What happens if you skip the permit (and you needed one)
- Building Department stop-work order: $500–$1,500 fine per day of unpermitted work, plus immediate reversal or demolition order if the unit is occupiable.
- Permit fees double on re-pull after discovery: you'll pay the original permit fee again plus a 'permit violation' surcharge of $1,000–$3,000.
- Title report and future sale blocked: unpermitted ADUs require Mello-Roos disclosure on resale or cannot be listed; lenders and title companies will refuse refinance until permit is retroactive or work is removed.
- Neighbor complaint to Building Department triggers code enforcement: typical enforcement timeline is 30–60 days, and fines escalate to $2,500–$5,000 for continued violation.
Redwood City ADU permits — the key details
California Government Code 65852.2 (amended by AB 671, AB 881, and SB 9) preempts local zoning and allows one ADU (or two in some cases) on any residential lot in Redwood City, regardless of local density limits or minimum lot size. The city cannot require a conditional-use permit, density reduction, or parking if the ADU is under 750 square feet and shares utilities or is attached to the primary residence. However, Redwood City's ADU ordinance still requires a full building permit and a 60-day maximum plan review per AB 671. The city must apply the California Residential Code (2022 edition) for ADU egress (IRC R310), electrical (NEC 2023), plumbing (Uniform Plumbing Code 2023), and fire separation if the ADU is attached. Detached ADUs must meet foundation and seismic requirements under IRC R401–R408 for the local soil type. In Redwood City's coastal zone (San Mateo County coastal segment), you also answer to California Coastal Commission standards, which may require an additional Coastal Development Permit if your lot is within 1,000 feet of the shoreline or in an environmentally sensitive area.
The most common reason Redwood City rejects ADU applications is incomplete utility separation and sewer-capacity documentation. The city requires a formal sewer-connection study (typically $500–$1,200 from a civil engineer) proving that the primary residence's existing sewer line can handle the ADU's wastewater. If the primary line is a 4-inch Clay tile from 1950, it may not be. You must also show a separate water meter or a sub-metering setup; the city will not approve a 'shared' meter. If the primary residence and ADU share a single meter, your plan will be marked 'revise and resubmit.' Additionally, if the combined square footage of the primary residence and ADU exceeds 5,000 square feet, Redwood City's Fire Code (California Fire Code 2022) triggers a sprinkler requirement for the entire lot under Section 903.3. Many homeowners find out mid-review that their 2,500 sq ft home plus a 2,600 sq ft ADU now require a $12,000–$18,000 fire-sprinkler system; the sprinkler system itself then becomes a separate permit and adds 3–4 weeks to the review.
Redwood City allows owner-builders for ADU construction under California Business & Professions Code § 7044, meaning you can pull the permit in your name and do non-trade work (framing, drywall, painting, landscaping). However, electrical work must be performed by a California-licensed electrician (C-10 general or specialty), plumbing by a state-licensed plumber (A license), and HVAC by an HVAC contractor (C-20). Final electrical inspection requires a state-issued Permit to Operate form signed by the electrician; the city Building Department will not sign off without it. This is a critical detail many owner-builders miss — the electrical contractor must obtain a separate state license (online filing, ~$100) before they can pull sub-permits. The same applies to plumbing if the ADU has a kitchen or bathroom with hot water lines. Gas work is also trade-restricted (C-16 Gas Fitter). If you hire an unlicensed worker, the city will issue a stop-work order, remove the work, and require re-inspection at your cost.
Redwood City's plan review timeline is capped at 60 days per AB 671, but the clock resets each time the city issues 'revise and resubmit' comments. Initial review comments typically come at day 21–28; you then have 14 days to respond. If your response is incomplete, the city resets the 60-day clock. In practice, expect 8–14 weeks from permit application to approval. The city uses an online portal (integrated with Accela software) where you can upload revised drawings and track comments in real time. Once approved, the permit is valid for 180 days; you must commence work within that window or pull a permit extension ($100–$300). Inspections are sequential: foundation/footing (before concrete pour), framing (before sheathing), rough electrical/plumbing/HVAC (before drywall), insulation and drywall, final mechanical and electrical, and final building. Each inspection is 24-hour notice; the city inspector is typically available the next business day but does not inspect on weekends or city holidays.
