Building an ADU in Monrovia. Rules, costs, timeline.
What Monrovia Municipal Code § 17.44.005 actually allows after the City's 2025 rewrite, how the historic-landmark and Mills Act standards shape a backyard build, and what an all-in project costs on a Monrovia lot in 2026.
What you can build — at a glance
Reviewed by CALI ADU’s ADU specialists · August 2026
- Max ADU size
- 800–1,000 sqft Streamlined track: a converted ADU with no maximum, plus a new detached ADU up to 800 sqft. Alternative track: one larger ADU, up to 1,000 sqft detached. Minimum 150 sqft. JADU: 500 sqft.
- Detached height
- 16 ft 18 ft within ½ mile walking distance of a major transit stop or high-quality transit corridor, plus 2 ft to match the primary roof pitch — written into the ordinance itself since the 2025 amendment.
- Attached height
- 25 ft · 2 stories Or the zoning district’s height limit, whichever is lower — but that clause may not push an attached ADU below the 25-ft state floor.
- Side & rear setbacks
- 4 ft The state floor. No setback at all for a conversion of an existing structure, or for a rebuild in the same location and dimensions. Conversions need only what fire and safety require.
- Units per SFR lot
- Up to 2 ADUs + 1 JADU A converted ADU and a new detached ADU up to 800 sqft, granted expressly “pursuant to both,” plus one JADU. The full state stack, written into the local code.
- Parking required
- 1 space · usually waived Ten enumerated exemptions, including every streamlined-track ADU, any new 800-sqft unit with 4-ft setbacks, a historic district, and ½-mile transit proximity. A JADU never needs one.
- Permit timeline
- 60 days Ministerial building-permit review by the Director — no hearing, no discretionary design review, no neighbor sign-off.
- Historic homes
- Design standards, not a veto On a landmark or a historic-district contributor, an ADU may not change the street-facing facade and must match existing features. A streamlined-track ADU is exempt from the Certificate of Appropriateness section entirely.
- Detached Up to 800 sqft on the streamlined track, 1,000 sqft on the alternative track · 16 ft
- Attached The lesser of 50% of the house or 1,000 sqft, never below the 850/1,000 sqft state floor · up to 25 ft
- Garage conversion Full existing footprint, no maximum · up to 150 sqft added for ingress and egress · no replacement parking
- Interior conversion Carved from existing or proposed space in the house · setbacks only as fire and safety require
- Junior ADU Up to 500 sqft inside the single-family home — an attached garage counts as part of the house
Per Monrovia Municipal Code § 17.44.005 (Accessory Dwelling Units and Junior Accessory Dwelling Units, Ord. 2020-10 § 12, 2020, as amended by Ord. 2025-01 § 8, 2025) and Gov. Code §§ 66310–66342. Cross-checked against the HCD ADU Handbook (March 2026). Full citations in the sections below.
On this page
Can I build an ADU in Monrovia?
Five things to know before you start
If you read nothing else here, read these. They are the five points that change the most projects in this city.
| What to know | Why it matters for your project |
|---|---|
| 1. The chapter was rewritten in 2025 | Ordinance 2025-01 amended MMC § 17.44.005 and restructured it end to end. Height tiers, unit counts, minimum size, parking exemptions and subsection letters all changed. Anything you read about Monrovia ADUs written against the 2020 text — including an older version of this page — describes rules that no longer apply. |
| 2. There are two tracks, and picking one is the real decision | The streamlined track at subsection (D) delivers the state-law units: a conversion, a JADU, and a new detached unit up to 800 sqft. The alternative track at subsection (E) delivers one larger unit, up to 1,000 sqft, and takes the design standards with it. Choose before you draw. |
| 3. Detached means single story | A new detached ADU is capped at 16 feet, or 18 feet plus 2 feet of roof pitch near major transit. That is the state floor written into local code, not a Monrovia quirk — and it settles the product question before it comes up. |
| 4. A historic designation changes the design, not the answer | On a landmark or a historic-district contributor the ordinance sets objective design standards; it does not create a veto, and it does not make review discretionary. A streamlined-track ADU skips the Certificate of Appropriateness section altogether. |
| 5. Long-term rental only | Short-term rental of an ADU is prohibited and every rental must run 30 consecutive days or more. State law requires that floor rather than merely permitting it (Gov. Code §§ 66323(e), 66333(g)). If nightly income is the plan, the numbers will not work here. |
How many units your lot can take
Everything in this section is grounded in MMC § 17.44.005 as amended by Ordinance 2025-01, and in Gov. Code § 66323; we won’t re-cite the local section on every line. The short version is that Monrovia now writes the state unit stack into its own code rather than leaving homeowners to argue for it.
