Grove or New Monterey) have tight setbacks that force single-egress designs — this triggers sprinkler costs ($3,000–$6,000). Detached ADUs also need a firewall or fire-rated wall separating them from the primary dwelling (1-hour rated per IBC 706); garage conversions require a firewall from the garage (typically 1.5 hours). These details must be shown in construction documents, or plan review will be denied.
Parking is no longer a barrier in Monterey, but you should document the existing situation. AB 671 prohibits Monterey from requiring off-street parking for ADUs in single-family zones; you do not need to provide a new parking space. However, if your property already has designated parking, do not reduce it — the city will flag plans that show removal of primary-unit parking. Detached ADUs built in side or rear yards can be accessed via easement or driveway; the city will want to see a clear access route to the unit. Setbacks must comply with the base zone (5 feet side, 10-15 feet rear for R-1 detached structures), but you cannot be required to request a variance or conditional use permit for setback relief on an ADU — if your lot cannot accommodate the detached ADU with standard setbacks, you must be allowed to build a garage conversion or junior ADU instead (or Monterey must deny for lack of feasible alternative, and you can appeal to the state).
Three Monterey accessory dwelling unit (adu) scenarios
California's ADU state-law preemption: why Monterey cannot say no
In 2016, California passed AB 2299, allowing 'accessory dwelling units' in single-family zones, but it was optional for cities (most said no). In 2020, Governor Newsom signed AB 68, tightening the rules further. But the hammer came in 2021: AB 671 made ADUs 'ministerial' — meaning the city cannot use discretion, architectural review, or conditional-use permits to slow them down. Any ADU that meets the size and code requirements (up to 1,200 sq ft detached, or 50% of primary dwelling size, whichever is less) must be approved within 60 days for detached; 30 days for junior ADUs. Monterey's 2020 ADU ordinance predates AB 671 and contains some local rules (parking, owner-occupancy language) that are now superseded by state law. If you submit an ADU permit application that meets AB 671's criteria, the city cannot deny it based on Monterey's local ordinance provisions that conflict with state law. The city must cross-check your application against California Government Code 65852.2(c) and issue a permit or send a written denial citing only code sections that are not preempted. This is why many Monterey applicants succeed in appeals: the city staff sometimes default to old local rules, but the state law is clear. Owner occupancy is no longer required (as of AB 671); parking is no longer required (AB 671); lot-size minimums do not apply to ADUs (state law). Monterey can still enforce setbacks, fire code, IRC egress, and utility standards, but it cannot create new gates to approval.
The 60-day clock for detached ADUs is a major shift. If Monterey deems your application complete on day 1, the permit must be issued or a detailed denial provided by day 60 (or the application is approved by default). This timeline is enforced by the state Attorney General; Monterey Building Department staff are trained on this, but mistakes happen — if you hit day 60 with no response, you can send a notice of non-response and escalate to the city. In practice, Monterey's competent staff issue most detached ADU permits within 40 days if plans are tight; garage conversions and junior ADUs, which are simpler, often get approved in 20-25 days. The key is submitting complete plans the first time. Incomplete submissions (e.g., no utility connection letter, no egress detail, no firewall specification) restart the clock. Monterey's building department publishes a 'Residential ADU Project Checklist' on its website; use it to avoid resubmittals. Common missing items: proof of utility availability (call your water provider and get a letter), structural calculations if the lot is tight or hillside-sloped, and clarification of whether you have a second means of egress or need a sprinkler system.
State law also limits Monterey's ability to impose impact fees and tax on ADUs. The city cannot charge disproportionate sewer or water connection fees; it can charge normal 'buy-in' fees (roughly $500–$1,200 per new meter in Monterey's jurisdiction). Some older Monterey local ordinance language suggested a 'second dwelling unit fee' or 'ADU registration fee'; these are now unenforceable under state law. However, Monterey may still charge standard building permit and plan-review fees (typically 1.5-2% of valuation), impact fees if they are equally applied to new dwellings, and utility connection fees. The total permit cost is capped by what the city would charge for a new single-family home of equivalent size — so a 1,000 sq ft ADU should not cost more in permits than a 1,000 sq ft new house would. In Monterey, this typically means $6,000–$10,000 in permit/review fees for a detached ADU, plus utility connection costs.