Total permit and plan-review fees for an ADU in Redwood City range from $5,000 to $15,000 depending on size and complexity. A 500 sq ft junior ADU garage conversion typically costs $4,500–$6,500 in permit fees (Building Permit ~$1,200, Plan Review ~$1,800, Electrical Permit ~$400, Plumbing Permit ~$600, Planning Review ~$600). A 800 sq ft detached ADU with new utilities runs $8,000–$12,000 (permits $3,000, plan review $2,500, sewer study $1,000, electrical and plumbing combined $1,800). If sprinklers are triggered, add $500–$1,500 for the sprinkler permit alone. Coastal Development Permits (if applicable) add $1,500–$3,000 and another 6–8 weeks. The city accepts checks, credit cards, and online ACH transfer via the Accela portal. There is no expedite fee for ADUs, but you can pay for preliminary plan review (non-binding feedback) before formal submission for ~$300–$500; this often saves time by catching setback or utility issues early.
Three Redwood City accessory dwelling unit (adu) scenarios
State law vs. local code: how SB 9 and AB 671 override Redwood City zoning
California Government Code 65852.2 (amended repeatedly, most recently by AB 881 in 2021) allows one ADU and one JADU (junior ADU) on any single-family residential lot in the state, regardless of local zoning or minimum lot size. Redwood City cannot impose density reductions, conditional-use permits, lot-size waivers, or ADU-specific parking requirements on an ADU under 750 sq ft that is attached to the primary residence or shares utilities. This is a hard preemption: local code is void to the extent it conflicts. However, Redwood City can still enforce setback requirements (front 20 feet, side 5 feet, rear 5 feet) for detached ADUs per Government Code 65852.2(e), and it can require ADUs to meet California Building Code (Title 24) standards for egress, electrical, plumbing, and fire separation. Redwood City's ADU ordinance (adopted in 2018 and amended in 2022 to align with state law) acknowledges this and explicitly states that setbacks are enforced but owner-occupancy requirements are waived.
AB 671 (passed 2021) added a 60-day maximum plan-review timeline for ADU permits, effective immediately. If the city does not approve or deny an ADU permit application within 60 days, the permit is deemed approved. However, this clock resets each time the city issues a request for more information (RFI). In practice, Redwood City's Planning and Building Departments coordinate on ADU reviews, and most are issued at 6–8 weeks because the first RFI typically comes at day 21. The city has been efficient at ADU reviews because staff has developed template checklists for utility separation, egress, and fire-separation. Some Bay Area cities (Palo Alto, Mountain View) use pre-approved ADU plan sets that bypass this review entirely, reducing timeline to 1–2 weeks for permit issuance. Redwood City does not yet offer pre-approved plans, so all ADUs go through full plan review.
AB 881 (passed 2021) added a second ADU (one JADU or standard ADU) per lot if the primary residence is not owner-occupied or if the primary is an existing apartment building. This is rarely used in Redwood City because most ADU applicants own and occupy the primary residence. However, if you own a rental house and want to add two ADUs, you may be eligible. The second ADU must follow the same state-law waivers (no parking, no density reduction, no owner-occupancy), but local setbacks still apply. Redwood City has not yet clarified whether it interprets 'two ADUs' as one standard ADU + one junior ADU, or two standard ADUs. Email the Planning Department to confirm for your specific lot.
Utility separation, fire sprinklers, and why sewer capacity kills applications
Redwood City requires an 'as-built' or engineer's certification that the existing sewer lateral serving the primary residence has capacity to handle both the main house and the ADU. For a typical Bay Area 4-inch PVC or cast-iron sewer line from the 1970s–2000s, capacity is not an issue; design flow is ~400 gallons per day for residential use, and an ADU adds ~100 gallons per day. However, if the primary residence has a 3-inch clay tile line from 1950 or earlier, or if it shows signs of root intrusion or collapse (common in the Bay foothills), the city will require a sewer-camera inspection ($600–$1,200) and may mandate sewer-line replacement (upsized or re-laid) before ADU approval. Sewer replacement can run $8,000–$20,000 and is often a deal-breaker. The city issues a stop-work order if you proceed without proving sewer capacity. Many applicants discover this issue only at plan review, forcing them to either abandon the ADU or spend months and thousands on a sewer upgrade that was not in the original budget.
