ADU Permits in Los Altos

I’ve pulled permits in a dozen Bay Area cities, and I have never seen anything like what Los Altos does on its own fee schedule. The City of Los Altos’s Development Services fee schedule for fiscal year 2025 to 2026 lists the ADU building permit fee, the ADU plan check fee, and the ADU electrical, mechanical, or plumbing permit fee at $0.00 each. Not a discount. Zero.

I checked that twice before writing this: once myself against the published PDF, and a second time by having someone independently pull the same three line items straight off the document. Both times, same result. Los Altos isn’t free to build in overall, the city’s construction tax and any outside utility fees still apply, but the specific permit and plan check charges that most California cities bill you a few thousand dollars for are genuinely, officially zero here.

What Changed for Los Altos ADU Permits in 2026

Start with the state, because that’s where the biggest structural changes landed. Four bills, AB 462, AB 1154, SB 543, and a 2025 amendment to SB 9, took effect January 1, 2026, and all four apply in Los Altos the same as everywhere else in California. SB 543 shifts ADU size measurement to interior livable space and puts a 15-day clock on completeness determinations, after which an incomplete application is deemed complete by default if the city misses it. AB 1154 narrows JADU owner-occupancy so it only kicks in when the JADU shares a bathroom with the main house. AB 462 adds a firm 60-day clock for Coastal Development Permits tied to an ADU, though that one matters more in coastal cities than here. The SB 9 amendment gives California’s Housing and Community Development department real enforcement teeth: if a city’s ADU ordinance doesn’t comply with state law and the city doesn’t fix it after notice, HCD can void the noncompliant parts and state standards apply instead.

That last piece is live in Los Altos right now, not theoretical. HCD sent the City of Los Altos an ADU ordinance technical assistance letter dated December 5, 2025, flagging that the city’s ordinance needs updates to line up with current law, including how third parties like homeowners associations get treated in the approval process. I wasn’t able to pull the full letter text (it returned an access error when I tried), so I’m only citing what HCD’s letter listing confirms exists, not its detailed contents. Separately, I checked the city’s own published guidance and its JADU owner-occupancy language still reads as a blanket requirement, without AB 1154’s narrower bathroom-sharing condition built in. If that hasn’t been updated by the time you’re reading this, the state’s narrower rule controls regardless of what the older city page says. Confirm current status with the Building Division directly.

Locally, beyond the July 1, 2025 fee schedule and the December 2025 HCD letter, I didn’t find a separate Los Altos-specific ADU process change with its own 2026 effective date. If the city adopts ordinance amendments in response to the HCD letter, this page needs an update, and I’ll flag it when that happens.

How the Los Altos ADU Permit Process Works

The Building Division handles ADU plan check and permit issuance. Custom ADU applications, standard site-specific submittals, and pre-approved plan submittals all go the same way: emailed as PDFs to bldpermit@losaltosca.gov, with larger file sets sent through a dropbox link. The city stopped taking hard copies at City Hall. There’s no dedicated online portal for the ADU plan check submittal itself, that part is email-based, though the city runs an eTRAKiT portal at trakit.losaltosca.gov for simpler permit types and for tracking status, paying fees, and scheduling inspections once a permit exists.

Once you submit, the city’s own pages describe intake and completeness review running a handful of business days, up to 5 business days per its permit submittal process page, with plan processing described as 2 to 4 business days on the Building Division’s own page. Call it roughly a business week either way. From there the application moves into plan check, and if corrections come back you get a comment letter and resubmit with a response letter, delta-numbered revised plans, and the same format as your original set.

A few mechanical details matter more than they sound like they should. Los Altos is a combination jurisdiction, which means all rough inspections, framing, electrical, plumbing, and mechanical, happen at the same inspection visit. No partial inspections, no phasing. And an application that sits unpursued gets deemed abandoned after 180 days, so don’t let a submittal go quiet for half a year and expect it to still be alive.

One utility step is genuinely separate from the building permit and easy to miss: both pre-approved plan submittal checklists require a Fire Flow Letter from Cal Water, dated within the past year, confirming 500 gallons per minute at 20 psi residual pressure from a hydrant within 600 feet of the ADU’s farthest corner. That’s a document you get from the water utility before you submit, not something the Building Division checks for you after the fact. Beyond that, the city’s own ADU FAQ points to state law (Government Code sections 65852.2(f) and 66000) for how utility connection fees get handled: an ADU generally isn’t treated as a new residential use for water and sewer connection fee purposes, and any charge has to be proportionate to the ADU’s actual burden on the system, not billed like a whole new house. Sewer specifically: the city allocates one lateral per parcel, and an ADU typically shares it rather than getting its own connection, though your bill goes up with the added volume.

fee	amount	notes
ADU Building Permit	$0.00	Waived per FY2025-2026 fee schedule, effective July 1, 2025
ADU Plan Check	$0.00	Waived, same fee schedule
ADU Electrical, Mechanical, or Plumbing Permit	$0.00	Waived, same fee schedule
Construction Tax (LAMC Chapter 3.24)	$0.42 per sq ft of residential construction	Not waived; no matching $0.00 ADU line in the schedule
Outside agency fees (Cal Water fire flow letter, sanitary district, PG&E)	Varies by agency	Set by each utility, not the city’s own fee schedule