Subsection (D)(1) says a single-family lot may develop ADUs “pursuant to both” of its two paragraphs: one converted ADU inside the existing or proposed house or an existing accessory structure, and one new detached ADU of up to 800 sqft. Subsection (D)(3) then adds one JADU of up to 500 sqft inside the house. That is two ADUs plus a junior ADU — exactly the combination Gov. Code § 66323(a)(1)–(2) requires, and the combination the HCD ADU Handbook (March 2026), p. 17, works through as its example.
On a lot with an existing multifamily building, subsection (D)(2) allows conversion of non-livable space — storage rooms, boiler rooms, attics, basements, garages — into at least one ADU and up to 25% of the existing unit count (Gov. Code § 66323(a)(3)(B)), plus up to eight detached ADUs, capped at the number of existing units (Gov. Code § 66323(a)(4)(A)(ii)). A lot proposed for a new multifamily building gets two. JADUs remain a single-family product.
Owner-occupancy
You do not have to live on the property to build or rent an ADU in Monrovia. The chapter imposes no owner-occupancy requirement on an ADU, and Gov. Code § 66315 forbids a city from imposing one. An investment build and a family-flex build are treated the same way.
What can you build?
The numbers below come from MMC § 17.44.005, with state-law citations called out where the statute preempts or supplements the local rule. Assume that anchor under each subsection unless we say otherwise. The section runs on two parallel tracks: (D) is the streamlined ministerial track for the units state law guarantees, and (E) is the alternative-local-standards track for one larger unit.
Which ADU type fits your property?
Monrovia permits five types. On these lots the right one is usually decided by two things: how much of the yard you want back, and whether the house carries a historic designation.
| If this sounds like you | Start with | What that means |
|---|---|---|
| You have a deep rear yard and want the most space, privacy and rental value | Detached ADU, alternative track | Up to 1,000 sqft, single story at 16 ft, 4-ft side and rear setbacks. Takes the objective design standards at subsection (E)(6) with it — matching siding, roof pitch, window proportions. |
| Your house is a landmark or a historic-district contributor, or the lot is tight | The 800 sqft streamlined unit | A new detached ADU of up to 800 sqft at 16 ft with 4-ft setbacks under subsection (D)(1)(b). It is exempt from § 17.40.090 and from the parking requirement, and Gov. Code § 66321(b)(3) protects it against floor-area and lot-coverage math. |
| You have a detached garage or workshop you rarely use | Garage or accessory conversion | Use the structure’s full existing footprint with no maximum size, plus up to 150 sqft for ingress and egress. Setbacks only as fire and safety require, and no replacement parking for the stalls you lose. |
| You want the unit under the existing roof and the yard to stay open | Interior conversion | Carve the ADU from existing or proposed space in the house. No maximum size, separate exterior access required, and it stacks with a new detached unit on the same lot. |
| You are housing a family member and want the lowest-cost path | Junior ADU (JADU) | 150 to 500 sqft inside the single-family home, with a kitchen or efficiency kitchen. An attached garage counts as part of the house. No parking may ever be required. |
Maximum size
| Standard | Limit |
|---|---|
| Converted ADU, streamlined track | No maximum — the existing footprint, plus up to 150 sqft for ingress and egress on an accessory-structure conversion |
| New detached ADU, streamlined track | 800 sqft, protected regardless of floor-area or lot-coverage limits (Gov. Code § 66321(b)(3)) |
| New detached ADU, alternative track | 1,000 sqft |
| New attached ADU, alternative track | The lesser of 50% of the single-family dwelling or 1,000 sqft — lifted to 800 sqft by the ordinance’s own savings clause, and never below 850/1,000 sqft under Gov. Code § 66321(b)(2) |
| Minimum unit size | 150 sqft, or whatever an efficiency unit requires. The 2025 amendment dropped this from 220 sqft |
| JADU | 150 to 500 sqft, inside the single-family home (Gov. Code § 66313(d)) |
The percentage rule on attached ADUs is the one people get wrong. On a 1,400 sqft house, 50% computes to 700 — but the ordinance itself lifts the cap to 800 sqft where the percentage would block an 800-sqft unit with 4-foot setbacks, and Gov. Code § 66321(b)(2) puts a harder bottom under it still: no city may cap an ADU below 850 sqft for a studio or one-bedroom, or below 1,000 sqft with two or more bedrooms. The percentage never wins against those floors.
