Building an ADU in Sierra Madre. Rules, costs, timeline.

Can I build an ADU in Sierra Madre?

Five things to know before you start

If you read nothing else on this page, read these. They are the five points that change the most Sierra Madre projects.

How many accessory units one lot can hold

Everything in this section is grounded in Sierra Madre Municipal Code Chapter 17.22, as amended by Ordinance No. 1494 (adopted May 26, 2026), with state-law citations called out where they preempt or supplement the local rule. We will not re-cite the local chapter on every line; assume it under each subsection unless we say otherwise.

Most homeowners assume the answer is one. It is not. Gov. Code § 66323(a)(1)–(2) and the HCD ADU Handbook (March 2026, p. 17) require every California city to allow three things to be combined on a single-family lot:

Sierra Madre’s subsection 17.22.060(A) tracks that structure, and expressly says the detached 800-square-foot unit “may be combined with a junior accessory dwelling unit” from the paragraph above it. Where the local text reads more narrowly than the state stack on any of the three, state law controls (Gov. Code § 66316).

Owner-occupancy

You do not have to live on the property to build or rent an ADU. Gov. Code § 66315 bars the City from requiring it, and the ordinance does not attempt to. A junior ADU is the one exception, and Sierra Madre has already written the current version of that rule into its code: subsection 17.22.050(A) requires the owner to live in either the house or the junior ADU only where the junior ADU shares sanitation facilities with the primary structure. That matches AB 1154, effective January 1, 2026, which amended Gov. Code § 66333 to narrow the requirement to shared-bathroom cases. Give the junior ADU its own bathroom and the requirement does not reach you.

This is worth noticing. Most LA-area ordinances still carry the broader pre-2026 language and rely on state law to correct it. Sierra Madre fixed the text.

What an ADU costs in Sierra Madre (2026)

Our Signature plans are fixed-price — architectural design and full permit processing included, the same number whether the lot is in Sierra Madre, Pasadena or the Valley. Construction is separate: once your plans are permitted, you build it yourself, bring your own licensed contractor, or build with one of our vetted construction partners. The figures below are the estimated cost to build each single-storey model with an independent licensed general contractor.

The 750-square-foot fee line, in dollars

This is the newest and most consequential number on the page, and it did not exist three months ago. Under City Council Resolution 26-50, Public Facilities Fees apply to ADU permit applications received on or after July 1, 2026. The City’s notice is explicit that ADUs with 750 square feet or less of interior livable space are exempt, which matches the state exemption in Gov. Code § 66311.5(c)(1) and the ordinance’s own subsection 17.22.120(C).

Above 750 square feet the arithmetic runs in three steps. Start from the FY 2026–2027 base — $76,393.44 for a single-family rate, across seven categories, of which parks ($20,050.98), sewer ($21,079.23) and water ($18,358.37) are the largest. Reduce it proportionally to the ADU’s size against the primary dwelling. Then apply the Resolution 26-50 multiplier, which depends on how many ADUs already exist, are in construction, or are approved on the property.

The example runs the base through a 50 percent size ratio and then the multiplier. The multifamily rate ($37,296.47) applies instead where the ADU sits in a zoning district that allows multifamily development. Fees accrue when the application is submitted and are calculated at the rate in effect that day, so the application date matters. Payment can be deferred to final inspection, but the full balance is due before a Certificate of Occupancy issues.

The other Sierra Madre line items

Building-permit and plan-check fees are valuation-based and set by City Council resolution, so they scale with the project rather than sitting at a flat number. Beyond those, three costs are specific to this city and each is paid by the applicant:

• Historic resource evaluation report. Required under SMMC § 17.22.140 where the project alters or demolishes a preservation candidate, prepared on California Department of Parks and Recreation Series 523 forms. If the result is a status code of 1 through 5, a Historic Resource Design Review by a qualified historian follows.
• Arborist report. Required under SMMC § 17.22.150 where a protected oak, sycamore or black walnut is affected. The arborist is selected by the City and paid for by you, and a tree removal or trimming permit carries its own fees.
• Utility connection. The ADU connects to the house’s existing water and sewer service, and the City may not charge a connection fee or capacity charge unless the ADU is built together with a new house. Separate water meters are not permitted unless the Director of Utilities Services finds a shared connection infeasible.