Source: City of Los Altos Development Services Fee Schedule for Fiscal Year 2025 to 2026

I want to be direct about what that table does and doesn’t mean. The $0.00 lines are real and they’re not size-limited the way the state’s under-750-square-foot impact fee exemption is, the fee schedule document doesn’t carry that qualifier on the ADU permit and plan check lines. What isn’t zero: the construction tax under Los Altos Municipal Code Chapter 3.24 still applies at $0.42 per square foot of residential construction, since I found no matching $0.00 ADU line item for it, and outside agency charges like the Cal Water fire flow letter and any sanitary district fees sit outside the city’s own schedule entirely. Confirm your specific project against the current schedule at submittal, since these get revised annually. For the fuller build budget, not just the permit line, our Los Altos ADU cost breakdown walks through the rest of what actually drives price here.

phase	duration	notes
Intake & completeness review	About 1 week (2 to 5 business days)	Verified from the city’s Building Division and Permit Submittal Process pages
Plan check, pre-approved plan (either tier)	2 to 4 weeks	Builder-experience estimate; only site-specific items need review
Plan check, custom design	4 to 8 weeks	Builder-experience estimate; must resolve within the statutory cap below
Corrections & recheck	1 to 3 weeks per round	Builder-experience estimate; not separately published by the city
Permit issuance	Under 1 week	Once approved and any applicable charges are paid

Source: Los Altos Municipal Code Chapter 14.14 (60-day statutory cap); phase-by-phase durations are not separately published by the city and reflect typical builder experience

Here’s what I can and can’t verify on timeline. Los Altos Municipal Code Chapter 14.14 requires a complete ADU application to be approved or denied ministerially, with no discretionary review and no public hearing, within 60 days, and that clock tolls if the applicant asks in writing for a delay. That’s the hard ceiling, roughly 8 to 9 weeks. What the city doesn’t publish is a phase-by-phase breakdown inside that window. The intake figure above is genuinely verified from two of the city’s own process pages. The plan check and corrections rows are my honest estimate based on how these reviews typically run, not a number Los Altos states anywhere, and I’d rather tell you that plainly than dress up a guess as an official figure.

Why Los Altos Waives Its Own ADU Permit Fees

I don’t have a stated reason from the city for why it zeroed these out, and I’m not going to invent a policy rationale it hasn’t published. What I can do is put a number on what it actually saves you. A comparable ADU permit package in a nearby city commonly runs several thousand dollars once plan check and building permit issuance are added together, and in bigger cities like Los Angeles that combined figure often lands in the $5,000 to $15,000 range. In Los Altos, the equivalent building permit, plan check, and MEP permit lines are $0.00, full stop.

What that doesn’t cover: the construction tax under LAMC Chapter 3.24 still applies at $0.42 per square foot, and it has no matching ADU exemption line in the fee schedule, so I’m treating it as owed rather than assuming it’s swept into the same waiver. Outside-agency charges, the Cal Water fire flow letter process, any sanitary district charges, aren’t part of the city’s own schedule either. And I want to say this as plainly as I can: this is a real, city-published fact, sitting in the city’s own FY2025-2026 fee document, not a typo, not a misread line item, and not something I’m inferring from a secondary source. If you want to see it in the same table where I found it, our Los Altos ADU cost breakdown walks through the full fee schedule alongside construction costs.

The Los Altos Two-Tier Pre-Approved Plan System

This is the other lever most homeowners here don’t fully use, and it’s a genuine two-tier system, not one program with options.

Tier one: the city’s own permit-ready plans. Los Altos designed and owns a set of detached ADU plans in three sizes, roughly 525, 854, and 1,190 square feet, and three architectural styles: Mediterranean, Traditional, and Contemporary. They’re free, and they come with full structural calculations, mechanical, electrical, and plumbing plans, and energy code reports already done. The city’s own submittal requirements state plainly that modifications to these plans aren’t allowed, beyond a limited set of built-in customization options. You’re not paying for a fresh design, and you’re not getting to redesign it either.

Tier two: privately-designed pre-approved plans. Separate from the city’s own set, Los Altos also posts pre-approved detached ADU plans that private designers submitted and got cleared. As of this research, that roster includes Wellmade’s Fillmore model at 330 square feet (permit PAADU26-00001) and Ashbury model at 434 square feet (permit PAADU25-00010), plus ADORE Homes’ HUD model at 800 square feet (permit PAADU25-00005). To use one, you contact the designer directly, purchase the plan set, and then submit it to the city with your site-specific documents, survey, site plan, CalGreen checklist, and the Cal Water fire flow letter among them, layered on top of the already-approved architectural set.