Maximum height
| ADU type | Height limit |
|---|---|
| New detached ADU | 16 ft — the state floor (Gov. Code § 66321(b)(4)(A)) |
| Detached, within ½ mile walking distance of a major transit stop or high-quality transit corridor | 18 ft, plus 2 ft to carry a roof pitch matching the main house (Gov. Code § 66321(b)(4)(B)) |
| Detached, on a lot with a multistory multifamily structure | 18 ft (Gov. Code § 66321(b)(4)(C)) |
| New attached ADU | 25 ft and two stories, or the zoning district’s limit, whichever is lower — but never below the 25-ft state floor (Gov. Code § 66321(b)(4)(D)) |
Monrovia has a Metro A Line rail station, and the ordinance’s own definition of a major transit stop covers a rail station, so parcels within a half-mile walking distance of it pick up both the 18-foot detached tier and the parking exemption. Walking distance is a measured test, not an eyeball one — confirm your parcel before you draw to 18 feet. For most Monrovia lots, spreading out across a deep rear yard is cheaper than reaching for the extra two feet anyway.
Setbacks and placement
Side and rear setbacks are 4 feet for a new attached or detached ADU, and for any addition beyond an existing footprint. That is exactly the state floor in Gov. Code § 66314(d)(7), and a city may not require more of a conforming ADU. Converting an existing living area or accessory structure needs no setback at all. Neither does a structure rebuilt in the same spot and to the same dimensions as one that was demolished, except as fire and safety require.
Two placement details are worth knowing early. Decks a foot or more above grade and balconies keep the primary dwelling’s setback, and an upper-floor deck may not face an interior property line. Ground-mounted air conditioning equipment sits at least 4 feet off a side property line, or 3 feet in the rear yard, and roof-mounted equipment is out unless a parapet hides it completely.
Parking
| Requirement | Monrovia rule |
|---|---|
| Standard ADU | One on-site space, on top of what the primary dwelling already needs |
| Exemptions that zero out the space | Ten of them, including a JADU · any streamlined-track ADU · any new 800-sqft unit with 4-ft setbacks · ½-mile walking distance of public transit · a historically significant historic district · part of the primary residence or an accessory structure · an on-street-permit area · car-share within a block (Gov. Code § 66322) |
| Garage, carport or covered space converted or demolished for the ADU | No replacement parking may be required (Gov. Code § 66314(d)(11)) |
| JADU | None, ever — a city may not require parking for a JADU (Gov. Code § 66334(a)) |
| Where a space is required | Covered, uncovered or tandem, and allowed in the front, side and rear setback areas — but in the front yard only on the driveway, and no more than 25% of the front yard |
Design standards and utilities
The alternative track carries a real design package. A new attached or detached ADU has to match the primary dwelling’s architectural features where the house has them: exterior siding materials, roof pitch and eave type, window proportions and shapes, window grilles, and cornices and bay windows. That is a genuine constraint on a Craftsman or a Victorian, and it is also why our traditional-gable plans get picked here. The whole package yields where it would block an 800-sqft detached unit with 4-foot setbacks at the permitted height — the ordinance says so in its own text.