Water metering is similarly strict. Redwood City requires a separate water meter for the ADU — either a completely new meter from the main line (if the city's water line is accessible near the rear lot) or a sub-meter installed downstream of the main meter. A separate meter costs $500–$1,500 (city installation fee + plumber labor). A sub-meter (mechanical meter placed in the supply line) costs $200–$400 but requires annual reading and is less preferred by the city because it creates billing disputes. The city will not approve 'shared' metering under any circumstance, even if you use a cost-split agreement with the tenant. This rule is tied to state water-conservation standards (California Code Title 20) and applies statewide. Redwood City's Water Department also enforces a local low-income-water-conservation surcharge for properties with two units, but this is a post-occupancy fee (~$50/year) and not a permit issue.
Fire sprinklers are the third utility killer. California Fire Code Section 903.3 requires fire sprinklers in one- and two-family residences (including ADUs) if the combined square footage of the primary residence plus the ADU exceeds 5,000 square feet. For a 2,600 sq ft house plus a 2,500 sq ft ADU, sprinklers are mandatory. Redwood City enforces this rule strictly. A full residential fire-sprinkler system costs $8,000–$18,000 (design, materials, installation, inspection) and adds 3–4 weeks to the project timeline because the sprinkler contractor must pull a separate permit and coordinate with the Building Department. Many homeowners realize this only mid-review and decide to downsize the ADU or abandon the project. Conversely, if your primary residence is under 3,500 sq ft and you cap the ADU at 1,500 sq ft, you're still under the 5,000 threshold and can skip sprinklers — this is a common strategy to reduce costs.
Redwood City City Hall, 1017 Middlefield Road, Redwood City, CA 94063
Phone: (650) 780-7000 (main line; ask for Building or Planning Department) | https://www.redwoodcity.org/departments/planning-and-building-department (Accela-based online permit portal; login required to check status and upload documents)
Monday–Friday, 8:00 AM–5:00 PM (closed city holidays; verify holidays on city website)
Common questions
Can I build a detached ADU if my lot is only 0.25 acres?
Yes. State law (Government Code 65852.2) does not impose a minimum lot size for ADUs. Redwood City can enforce setback requirements (5 feet rear, 5 feet side, 20 feet front for detached ADUs), so you must ensure the ADU fits within those setbacks. A 0.25-acre lot (about 108 x 108 feet) will typically accommodate a detached 600–800 sq ft ADU in the rear with 5-foot side and rear setbacks. However, you must verify setbacks on your specific lot; the city's online tool (Parcel Lookup on the city website) shows lot dimensions and zoning overlays.
Do I need to hire an architect or can I use a template ADU plan?
You can use a template ADU plan if it is stamped by a California-licensed architect or engineer. Several vendors (e.g., ADU Builders, Bay ADU, ABODU) offer pre-stamped 500–800 sq ft plans for $1,000–$2,500. However, the plan must be customized to your site (roof pitch, foundation depth, solar orientation, existing utilities) by a local architect or engineer before submission to Redwood City. Customization typically costs $1,500–$3,000. Alternatively, you can hire a local architect from scratch for $2,500–$4,000. The city does not offer pre-approved plan sets, so some customization is always required.
If I am the owner-builder, do I have to be present at every inspection?
California Building Code does not require owner-builder presence at inspections, but Redwood City Building Department prefers it and will not clear a rough-electrical inspection without the electrical contractor present to discuss code compliance. For framing, drywall, and final inspections, the inspector can approve or reject work in the owner-builder's absence if the work is clearly documented and photos are on file. However, it is safer and faster to be present. If you hire a general contractor as your agent, they can represent you at inspections.
What if my sewer line is old and the city says it needs replacing before I can get the ADU permit?
The city will require a sewer-capacity letter from a civil engineer or plumber. If the engineer flags the line as undersized or failing, the city will issue an RFI (request for more information) asking you to either (1) replace the sewer lateral before permit approval, or (2) submit a structural repair plan (pipe bursting, spot repairs, or full replacement). Replacement typically costs $8,000–$20,000 and adds 4–8 weeks. You can negotiate with the city to allow the sewer work to be completed as a condition of occupancy (CO) rather than before permit issuance; this is discretionary. If you choose to proceed, budget for the sewer upgrade in your total project cost.