What it returns: renting your ADU

Sierra Madre sits inside the Los Angeles–Long Beach–Glendale HUD Metro Fair Market Rent Area. For fiscal year 2026, HUD publishes Fair Market Rents of $1,863 for a studio, $2,085 for one bedroom, $2,601 for two bedrooms and $3,298 for three. Those are the government benchmark for the whole metro, and a new detached ADU in a foothill town with this school district and this walkability typically rents at or above them — new construction, its own entrance, no shared walls.

One constraint shapes every rent projection here: the term. The ordinance permits rentals of no less than 30 days and prohibits using or advertising an ADU as a short-term rental, and it requires the owner to hold an annual business license while renting. There is no nightly-rate path in Sierra Madre. Run the numbers on a 30-plus-day tenancy or the project will not work the way you expect.

When an ADU isn’t the right move

Not every Sierra Madre property is a good ADU candidate, and it is cheaper to learn that now than after you have paid for plans. Four situations where we would tell you to wait, change the unit type, or not build:

• Your numbers depend on nightly rental income. They will not work. Section 17.22.130 sets a 30-day floor and bans short-term-rental advertising outright, with no ADU carve-out. If the pro forma needs a nightly rate, the project does not pencil here.
• You want to sell the unit separately one day. Sierra Madre has not opted into AB 1033, and subsection 17.22.080 prohibits separate ownership or sale. An ADU here is an income and family-housing asset, not a separable one.
• You are planning to expand the main house later. Section 17.22.015 spells out the trap: an 800-sqft ADU can push your total floor area past what the zone allows, leaving the property legally nonconforming and blocking future additions. Do the addition first, then add the ADU. The City makes this point in its own guidance and it is good advice.
• Your project needs a hard, short deadline and your house is old or your yard is wooded. The 60-day ministerial clock is real, but it starts on a complete application — and a historic resource evaluation or a City-selected arborist report has to be in hand before the application is complete. Those run on their own schedules. Neither we nor any builder can compress them.

The rules that make Sierra Madre different

Historic resource evaluation

Sierra Madre was laid out in the 1880s and much of its housing stock is old enough to matter. Under subsection 17.22.140, if your ADU project alters or demolishes a structure that is a “preservation candidate” as defined in SMMC § 17.60.056, you must prepare a written historic resource evaluation report. The City’s published ADU guidance describes the trigger in plainer terms: a property with a year-built date more than 75 years before the date the building permit application is received. You can check your year built on the Los Angeles County Assessor portal.

The report goes on California Department of Parks and Recreation Series 523 forms and returns a status code:

• Code 6 — not eligible for designation. You proceed under the ordinance with no further historic review.
• Codes 1 through 5 — eligible. A Historic Resource Design Review follows, prepared by a historian qualified under the Secretary of the Interior’s Professional Qualification Standards and selected by the City. Its mitigation measures become conditions of approval and must appear on your building plans.
• Code 7 — insufficient information. The property is re-evaluated against the missing criteria and the application is deemed incomplete until a code of 1 through 6 comes back.

Two things soften this. Creating an ADU is expressly not subject to the discretionary demolition permit that § 17.60.056 would otherwise require — the ordinance says so directly, to keep ADU permitting ministerial. And on a property already designated a historic landmark, the evaluation step is skipped and you go straight to design review.

Protected trees

Oak, sycamore and black walnut are protected under SMMC § 12.20.020. Where the Director of Public Works determines that your ADU requires removal or substantial trimming of one, subsection 17.22.150 requires a tree survey and arborist report prepared by a certified arborist selected by the City and paid for by you, under SMMC § 12.20.115. The report documents trunk and drip-line locations, species and diameter at breast height, condition, project impact, ISA valuation, and recommended mitigation and monitoring. Public Works reviews it alongside your ADU application and may impose its recommendations as conditions of approval. A separate removal or trimming permit and its fees come before any work.