Utilities follow the unit type. An ADU is not treated as a new residential use for connection fees or capacity charges unless it is built alongside a new single-family dwelling. A JADU, or an ADU inside the existing residence, cannot be required to take a new or separate meter and cannot be charged a related connection or capacity fee. A detached ADU is the exception: it may be required to take its own meter, with a connection fee or capacity charge proportionate to the unit’s size or fixture count. If the lot runs on an on-site wastewater system, the City wants a percolation test certified within the last five years, or recertified within the last ten.
Signature Homes that fit the 16-foot envelope
Single-story plans engineered to sit under the detached height cap — gable profiles that belong behind a Craftsman on a Monrovia street. Fixed plan fees, transparent build estimates.
The Laurel Canyon
The Melrose
The Lincoln
Our two-story plans stand roughly 25 feet, so they cannot be permitted in Monrovia as drawn as detached units — the detached envelope is 16 ft, or 18 ft within ½ mile walking distance of a major transit stop, plus 2 ft to carry the primary roof pitch (MMC § 17.44.005(D)(1)(b)3., (E)(4)(b)). Monrovia does allow 25 ft and two stories for an attached ADU (MMC § 17.44.005(E)(4)(a); Gov. Code § 66321(b)(4)(D)), so the height itself is not the barrier — our two-story plans are drawn as detached buildings. That is a constraint on the stock plan, not on the project: a two-story plan can be modified to fit the lower detached envelope, or we design a custom ADU from scratch ($9,990–$19,990 for design and permit processing, bid per project). The single-story plans permit as drawn, which is why they lead.
What an ADU costs in Monrovia (2026)
Our Signature plans are fixed-price. Architectural design and full permit processing are included, and it is the same number whether the lot is in Old Town, north of Foothill, or over in Arcadia. 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 model with an independent licensed general contractor.
| Model | Configuration | Size | Collection | Est. cost to build |
|---|---|---|---|---|
| The Wilshire | Studio / 1BA | 400 sqft | Single-story | $180K–$200K |
| The Sunset | 1BR/1BA | 480 sqft | Single-story | $200K–$215K |
| The Westwood | 1BR/1BA | 550 sqft | Single-story | $215K–$235K |
| The Laurel Canyon | 2BR/1BA | 660 sqft | Single-story | $240K–$265K |
| The Melrose | 2BR/2BA | 800 sqft | Single-story | $275K–$295K |
| The Lincoln | 3BR/2BA | 1,000 sqft | Single-story | $325K–$350K |
| The Fairfax | 2BR/1.5BA | 840 sqft | Two-story | $280K–$310K |
| The Venice | 2BR/2.5BA | 1,080 sqft | Two-story | $335K–$365K |
| The Culver | 3BR/2.5BA | 1,200 sqft | Two-story | $385K–$420K |
The two-story models are shown for reference. In Monrovia the detached envelope is single story, so the Lincoln at 1,000 sqft is the ceiling as drawn — and it lands exactly on the alternative track’s detached size cap. Custom work is priced per project, $9,990–$19,990 for design and permit processing.
City fees and pass-throughs
A conforming ADU in Monrovia is a ministerial building permit, so there is no planning entitlement to buy. What you pay is the City’s valuation-based building-permit and plan-check fees, plus any utility connection charge where a detached unit takes its own meter. We do not publish a dollar figure for those here. The City’s schedule is adopted by resolution and revised periodically, and a stale number is worse than no number. Confirm the current figures with the Planning Division. Your Backyard Review includes a line-item estimate for your lot.