Monterey's coastal climate and hillside constraints: how geography affects your ADU design
Monterey County spans two climate zones: coastal 3B-3C (temperate, maritime, minimal frost) and mountains/inland 5B-6B (cool to cold, 12-30 inches frost depth). If your property is in the City of Monterey proper (Pacific Grove, New Monterey, Del Monte Forest, Seaside portions), you're almost certainly in zone 3B-3C — no frost depth concern, no deep footings required. But if you're in the foothills (Big Sur, unincorporated Carmel Valley, higher elevations), frost depth rises to 12-30 inches, triggering deeper foundation requirements per IRC R403.1.8. Concrete slabs must be thickened at perimeter in frost zones; detached ADU foundations must extend below frost depth or use frost-protected shallow foundations. Most Monterey city staff assume coastal no-frost conditions; if your lot is in a hillside or mountain area, mention frost depth in your permit application to avoid plan-review corrections. Hillside lots also trigger grading permits and erosion control plans under the California Building Code; a detached ADU on a sloped lot (greater than 25% grade) may require a geotechnical report showing slope stability and retaining wall design. These add 2-3 weeks to plan review and $1,500–$3,000 to design costs.
Coastal Monterey properties may fall under California Coastal Commission jurisdiction (if the property is within the Coastal Zone). The City of Monterey's municipal boundary includes most of downtown and residential areas within the Coastal Zone. If your ADU is in a property within the Coastal Zone, you may need a Coastal Development Permit (CDP) in addition to the regular building permit. The CDP is a separate approval from the city's Planning Division; it reviews visual impact, public access, and consistency with the Coastal Act. ADUs are generally 'compatible with the character of the area,' so CDPs for ADUs are often approved ministerially (like building permits), but the timeline adds 2-4 weeks. Check with Monterey's Planning Department or the Coastal Commission's GIS to verify if your lot is within the Coastal Zone. If it is, submit the CDP application concurrently with your building permit; the two can proceed in parallel, though permit issuance is contingent on CDP approval.
Monterey's soil is mostly granitic (sandy loam) near downtown and coastal areas, with some clay and silt in lower elevations. Expansive soils are not a widespread concern in Monterey city proper (they are more common in the inland Central Valley). However, properties near bay-adjacent areas or older developed zones may have infill soils, bay mud, or made ground that requires a geotechnical evaluation. If your site has a high water table (near bay or tidal wetlands) or obvious fill material, request a soils report during design — this costs $1,000–$2,000 and prevents foundation issues. Monterey's Building Department does not always require soils reports for ADUs, but if your site is visibly problematic (muddy, subsiding, adjacent to creeks), it's prudent to order one. A soils engineer will recommend foundation type, depth, and any special drainage measures. Concrete slabs in Monterey typically rest on 4 inches of gravel base (no special requirements in non-frost coastal zones), but if the lot is wet or sloped, you may need perimeter drains or a stemwall foundation instead of a slab. Planning ahead prevents post-permit discoveries and costly redesigns.
City of Monterey City Hall, 580 Pacific Street, Monterey, CA 93940
Phone: (831) 646-3700 | https://www.monterey.org/residents/building-planning
Monday–Friday, 8 AM–5 PM (verify online or by phone before visiting)
Common questions
Do I have to live in the primary dwelling while renting out the ADU?
No. AB 671 eliminated the owner-occupancy requirement effective January 2022. You can own the property as an investment, live elsewhere, and rent both the primary dwelling and ADU. However, if you are a non-owner occupant, you must ensure the primary dwelling and ADU are legally distinct and separately metered for utilities (Monterey requires separate water and sewer meters for detached ADUs even if both are rented). Some lenders have ADU-specific loan programs that assume owner occupancy; confirm with your lender before finalizing design if you plan to refinance.
What is a junior ADU, and can I build one in Monterey?
A junior ADU is a smaller accessory dwelling unit (up to 500 sq ft, or up to 25% larger if needed for ingress/egress and utilities) carved out of an existing dwelling structure (typically a garage, basement, or ADU-within-ADU). Junior ADUs can share utilities with the primary dwelling and require no separate water meter or electrical service. Monterey allows junior ADUs under California AB 2406 (state law 2018). They are faster to permit (30-day timeline instead of 60), lower cost ($4,000–$6,000 in permits), and simpler to build. If your garage is large enough, a junior ADU conversion is often the cheapest path to a second unit.
How much does it cost to permit and build an ADU in Monterey?
Permit and plan-review fees typically run $5,000–$12,000, depending on ADU size and complexity (detached, garage conversion, above-garage, or junior ADU). Construction costs vary widely: a 1,000 sq ft detached ADU in Monterey runs $400–$600 per sq ft in labor and materials (coastal Monterey is expensive), so $400,000–$600,000 total. A garage conversion costs $200,000–$350,000 (lower because you are reusing the structure). Utility connections (separate water meter, sewer lateral, electrical) add $3,000–$6,000. Sprinkler systems (if required for single-egress design) add $4,000–$6,000. Budget $450,000–$650,000 total for a detached ADU, $250,000–$400,000 for a garage conversion.
What is the timeline from permit to move-in?
