What happens if you skip the permit (and you needed one)
- Stop-work order issued by San Bruno Building Department; typical fine $500–$1,500 plus double permit fees when you finally pull it.
- Title company may flag unpermitted structure on resale; buyer lender refuses to close, or you're forced to disclose and eat a $30K-$80K price reduction.
- Insurance claim denial if fire or liability occurs in unpermitted ADU; homeowner's policy exclusion language is explicit.
- Refinance or HELOC blocked; lenders require clear title and code compliance; unpermitted ADU is material title defect in Bay Area market.
San Bruno ADU permits — the key details
San Bruno's ADU pathway is governed by two layers of law. The bottom layer is California Government Code 65852.2 (and its 2020 update AB 881), which sets a statewide floor — cities cannot ban ADUs, cannot require owner-occupancy, and cannot impose parking or lot-size restrictions beyond state minimums. The top layer is San Bruno's local ADU ordinance, which must comply with state law and fills in details like design review, utility submeter requirements, and inspection sequences. In practice, this means San Bruno cannot tell you 'no' on zoning grounds — but the City can (and will) require a complete building permit application, plan review, foundation and framing inspection, and utility coordination. IRC R310 (emergency egress from bedrooms) and IRC R401-R408 (foundation if detached) apply regardless of local ordinance. The state shot clock (60 days from complete application) is enforceable; San Bruno must issue or deny within that window.
Detached ADUs on small lots are the most common flash point. San Bruno allows detached ADUs in most residential zones, but state law sets the minimum setback at 4 feet from a rear or side property line (or whatever the primary dwelling's setback is, whichever is less restrictive). If your lot is 40 feet wide, a 12-foot-wide detached unit with 4-foot setbacks on both sides plus the main house is tight — but state law says San Bruno cannot require wider setbacks. The City will still require a survey or lot line certification, foundation design (if on separate footings), and clear utility separation (or submetered water and electric). Garage conversions are treated as ADUs under state law, so the same 60-day clock and no-owner-occupancy rule apply. Junior ADUs (unlawful rent rooms inside the primary dwelling, sharing kitchen) are exempt from San Bruno's parking and design review under state law, though plan review is still required.
Utility coordination is the second major hurdle. San Bruno requires either separate utility connections (separate water meter, electric panel, gas line if applicable) or submetered service. If you're converting an attached garage or adding an above-garage unit, the submetering cost is typically $2,000–$4,000 extra for water and electric; separate connections cost $5,000–$10,000 depending on distance to main panel and water entry. The City will not approve final occupancy without utility sign-off from PG&E (gas/electric) and the water district (typically San Bruno Water Company). This is not optional and often extends the timeline by 2-4 weeks if utilities need trench work or panel upgrades.
Foundation and structural design is mandatory for detached ADUs and new construction (like above-garage units on a second story). San Bruno will accept prescriptive-design ADU plans that comply with IRC R401 (shallow foundations, pier-and-beam, slab-on-grade), but if your lot has problematic soil (Bay Mud, clay, or steep slope), you'll need a geotechnical report and a structural engineer's stamp. Cost is $1,500–$3,000 for a soil report and $2,000–$5,000 for structural design. The plan must show frost depth (though San Bruno coastal is mostly non-critical for frost; interior slopes may require 12-18 inches), lateral bracing, and compliance with local seismic requirements (Bay Area is high seismic hazard). Plan review typically takes 3-4 weeks; resubmittals (common for ADUs on complex lots) can add 2-3 weeks.
Owner-builder is allowed under California Business & Professions Code § 7044, meaning you can pull a permit and manage your own ADU project. However, you must hire a licensed contractor (C-10 general or specialty license) or licensed electrician (C-10 can pull electrical, or C-6 licensed electrician required), and a licensed plumber for all water and drainage work. Many owner-builders contract the trades separately and manage scheduling themselves — this saves 15-25% on labor. San Bruno's Building Department accepts owner-builder applications; you'll sign as property owner and certify that you're doing the work yourself, then schedule inspections with the licensed trades in attendance. Typical timeline for an owner-builder detached ADU (800 sq ft) is 5-6 months from permit to certificate of occupancy; contractor-built is 4-5 months with higher labor cost.