Two things are settled and worth banking. No development impact fee may be charged on an ADU of 750 sqft or less (Gov. Code § 66311.5(c)(1)), and above that threshold impact fees must be proportional to the primary dwelling’s size rather than charged flat per unit. Separately, subsection (H)(2) bars traffic impact fees on ADUs and JADUs under the City’s Chapter 3.22 unless that chapter is expressly amended.
What it returns: renting your ADU
Long-term rental only. For a rent benchmark, the government figure is HUD’s Fair Market Rent for the Los Angeles–Long Beach–Glendale HUD Metro FMR Area, which covers Monrovia. In the For FY 2026, as revised effective May 21, 2026: $2,079 for a studio, $2,328 for a one-bedroom, $2,903 for a two-bedroom, and $3,681 for a three-bedroom. Those are metro-wide figures spanning the full range of housing stock and unit ages, so treat them as a floor rather than a forecast. A newly built detached ADU near Old Town or the A Line station typically rents above FMR — we would rather point you at a verifiable number than an invented one. A local property manager can price your specific street.
HUD FMR figures: FY 2026 Schedule of Metropolitan & Non-Metropolitan Fair Market Rents, Los Angeles–Long Beach–Glendale, CA HMFA (huduser.gov), read August 24, 2026. Your ADU’s actual performance depends on finish level, lot, access, and the rental market at the time you lease it. For payback math keyed to your lot, use the ADU ROI calculator or the ADU calculator.
When an ADU isn’t the right move
Not every Monrovia 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, pick a different unit type, or not build:
- Your numbers depend on short-term rental income. They will not work. Subsection (G)(1) prohibits it outright and sets a 30-day floor that state law requires rather than merely permits. Run the math on a 30-day-plus tenancy or reconsider.
- You want a separate-sale exit. The City has not adopted an AB 1033 opt-in, so the ADU cannot be sold apart from the house. If a condominium-style exit is the plan, this is the wrong jurisdiction for it.
- You need two stories of detached space exactly as our stock plans draw it. The detached envelope is 16 feet, 18 near transit. The honest routes are a single-story plan, a modified two-story plan, or a custom design — not a variance, which takes the project out of ministerial review entirely.
- Your landmark house has no rear-yard pad and you want the larger unit. On a designated property, an alternative-track ADU carries both the matching-features standards and the historic standards. If the only buildable spot is visible from the street, the better move is a conversion inside an existing structure — or the streamlined 800-sqft unit tucked at the back.
How long an ADU takes
Here is what the schedule actually looks like on a Signature plan.
| Phase | Duration | Notes |
|---|---|---|
| Signature plan preparation | ~2 weeks | Pre-engineered plan customized to your lot — siting, the 4-ft envelope, transit-distance and historic-status checks, utility routing |
| City completeness check | 15 business days | The City determines completeness and notifies you in writing (SB 543, eff. Jan. 1, 2026; Gov. Code § 66317(a)(2)(A)) |
| Ministerial approval cycle | 60 days to a decision | MMC § 17.44.005(B)(3) directs the Director to act within the time limits in Gov. Code §§ 66317 and 66335; a complete application must be approved or denied within 60 days, and one that gets neither is deemed approved. Pre-engineered plans clear plan check in weeks, not months — it is a conformance review, not a from-scratch evaluation. |
| Construction | 4–6 months | By model size — the schedule is guaranteed in writing, with a daily delay penalty if the contracted finish date is missed |
| Total, start to finish | ~6–9 months | Signature plans only. Custom designs add bespoke design time and a longer plan check, because the City is reviewing the drawings for the first time. |
One more sequencing note. A demolition permit for a garage the ADU replaces is handled alongside the ADU permit, because the chapter puts associated demolition permits on the same ministerial timeline. That removes the most common ordering surprise on a garage-conversion project here.
The rules that make Monrovia different
Old Town, landmarks and the Mills Act
Monrovia has one of the San Gabriel Valley’s deepest stocks of historic homes. The Myrtle Avenue core in Old Town. The Craftsman and Victorian streets around it. A long list of designated landmarks and Mills Act contracts. If your house is one of them, subsection (E)(5) adds a layer of ADU rules on top of everything above.