Both tiers share the same disqualifiers, and this is where I’d actually pay attention if I were you. A property isn’t eligible for either pre-approved track if it sits in a flood zone other than Zone X or D (you’d need a standard permit demonstrating compliance with LAMC Chapter 12.60 instead), or if it’s listed on the Historic Resource Inventory, which requires a Historic Permit from the Planning Division under LAMC Chapter 12.44 before you can even apply for the building permit. Properties within 50 feet of a creek, involving protected tree removal, or needing a sewer sump and ejector pump due to insufficient sewer slope all trigger additional review or a deferred submittal on either track. Fire access matters too: structures more than 200 feet from an access road or 600 feet from a hydrant, or sites that can’t demonstrate the required fire flow, get kicked to additional Fire Department review regardless of which plan tier you’re using.

Los Altos-Specific Rules That Trip People Up

Large lots don’t buy you a bigger ADU

Much of Los Altos sits in R1-10, R1-20, or R1-40 zoning under LAMC Chapter 14.06, with minimum lot sizes running from 10,000 up to 40,000 square feet. That’s genuinely large-lot territory for California. But the state’s 1,200-square-foot cap on detached ADUs doesn’t scale with lot size, so a 40,000-square-foot parcel doesn’t get you a bigger unit than a 10,000-square-foot one does. What the extra land buys is siting flexibility, more room to hit setbacks and building separation without fighting the lot.

The JADU owner-occupancy question is genuinely open right now

AB 1154 narrowed the state rule so owner-occupancy only applies when a JADU shares a bathroom with the main house. As of this research, the city’s own published ADU guidance still reads like a blanket owner-occupancy requirement for JADUs, without that narrower carve-out written in. Honestly, I’m not sure whether that’s outdated language the city hasn’t gotten to yet or a position they still intend to hold, and given the active HCD letter sitting on this city’s ordinance right now, I wouldn’t guess either way. Ask the Building Division directly which version applies to your JADU before you plan around either answer.

A Historic Resource Inventory listing knocks out your fast lane

If your property is on that inventory, neither pre-approved plan tier is available to you. You’d need a Historic Permit from the Planning Division under LAMC Chapter 12.44 before the building permit application even starts, which is a genuinely different, slower track than the ministerial ADU review everyone else gets.

No partial or phased inspections

Because Los Altos runs as a combination jurisdiction, all your rough inspections, framing, electrical, plumbing, mechanical, happen together at one visit. That’s worth knowing before you assume you can schedule electrical rough-in separately from framing just because your contractor finished that piece first.

An abandoned application really does die at 180 days

If a submittal sits without activity for 180 days and isn’t being pursued in good faith, the city considers it abandoned. That’s not a soft deadline; keep the file moving.

What I’d Do If I Were Permitting in Los Altos Right Now

I’d check both pre-approved plan tiers before commissioning anything custom, starting with the city’s free permit-ready plans since they already include full structural and MEP drawings at no design cost. If none of the three sizes or styles fit the site, I’d look at the private roster next, Wellmade’s smaller units and ADORE Homes’ 800-square-foot model cover a decent range before you’re paying for a from-scratch design.

I’d also call Cal Water early for the fire flow letter rather than waiting until plan check flags it, since it has to be dated within the past year and it’s one of the few pieces of this process that doesn’t run through the Building Division at all. And if your JADU plan hinges on the owner-occupancy question, I’d get that answer from the city in writing before I designed around either version of the rule.

Frequently Asked Questions

Does Los Altos really charge $0 for ADU permits?

Yes, for three specific line items. The city’s own FY2025-2026 Development Services fee schedule lists the ADU building permit, ADU plan check, and ADU electrical, mechanical, or plumbing permit at $0.00 each, effective July 1, 2025. The construction tax under LAMC Chapter 3.24 and any outside utility agency fees still apply.

How long does an ADU permit take in Los Altos?

Realistically 3 to 9 weeks depending on whether you use a pre-approved plan or a custom design. The hard statutory ceiling is 60 days, about 8 to 9 weeks, under Los Altos Municipal Code Chapter 14.14, which requires ministerial approval with no discretionary review.

What department handles ADU permits in Los Altos?

The Building Division, reached at bldpermit@losaltosca.gov for plan check submittals. The Planning Division gets involved for specific triggers like Historic Permits, tree removal permits, and creek-proximity review.

Are there pre-approved ADU plans available in Los Altos?

Yes, in two separate tiers. The city offers its own free permit-ready plans in three sizes and three styles with full structural and MEP drawings included, and modifications to those aren’t allowed. Separately, a roster of privately-designed pre-approved plans, including options from Wellmade and ADORE Homes, are available for purchase directly from those designers.

Does a large lot let me build a bigger ADU in Los Altos?

No. Detached ADUs are capped at 1,200 square feet under state law regardless of lot size, so R1-20 and R1-40 zoning with their 20,000 and 40,000 square foot minimums don’t translate into extra square footage. They mostly buy siting flexibility on setbacks and building separation.

If you’re comparing Los Altos against a bigger neighboring market, our San Jose ADU permit guide covers a very different fee structure just a few miles away, and our California permit overview covers what applies statewide before you get into any city’s specific rules. The permits pillar and Data Hub are the right next stops if you’re planning across multiple cities, and for the full construction budget rather than just the permit line, go back to our Los Altos ADU cost breakdown.