Permit approval (design through stamped permit): 4-7 weeks for detached ADUs, 3-5 weeks for garage conversions, assuming plans are complete and correct. Construction (from permit issuance to final inspection): 12-18 weeks for detached new-construction, 8-14 weeks for garage conversion, depending on contractor availability and inspection schedules. Total calendar time: 16-25 weeks (4-6 months) from completed design to occupancy. Factor in 2-4 additional weeks if your property is in the Coastal Zone (Coastal Development Permit required) or if the lot is sloped (grading plan required).
Can I get a pre-approved ADU plan to speed up permitting?
California SB 9 (2021) and subsequent state laws allow pre-approved ADU designs that can be fast-tracked. The state HCD (Department of Housing and Community Development) maintains a list of pre-approved plans on its website. If your ADU matches a state pre-approved plan exactly (same footprint, same utilities, same egress), Monterey may issue a permit within 30 days without plan review (ministerial issuance). However, pre-approved plans are limited (few match real lot conditions), and Monterey's site-specific requirements (setbacks, utilities, slopes) often force customization. It's worth checking the HCD list, but most Monterey applicants end up customizing designs for their specific lot.
Do I need a separate electrical panel for the ADU, or can I tie into the primary dwelling's panel?
For detached ADUs, you need either a second service entrance (200-amp, separate meter to PG&E) or a sub-panel fed from the primary dwelling's service via a heavy-gauge wire. A second service entrance is simpler (no calculation of combined load), but more expensive ($2,500–$4,000). A sub-panel is cheaper ($1,200–$2,000) but requires load-calculation documentation showing the primary service has capacity. Monterey's plan review will ask for electrical one-line diagram showing the arrangement. For garage conversions and junior ADUs using shared utilities, you can upgrade the primary panel and run a sub-panel to the ADU (more economical because no second meter). Consult with a licensed electrician; they will know Monterey's PG&E interconnection rules.
If I convert my garage to a junior ADU and lose parking, can Monterey force me to provide a second parking space?
No. AB 671 explicitly prohibits Monterey from requiring off-street parking for ADUs in single-family residential zones. If you convert a garage to a junior ADU and lose the garage parking, you do not have to provide a replacement space. However, if your primary dwelling's building permit originally required two parking spaces (rare in Monterey, which has one-space minimums), and you lose one to the ADU, the primary dwelling is now under-parked. Most Monterey lots have driveway space for tandem (head-to-tail) parking; the city will accept this as a workaround. If your lot has no driveway, you can request a parking waiver, which Monterey must approve under AB 671.
What happens if my property is in a historic district or has an architectural-review requirement?
Monterey has multiple overlay districts and historic areas (Historic Old Town, Pacific Grove historic neighborhoods, Cannery Row district). If your property is in a historic district, you still need an ADU permit, but you may also need Historic District approval from the Planning Department. However, AB 671 prohibits architectural review that 'delays or prevents' ADU approval. Monterey's Planning staff are trained to process historic-district ADU applications on a fast-track (often 2-3 weeks) as 'compatible infill.' The ADU must not drastically alter the primary dwelling's front facade or roofline, but side/rear additions are typically approved. The state law overrides purely aesthetic objections. If the Planning Department denies your ADU on historic-district grounds, you can appeal to the State Housing and Community Development Department; very few denials survive scrutiny.
Can I be owner-builder for my ADU permit, or do I need a general contractor?
California Business and Professions Code Section 7044 allows owner-builders to permit and construct dwelling units on their own property, but with limits: electrical work requires a licensed electrician, plumbing requires a licensed plumber. You (the owner) can handle framing, exterior, finishes, and site work yourself, but must hire licensed subs for electrical, plumbing, and HVAC. Monterey's Building Department will issue the permit to you as owner-builder if you sign the application; you'll pull permits for the licensed trades (electrical, plumbing, mechanical) separately. Owner-builder status does not waive inspections — every trade inspection applies, plus framing, drywall, insulation, final walkthrough. It does save contractor markup (10-20% of labor/materials), but increases your liability. If anything goes wrong, you are responsible for corrections. Most Monterey ADU owners use a general contractor (simpler, turnkey), but owner-builder is allowed.
What happens if I disagree with Monterey's permit denial or plan-review comments?
If the city denies your ADU permit citing state law (e.g., 'property is too small for detached ADU'), you have the right to appeal to the city's Planning Commission or City Council within 10-15 days (check Monterey's appeal deadline). If you believe Monterey incorrectly applied AB 671 or other state law, you can also escalate to the State Attorney General's office or file a writ of mandate in Superior Court. Most disagreements are resolved via phone call with the city's ADU coordinator; misunderstandings about lot size, setbacks, or utility availability are usually clarified quickly. If you receive a denial and believe it conflicts with state law, contact the California Housing and Community Development Department (HCD) for informal guidance before appealing formally. The state law is very clear on ADU rights; Monterey is generally compliant, but errors happen.