Those rules are objective design standards, not a veto. They apply on a national, state or local landmark, and on a contributor within a designated historic district. No ADU may be approved that requires a change to the street-facing facade. Exterior changes must exactly match the existing architectural features. No ADU may be approved if it requires demolishing a landmark. And a property under a valid Mills Act contract follows the standards and conditions of that contract. Review stays ministerial throughout (Gov. Code § 66317).
A historic-district lot picks up a second benefit that has nothing to do with design: it is exempt from the ADU parking requirement outright (Gov. Code § 66322). Between that exemption and the streamlined track’s own exemption, a historic-lot ADU in Monrovia usually adds no parking at all.
The two tracks, and why the choice is strategic
Most city ADU ordinances have one set of standards. Monrovia has two, and they trade size against constraint. The streamlined track gives you the units state law guarantees — a conversion with no size cap, a new detached unit up to 800 sqft, and a JADU — and it exempts them from the parking requirement and from § 17.40.090. The alternative track gives you one larger unit, up to 1,000 sqft detached, and attaches the matching-features design standards, the historic standards, and the parking requirement unless another exemption applies.
There is one clause to plan around. Subsection (E)(7) says the minor exceptions available elsewhere in the code do not apply to ADUs, and that any deviation from the development standards in this section requires a variance from the Planning Commission. A variance is a discretionary process, so it is the one route that can take an ADU out of ministerial review.
The foothill edge and fire
Monrovia climbs into the San Gabriel foothills, and the state’s fire-hazard maps designate Very High Fire Hazard Severity Zone areas in the northern hillsides. The ADU chapter imposes no fire-zone ban — whether your parcel is mapped at all is a lookup on the state map, and it is the first thing we check on a hillside Backyard Review. What a mapped parcel changes is construction detailing and cost, not your right to build.
No separate-sale path
Subsection (G)(2) bars conveying an ADU separately from the lot and the primary dwelling except as Gov. Code §§ 66340 through 66342 provide, which preserves the narrow path for a unit built with a qualified nonprofit and nothing more. The condominium route needs a local AB 1033 opt-in ordinance (Gov. Code § 66342), and Monrovia has not adopted one. Among Los Angeles-area cities only a handful have — Santa Monica (SMMC § 9.31.026, 2025) and Culver City (CCMC § 17.400.096, 2026) among them. Build here for rental income, family housing or long-term value.
How the permit process works
Because a conforming ADU is ministerial, there is no entitlement to win first. The path is a building permit and its trade permits, reviewed against MMC § 17.44.005, with any associated demolition permit running on the same clock. If the plans comply, the application is approved — the Director has no discretion to deny a conforming project.
Which of the two tracks you file under matters more here than in most cities. Filing under the streamlined track at subsection (D) escapes the local design standards, the Certificate of Appropriateness section, and the parking requirement, at the price of an 800-sqft detached cap. Filing under the alternative track at subsection (E) buys 1,000 sqft and takes all three. Picking the track before you draw is worth more than any expediting trick.
The pre-approved plan program
Monrovia runs a Pre-Approved ADU Plan Program for homeowners, published on the City’s Community Development pages. It is the local answer to the statewide pre-approval mandate of AB 1332 (Gov. Code § 65852.27), which required every city to have a program running by January 1, 2025. A pre-approved plan is the fastest route across the counter, and it is built exactly as filed.
CALI ADU does not participate in the program. Our Signature plans are individually permitted on your lot and adapted to what these parcels actually present: rear-yard depth, grade at the foothill edge, historic status, and whether the unit is taking its own meter. If you want a standard plan built as-is on a simple lot, the City program is a real option worth looking at first. If you want a design and project-management partner with a fixed, transparent plan fee, that is us.