The practical takeaway is a siting one. The City describes the trigger as construction under a protected canopy, so a unit placed clear of drip lines avoids the whole sequence. On a foothill lot that may not be possible — in which case order the report early and treat it as a design input rather than a hurdle.

Fire — the Very High Fire Hazard Severity Zone

Sierra Madre lies within a state-designated Very High Fire Hazard Severity Zone. That does not restrict ADUs, and it is worth being precise about what it does and does not require. Under subsection 17.22.030(B), building an ADU or junior ADU cannot trigger a sprinkler requirement in your existing house, and sprinklers are not required in the ADU itself except where a sprinkler system has been or is required to be installed in the primary residence, or where the fire department deems it necessary. The first two match Gov. Code § 66314(d)(12).

What does apply to every new ADU: fire-resistant building materials, compliance with SMMC Chapter 15.24, compliance with Chapter 8.36 on hazardous brush clearance, and — where two ADUs share a common wall — a one-hour fire wall between them. The City also notes that the Fire Marshal may find access to a proposed ADU insufficient for emergency services, which is an access-and-siting question worth raising before you finalise the position of the unit.

Design matching, roof decks and the covenant

Three smaller rules catch people out. An attached new-construction ADU must match the existing house on building form, colour tones, window design, door and window trims, roofing materials and roof pitch, except where a different treatment is needed to preserve historic architectural value. No new roof decks are permitted on any ADU or junior ADU. And before a building permit issues you must record a covenant or deed restriction running with the land, committing the unit to comply with Chapter 17.22 and state law.

Selling separately — and other recent state-law changes

You cannot sell a Sierra Madre ADU separately from the house. Subsection 17.22.080 prohibits separate ownership or sale, and the City has not adopted an AB 1033 condominium opt-in, which is what Gov. Code §§ 66340–66342 would require. Of the LA-area cities we track, only a handful have opted in. Note one wrinkle: Ordinance 1494 removed the ordinance’s former cross-reference to the separate-conveyance exception now codified at Gov. Code § 66342, which covers units built by a qualified nonprofit. That state-law path is not mentioned in the current local text. If it applies to your situation, raise it with Planning directly.

Three other recent changes are already reflected in the local code, which is genuinely unusual and worth crediting. SB 1211 (effective January 1, 2025) raised the detached count on existing multifamily lots to eight, and Ordinance 1494 wrote eight into subsection 17.22.060(A)(4). AB 1154 (effective January 1, 2026) narrowed junior-ADU owner-occupancy to shared-sanitation cases, and subsection 17.22.050(A) now says exactly that. SB 543 (effective January 1, 2026) added the 15-business-day completeness clock, and subsection 17.22.100(B) carries it including the deemed-complete consequence. Sierra Madre’s ordinance is more current than most in the county.

One place the local text still lags: subsection 17.22.130(A) permits rentals of “no less than thirty days,” while Gov. Code § 66323(e) requires a term longer than 30 days for a state-mandated unit — which the ordinance’s own subsection 17.22.060(D) states correctly. For a unit built on the § 66323 track, use the longer reading.

Official sources

Where the local code and state law differ, the more permissive of the two controls: state law sets a floor a city cannot drop below. On most points Sierra Madre now meets that floor exactly, which is the practical reason this page cites state law as often as it cites the ordinance.

Last verified against primary sources on August 17, 2026, against Ordinance No. 1494 Exhibit 1, the City’s ADU page, and the July 1, 2026 Public Facilities Fee notice. State ADU law changes every January 1 and Sierra Madre amended its own chapter twice in four years. If you are reading this six months from now, confirm the current version before you commit to a design — or call us and we will confirm it for you.