Three San Bruno accessory dwelling unit (adu) scenarios
California state ADU law and how it overrides San Bruno's local code
San Bruno cannot enforce its own ADU restrictions if they conflict with state law. California Government Code Section 65852.2 (added 2017, updated by AB 881 in 2020) is a legal floor that every city in California must meet. The statute says: (1) cities must allow one ADU and one junior ADU per single-family residential lot, (2) cities cannot require owner-occupancy of the primary dwelling, (3) cities cannot impose parking requirements for ADUs, (4) cities cannot impose lot-size, lot-frontage, or setback restrictions stricter than those applied to the primary dwelling, (5) cities must process ADU permits on a ministerial basis (no discretionary conditions), and (6) cities must issue or deny within 60 days of a complete application. San Bruno's local ordinance is required to comply with these rules.
What this means in practice: if San Bruno's old code said 'ADUs only allowed in R-3 zones' or 'ADU owner must occupy primary residence,' those rules are unenforceable. If you apply for an ADU in any residential zone, San Bruno cannot deny it on zoning grounds. If you want to rent out the ADU while you live elsewhere, state law says San Bruno cannot require you to occupy the primary dwelling. If your neighborhood is walkable and near transit (true in most of San Bruno), state law says San Bruno cannot impose parking. Setbacks for the ADU cannot exceed the setbacks for the primary dwelling; if the main house is 10 feet from the rear line, the ADU must also be allowed at 10 feet (or the state minimum of 4 feet, whichever is less restrictive).
However — and this is critical — state law preemption does NOT eliminate the building permit process or structural safety requirements. San Bruno must still require you to pull a building permit, submit architectural and engineering plans, pass plan review (non-discretionary — staff applies code, doesn't use judgment), and complete all inspections. The 60-day clock is the time for plan review and decision, not for construction. You are still responsible for IRC compliance (egress, foundation, electrical, plumbing, fire safety), utility coordination, and site conditions (geotechnical reports if soil is problematic). State law fast-tracks the zoning and preliminary approval; it doesn't waive engineering.
Utility submeter requirements and separate connections in San Bruno
San Bruno requires that each ADU have independent utility service or submetered service — meaning the ADU cannot share a single water meter or electric panel with the primary dwelling. This is for billing purposes (if you rent the ADU, the tenant must pay their own utilities) and for code compliance (IRC R401 requires separate disconnects and isolation). For detached ADUs, separate connections are typical: new water meter (new service line from main, new meter box, $4,000–$8,000), new electric panel and service drop (or two-service split if panel is on shared wall, $3,000–$6,000), and separate gas meter if applicable ($1,500–$3,000). Total separate-connection cost: $8,000–$15,000. For garage conversions and above-garage units, submetering is cheaper: a water submeter installed on the existing service line ($800–$1,500), and an electric submeter or dedicated breaker circuit within the existing panel ($500–$1,200). Submetering total: $1,500–$3,500.
San Bruno's Building Department and the water company (San Bruno Water Company) and utility provider (PG&E) coordinate on these requirements. You must include utility plans in your permit application — show where the new meter(s) will be located, routing of lines, and any panel upgrades. PG&E and water company will then issue service agreements (1-2 weeks) and schedule connection work (2-4 weeks). This work is often on the critical path; delays in utility coordination can push your permit-to-occupancy timeline by 4-6 weeks. Plan ahead: contact PG&E and the water company early (even before you submit the permit application) to confirm service availability, line routing, and estimated cost. Many permittees are blindsided by a $12,000 utility bill because a new service drop requires trenching 200 feet through a neighbor's easement.
San Bruno City Hall, 567 El Camino Real, San Bruno, CA 94066
Phone: (650) 616-7055 or check city website for current number | https://www.sanbruno.ca.gov (search 'building permits' for online portal or application guidance)
Monday–Friday, 8:00 AM–5:00 PM (closed holidays; verify before visiting)
Common questions
Can I rent out an ADU if I don't live in the main house?
Yes. California AB 881 removed owner-occupancy requirements effective 2020. San Bruno cannot require you to occupy the primary dwelling; you can rent both the ADU and main house to tenants, or live in the ADU and rent the main house. State law is clear: owner-occupancy is not a condition of ADU approval. However, local rent control, landlord-tenant law, and property taxes still apply; consult a tax accountant about Prop 13 reassessment if you convert a single-family property to a rental ADU.
Do I need parking for an ADU in San Bruno?
No. California state law (Government Code 65852.2) waives parking requirements for ADUs. San Bruno cannot require you to build or reserve a parking space for the ADU. This applies even if your neighborhood is car-dependent — state law overrides local parking ordinances for ADUs. If your lot has existing parking and you want to keep it, that's fine; if not, you're still compliant.