Monrovia ADU questions, answered
The questions homeowners here actually ask before they start — with citations to Monrovia Municipal Code § 17.44.005 and Gov. Code §§ 66310–66342.
How many ADUs can I build on a single-family lot in Monrovia?
Up to two ADUs plus a junior ADU. Monrovia Municipal Code § 17.44.005(D)(1) lets a single-family lot develop ADUs “pursuant to both” subsections — one ADU converted from existing space in the house or an accessory structure, and one new detached ADU of up to 800 sqft — and (D)(3) adds one JADU on top. That is the full stack state law requires under Gov. Code § 66323(a)(1)–(2), confirmed by the HCD ADU Handbook (March 2026, p. 17). The 2025 amendment wrote it into the local code, so you do not have to argue preemption to get there.
On a lot with an existing multifamily building, § 17.44.005(D)(2) allows conversion of non-livable space into at least one ADU up to 25% of the existing unit count, plus up to eight detached ADUs capped at the number of existing units (Gov. Code § 66323(a)(4)(A)(ii)).
How big can an ADU be in Monrovia?
It depends which of the two tracks you file under. Per Monrovia Municipal Code § 17.44.005(D)(1), the streamlined track allows a converted ADU with no maximum size and a new detached ADU of up to 800 sqft. The alternative-local-standards track at § 17.44.005(E)(2) allows one larger ADU: up to 1,000 sqft detached, or, attached, the lesser of 50% of the single-family dwelling or 1,000 sqft. The minimum unit size is 150 sqft.
Two state floors sit under all of it: Gov. Code § 66321(b)(2) bars any cap below 850 sqft for a studio or one-bedroom and 1,000 sqft with two or more bedrooms, and Gov. Code § 66321(b)(3) protects an 800-sqft unit regardless of floor-area or lot-coverage math. A JADU is capped at 500 sqft (Gov. Code § 66313(d)).
How tall can an ADU be in Monrovia?
A new detached ADU is capped at 16 feet, per Monrovia Municipal Code § 17.44.005(D)(1)(b)3. and (E)(4)(b) — the state floor in Gov. Code § 66321(b)(4)(A). The ordinance itself raises that to 18 feet where the lot is within one-half mile walking distance of a major transit stop or a high-quality transit corridor, plus an additional 2 feet to carry a roof pitch that matches the primary dwelling (Gov. Code § 66321(b)(4)(B)). On a multifamily lot, a detached ADU also gets 18 feet where it shares the lot with an existing or proposed multistory multifamily structure.
An attached ADU may reach 25 feet and two stories, or the zoning district’s height limit, whichever is lower (§ 17.44.005(E)(4)(a)) — though that clause cannot be applied to drop an attached ADU below the 25-foot state floor in Gov. Code § 66321(b)(4)(D). In practice, Monrovia is a single-story detached-ADU market.
Do I need to add a parking space for an ADU in Monrovia?
Usually not. Monrovia Municipal Code § 17.44.005(F)(2)(a) starts at one on-site space per ADU. It then lists ten exemptions that remove it. Among them: any ADU under the streamlined track. Any new ADU of up to 800 sqft with 4-foot side and rear setbacks. A lot within one-half mile walking distance of public transit. A lot in a historically significant historic district. An ADU inside the primary residence or an accessory structure. An on-street-permit area where the occupant is not offered a permit. A car-share vehicle within one block. That list tracks Gov. Code § 66322.
Converting or demolishing a garage, carport or covered space never triggers replacement parking (Gov. Code § 66314(d)(11)), and a city may not require parking for a JADU at all (Gov. Code § 66334(a)). Where a space is required it may be covered, uncovered or tandem, and in the front yard it is limited to the driveway and no more than 25% of the front yard.
Can I build an ADU on a historic property in Monrovia?
Yes — the rules are design standards, not a prohibition. Under Monrovia Municipal Code § 17.44.005(E)(5), an ADU on a national, state or local historic landmark, or on a contributor within a designated historic district, may not require a change to the street-facing facade, may not require demolition of a landmark, and must match the existing architectural features where the exterior changes. A property under a Mills Act contract follows the standards and conditions of that contract.