Does Redwood City require me to live in the primary residence if I build an ADU?
No. California state law (Government Code 65852.2) explicitly waives owner-occupancy requirements for ADUs. Redwood City's ADU ordinance confirms this: you can own a non-owner-occupied rental house and build an ADU on the lot without any restriction. You do not need to occupy either unit. However, if you rent out both the primary residence and the ADU, you will be subject to Redwood City's rental-licensing requirements and are responsible for property-tax reassessment (the ADU may trigger a marginal increase in assessed value).
Is there a permit timeline guarantee, or can the city delay indefinitely?
AB 671 mandates a 60-day decision timeline for ADU permits. If the city does not approve or deny within 60 days, the permit is deemed approved. However, the clock resets each time the city issues an RFI (request for information). In practice, the city typically issues one RFI at day 19–24, giving you 14 days to respond. If your response is complete, approval follows at day 50–60. If your response is incomplete, the 60-day clock resets. Redwood City's ADU reviews are efficient (most approve in 6–8 weeks), but coastal-zone ADUs requiring a Coastal Development Permit may add 4–6 weeks because the CDP timeline is separate and is not subject to the 60-day rule.
What is the difference between a junior ADU and a standard ADU, and which is cheaper to permit?
A junior ADU (JADU) is capped at 500 sq ft (including lofts and mezzanines) and must share at least one major utility (water, sewer, or electric) with the primary residence or use a sub-meter. A standard ADU can be up to 800–1,000 sq ft (varies by local code) and can have separate utilities. Permit fees are similar ($5,000–$7,000 for either), but a JADU typically has lower plan-review costs because it is simpler (often a garage conversion with fewer new systems). If you are converting a garage, a JADU is often faster and slightly cheaper overall. If you are building new, a standard ADU gives you more square footage and may not cost significantly more in permits, though construction costs will be higher.
If my ADU is in the Coastal Zone, what extra permits or reviews do I need?
Redwood City is partly within the California Coastal Zone (the western 1 mile or so is subject to Coastal Commission jurisdiction). If your lot is within the Coastal Zone (visible on the city's zoning map), you must obtain a Coastal Development Permit (CDP) before building any ADU. The CDP is issued by the Redwood City Planning Department, not the Coastal Commission, but it enforces Coastal Act standards. For an ADU, the CDP is often categorically exempt under CEQA (no environmental review needed) and approved by the Director (4–6 weeks). You must submit a view-corridor analysis ($500–$800) and a geotechnical report if the site is in a landslide hazard zone (common in coastal foothills). Total added timeline: 4–6 weeks. Total added cost: $1,500–$3,000. If your lot is outside the Coastal Zone, no CDP is required.
Can I pull an ADU permit if I have an existing unpermitted structure on the lot?
Redwood City will not approve an ADU permit if there is an unpermitted habitable structure on the lot. The city will require you to either (1) obtain a retroactive permit for the unpermitted structure, or (2) demolish it. Retroactive permits for older structures can be expensive and time-consuming (often $2,000–$5,000 in fees and 4–8 weeks for plan review) because the city may require upgrades to current code (seismic bracing, electrical rewiring, sprinklers if triggered). If the unpermitted structure is an old shed or storage building, demolition is often cheaper. Disclose any unpermitted structures to the Building Department upfront; hiding them will result in a stop-work order and fines.
What happens after I get a Temporary Certificate of Occupancy (TCO) — can I let the tenant move in?
No. A TCO is an interim approval allowing partial occupancy (e.g., kitchen and bedroom are done, but final electrical is pending). A full Certificate of Occupancy (CO) is required for the tenant to legally move in. After final inspection, the city issues a CO, which is permanent unless code violations are found. The CO must be framed and posted on the property. Redwood City will not issue a CO until all utility sign-offs are complete (separate water meter, sewer connection, electrical permit card, HVAC inspection if required). Once the CO is issued, the ADU is legal and the city will not mandate further upgrades unless you violate code or add habitable space.