What's the timeline from permit to move-in?
Typically 12-18 weeks for a detached ADU (longer if geotechnical or structural review is needed), 8-12 weeks for a garage conversion, and 14-20 weeks for an above-garage unit with second-story construction. San Bruno's 60-day plan review is part of this; the bulk of time is spent in construction and inspections. Owner-builder projects take slightly longer due to inspection scheduling around trade availability; contractor-built projects are more predictable.
Do I need a variance or conditional-use permit for an ADU in San Bruno?
No. State law requires ADU approvals to be 'ministerial' — meaning San Bruno staff applies the code and approves it without discretion or conditions. No planning commission hearing, no variance, no conditional-use permit, no design review (unless the lot is in a historic district, then design review may apply but cannot be used to deny the ADU). This is a major advantage over pre-2020 ADU law in some cities.
What if my lot is very small (e.g., 2,500 sq ft)?
State law allows ADUs on any residentially zoned lot, regardless of size. The only restriction is setbacks (state minimum 4 feet from property line, or match the primary dwelling's setback if it's wider — but San Bruno cannot require wider setbacks). A 2,500 sq ft lot in San Bruno can hold a small detached ADU (400-500 sq ft) if setbacks work. Bring a survey to your pre-application meeting with the Building Department to confirm feasibility; they cannot deny it on lot-size grounds, but they can verify setback geometry.
Are impact fees and connection fees part of the permit cost?
Yes. San Bruno's total ADU permit cost includes building permit ($2,000–$3,500), plan review ($1,500–$2,500), and development impact fees (varies by use; estimate $1,500–$3,000 for ADU). Utility connection fees (separate from permit fees) are paid to PG&E and San Bruno Water Company, not to the City. Total city fees are typically $5,000–$8,000; utility connections are $6,000–$12,000 additional. Some ADU-friendly jurisdictions waive impact fees for ADUs; confirm with San Bruno whether they offer any ADU waivers.
Can I pull a permit for an ADU myself as an owner-builder?
Yes. California B&P Code § 7044 allows owner-builders to pull residential permits. You sign the permit application as the property owner/builder; you are responsible for hiring licensed contractors for electrical (C-6 or C-10), plumbing (C-36), HVAC (C-20), and general work (C-10 or specialty). San Bruno's Building Department will assign a plan-review code official and schedule inspections with you. Owner-builder saves money but requires more coordination; expect to spend 10-15 hours per week managing trades and scheduling inspections.
What happens if I build an ADU without a permit?
San Bruno's Building Department can issue a stop-work order ($500–$1,500 fine), require you to pull a permit retroactively (double fees, $8,000–$12,000), and demand structural proof that the ADU meets code (often requires engineer evaluation, $2,000–$4,000). If you sell the property without disclosing the unpermitted ADU, the title company and buyer's lender will catch it (via permit history check or physical inspection); you'll either be forced to demolish it, bring it up to code (with all permit fees and inspections), or accept a 15-30% price reduction on resale. Insurance will deny claims for fire or liability in the unpermitted unit.
Do I need to file any paperwork with the county assessor after the ADU is permitted?
Yes. Once the ADU receives a certificate of occupancy from San Bruno, notify the San Mateo County Assessor's Office (where San Bruno is located). The assessor will reassess your property value (likely increasing it 10-25% depending on ADU size and rental income), and you'll see a tax increase on your next property tax bill. Some jurisdictions allow Prop 13 deferral for ADUs under certain conditions; consult a tax professional before starting the project if you're concerned about reassessment.
What's the difference between a junior ADU and a standard ADU in San Bruno?
A junior ADU is a unit created within the primary dwelling (or garage conversion) that shares kitchen facilities with the main house — meaning it has a sink, refrigerator, and dining area, but no full stove or cooking range, so it's not technically a separate 'living unit' under zoning law. A standard ADU is a complete, self-contained dwelling with a separate kitchen (stove, refrigerator, sink). State law allows both; junior ADUs are exempt from parking and setback rules, and fast-track approval in some jurisdictions. San Bruno permits both, but a junior ADU application may move through plan review faster (2-3 weeks vs. 3-4 weeks for a standard ADU) because there are fewer structural and utility complexities. Rental rates for junior ADUs are typically 20-30% lower than for standard ADUs.