Do I need a permit for an Accessory Dwelling Unit (ADU) in
Martinez, California?

Martinez ADU permits — the key details

State law owns ADU zoning in California. AB 881 (effective 2020) and SB 9 (effective 2022) stripped cities of authority to ban ADUs or impose conditions that effectively block them. In Martinez, this means you cannot be denied a permit solely because your lot is zoned single-family residential, or because local voters dislike ADUs, or because your neighbors object. The city must process your ADU application within 60 days of a complete filing (per AB 671, Government Code 65852.2(d)). That said, Martinez can still enforce legitimate health-and-safety codes: egress windows (IRC R310), utilities (code-compliant separately metered or sub-metered), parking (the city has largely waived parking for ADUs under 750 sq ft if certain conditions are met), and setbacks (state law allows reduced setbacks for accessory units). If your proposal triggers environmental review (rare for ADUs), or if it sits in a habitat-sensitive area, the 60-day clock pauses, and you could see 90–120 total days. The key is filing a complete application: site plan showing setbacks and lot coverage, floor plan with egress, utility layout, and proof of separate water/sewer/electrical service or sub-meter arrangement.

Martinez's local ADU ordinance and pre-approved plans. The city published its ADU rules (check the Martinez Planning Division website for the latest Municipal Code chapter or ADU fact sheet). Importantly, if your ADU matches California's state-approved 'ADU Program' plans (available free from the Adaptive Reuse of Housing for Accessory Dwelling Units project or HCD), Martinez cannot reject it on design or setback grounds — it must be deemed ministerial, and you get the fastest possible review (often 2–3 weeks for plan check). Pre-approved plans are available for detached ADUs (400–800 sq ft), garage conversions, and junior ADUs. If you do NOT use a state-blessed plan, your proposal goes to standard plan review, where the city's planner checks setbacks, building coverage, parking, and egress. This adds 4–8 weeks. Owner-builders can file for ADU permits under California Business & Professions Code § 7044, but electrical work, plumbing, and mechanical must be done by licensed contractors or the property owner themselves (only if owner is a licensed electrician/plumber — rare). Most homeowners hire a contractor for these trades.

Setbacks, lot size, and the 'accessory' rule. Martinez uses a tiered setback table in its local ordinance. For detached ADUs, typical minimums are 5 feet from rear property line and 5 feet from side setback (lower than single-family house rules). For garage conversions or ADUs above a garage, setbacks are relaxed further — often zero feet if the structure already exists. There is NO minimum lot size mandated by state law, though the building site must be large enough to accommodate the ADU footprint, parking (if required), and utilities. Contra Costa County's soil is mixed: coastal Martinez has compacted bay silt and sand; inland hills have granitic and clayey soils. Detached ADUs require a foundation (IRC R401–R408): typically slab-on-grade with 12-inch footings in stable soils, or pilings in expansive clay. Your engineer or contractor will size it based on a soil report (often $500–$1,500). One surprise: AB 881 prevents the city from requiring the ADU lot to be larger than the main house lot — a state-law floor on local zoning tyranny. Parking is complex. Martinez MAY require one off-street parking space for an ADU up to 750 sq ft if the unit is within a half-mile of transit or a TOD zone; zero spaces if farther or in a very-low-income area. But many cities (and Martinez increasingly) have waived ADU parking entirely. Check the latest city planning memo or call the building department to confirm the current parking rule — it changes quarterly as state law updates.

Utilities, egress, and inspection. Every ADU must have code-compliant egress: one operable window per bedroom (min. 5 sq ft, 24-inch width/height, sill ≤44 inches — IRC R310.1) or a second door. Garage conversions must trap the garage egress door behind a 1-hour fire wall, so a separate entry door is usually mandatory. Utilities must be sub-metered or separately metered to the ADU so that water, sewer, and electric are billed individually (or to you as the property owner separately). This is not optional — it's a state law trigger (AB 68) and a local requirement in Martinez. You'll file a utility letter from the property owner and the water/sewer district (East Bay Municipal Utility District for Martinez) confirming the sub-meter or separate connection plan. Electrical must be on a separate breaker panel (not shared with main house). Once your permit is issued, inspections follow the standard sequence: foundation, framing, rough trades (electrical, plumbing, HVAC), insulation/drywall, final building, and utility sign-off. For a 600-sq-ft garage ADU, expect 5–7 inspections over 8–12 weeks. For a detached new-build, add 1–2 inspections (grading, soils compaction). The city provides an inspection checklist with the permit; you schedule each through the online portal or phone.

Timeline, costs, and owner-occupancy. A typical ADU permit in Martinez costs $3,000–$15,000 depending on the project scope. This breaks down as: base permit fee (flat ~$500–$800), plan-review fee (tiered on square footage, ~$1,000–$3,000), and impact/mitigation fees (rarely applied to ADUs, but can add $1,000–$5,000 if traffic or school impacts are flagged). Pre-approved plans reduce plan review time and fee by ~40%. Total timeline from application to construction start: 4–6 weeks for a pre-approved garage ADU, 8–12 weeks for a custom design. California's AB 68 also requires ADU owner-occupancy for the main house in certain circumstances — specifically, if you're creating a junior ADU (smaller, inside the main dwelling), the owner MUST occupy the main house. For detached ADUs, there is NO owner-occupancy mandate in state law (though local ordinance can require it; check Martinez's latest rules). If you plan to rent both the main house and ADU to tenants, a detached unit is safer legally. Your city building contact is the Community Development Department; they host an online permit portal for applications and inspection scheduling. Processing times are publishing: 60 days for ministerial (pre-approved plan) ADUs, 90–120 days for design-review ADUs.

Three Martinez accessory dwelling unit (adu) scenarios

AB 881 and SB 9: How California state law overrides Martinez zoning

In 2020, California Assembly Bill 881 went into effect, stripping local governments of the power to ban accessory dwelling units in single-family zones. Before AB 881, Martinez could (and did) restrict ADUs to owner-occupied properties, require conditional-use permits, impose lot-size minimums, or simply deny permits. Post-AB 881, the city cannot do any of this for detached ADUs or garage conversions under 800 sq ft (or 850 sq ft if owner-occupied). SB 9 (effective 2022) extended these protections: you can split a single-family lot into two parcels, each with an ADU, without subdividing (if you occupy one unit). In Martinez, this means a property owner can build a detached ADU on a 0.25-acre lot — something the local zoning code would have forbidden five years ago.

What Martinez CAN still regulate: egress safety (windows per IRC R310), utilities (separate metering per AB 68), parking (now minimal or waived), setbacks (state-law minimums are low enough that most lots qualify), and building/fire code compliance (standard building department review). The city cannot apply 'design review' to an ADU that matches a state-approved plan; it must approve ministerially. Ministerial means the building department checks the box that the plan meets code, no discretion, no delays. However, if your ADU is over 800 sq ft, or sits on a lot under 2,500 sq ft, or triggers environmental thresholds (rare), design review may apply. The 60-day clock (AB 671) resets if the city deems your application incomplete; if it is complete, the city must issue or deny within 60 days. This has forced Martinez to streamline — the city now has a dedicated ADU intake form and a staff planner to ensure completeness checks are accurate.

On the ground in Martinez, this manifests in streamlined processing. The city's website now features a one-page ADU fact sheet (check the Planning Division page) listing what's needed: completed application, site plan, floor plan, proof of separate utilities, and owner ID. No conditional-use permit, no variance, no vesting tentative map. If you bring complete paperwork and use a state-blessed plan, you could have approval in 2–3 weeks. The practical effect: ADU applications in Martinez are moving faster than they did in 2018–2019, and the city is approving them at near 100% (only rejections are for incomplete filings or code violations like insufficient egress).

Utilities, sub-metering, and why separate water/sewer is non-negotiable

AB 68 (effective 2022) mandated that every ADU have separately metered utilities — water, sewer, and electric — OR be sub-metered within a single meter. The law was written to protect tenants from inflated utility bills (where a landlord bills a tenant for 'their share' of water without a meter) and to enable property-tax assessment (assessor offices tax ADUs based on separate utility service). In Martinez, this means you cannot share a single water meter between the main house and ADU. You must either (1) install a separate water meter through East Bay Municipal Utility District (EBMUD), or (2) install a sub-meter within your property's main meter (permitted, but sub-meters have accuracy issues and are less favored). EBMUD charges roughly $2,000–$3,000 for a new meter installation (one-time; then ~$40–$80/month service charge for the ADU). Sewer is bundled with water in most Bay Area utilities; you coordinate a single call to EBMUD, and they install one meter for both water and sewer. Electrical is simpler: you run a separate breaker panel in your main house and sub-meter the ADU, OR have the utility (Pacific Gas & Electric, PG&E) install a separate meter (cheaper, ~$500–$1,000 one-time; then the utility bills the ADU tenant directly).

On a garage conversion (Scenario B), you likely already have a water line running to the garage (for a hose or carwash). Tie-in the new ADU kitchen sink and bathroom to that line, have EBMUD install the sub-meter, and you're done — no trenching. On a detached ADU (Scenario A), you may need to trench from the main water meter to the ADU; budget $1,500–$2,500 for that if the distance is more than 50 feet. Plan-check staff will ask to see a utility letter from the plumber stating 'separate meter planned' or 'sub-meter location shown on drawing.' If you don't address utilities in your permit application, the city will issue a plan-review comment ('Provide separate utility plan') and pause the 60-day clock. This is the #1 reason for delays. Applicants who bring complete utility letters (signed by EBMUD, PG&E, or a licensed plumber) get through plan check 2–3 weeks faster. Some property owners try to avoid sub-metering ('We'll just share and bill separately') — do not do this. It's a code violation, and code enforcement can force removal if a complaint arises.

For owner-builders, note that California plumbing contractor licensing (B&P Code § 7044) allows property owners to do their own plumbing work if they obtain the permit and sign as the 'responsible managing employee.' However, the connection to EBMUD's main must be done by a licensed plumber or EBMUD contractor; you cannot do that yourself. Electrical is similar: you can do wiring inside your ADU if you pull a permit under your name and pass city inspections, but the meter install and PG&E connection must be done by PG&E or a licensed electrician. Most homeowners outsource to avoid the hassle; a licensed electrician charges ~$800–$1,200 for a full ADU electrical rough-in, plan-check sign-off, and meter coordination.

Common questions