Those standards attach to the alternative-local-standards track. An ADU built under the streamlined track is expressly exempt from § 17.40.090, the City’s Certificate of Appropriateness section (§ 17.44.005(D)(4)) — which is why a rear-yard detached unit of up to 800 sqft is often the shortest road on a landmark lot. A historic-district lot is also exempt from the ADU parking requirement (§ 17.44.005(F)(2)(a); Gov. Code § 66322), and review stays ministerial either way (Gov. Code § 66317).
Does Monrovia require the owner to live on the property?
Not for an ADU. Monrovia Municipal Code § 17.44.005 imposes no owner-occupancy requirement on an ADU, which is what Gov. Code § 66315 requires — a city may not impose one. For a JADU, § 17.44.005(G)(4) does require the owner to live in the single-family dwelling containing the JADU, in either the remaining portion of the house or the JADU itself, with an exception for JADUs owned by a governmental agency, land trust or housing organization, and § 17.44.005(G)(5)(c) records that condition in a declaration of restrictions.
That text states the pre-2026 rule. AB 1154 amended Gov. Code § 66333(b) effective January 1, 2026, so JADU owner-occupancy may only be required where the JADU shares sanitation facilities with the primary dwelling. Give the JADU its own bathroom and the state rule controls.
Can I rent a Monrovia ADU on a short-term basis?
No. Monrovia Municipal Code § 17.44.005(G)(1) prohibits using an ADU as a short-term rental and requires every rental ADU to be rented for 30 consecutive days or more.
That is not a local preference: Gov. Code § 66323(e) requires a local agency to impose a rental term longer than 30 days on a § 66323 unit, and Gov. Code § 66333(g) does the same for JADUs. Nightly and weekly letting is out everywhere in California for these units. Month-to-month leases, annual leases and furnished mid-term tenancies are all unaffected.
Can I sell a Monrovia ADU separately from the main house?
No. Monrovia Municipal Code § 17.44.005(G)(2) bars conveying an ADU separately from the lot and the primary dwelling, except as provided in Gov. Code §§ 66340 through 66342 — which preserves the narrow state path for a unit built with a qualified nonprofit but goes no further, because the condominium route requires a local AB 1033 opt-in ordinance (Gov. Code § 66342) and Monrovia has not adopted one. A JADU may never be conveyed separately.
Among Los Angeles-area cities only a few have opted in, Santa Monica (SMMC § 9.31.026) and Culver City (CCMC § 17.400.096) among them. Build here for rental income, family housing or long-term value, not for a condominium exit.
Can I convert my garage into an ADU in Monrovia?
Yes, and it is often the least expensive route. Monrovia Municipal Code § 17.44.005(D)(1)(a) permits one converted ADU per single-family lot inside the existing or proposed house or an existing accessory structure, attached or detached, with no maximum size and an allowance of up to 150 additional sqft for ingress and egress on an accessory-structure conversion. Setbacks only need to be sufficient for fire and safety, and no replacement parking may be required for the stalls you lose (§ 17.44.005(F)(2)(a); Gov. Code § 66314(d)(11)).
A converted unit is also the one that stacks: under (D)(1) you may build it and a new detached ADU of up to 800 sqft on the same lot. An attached garage may instead be used for a JADU, because § 17.44.005(D)(3)(a) treats a structure attached to the residence as part of the single-family dwelling.
How long does an ADU permit take in Monrovia?
The City must approve or deny a complete ADU application within 60 days, and the review is ministerial — a building permit issued by the Director, with no public hearing and no discretionary design review (Monrovia Municipal Code § 17.44.005(B)(3), (D); Gov. Code § 66317). The City must also determine completeness and notify you in writing within 15 business days (SB 543, effective January 1, 2026; Gov. Code § 66317(a)(2)(A)).
On a pre-engineered Signature plan, expect roughly 2 weeks of plan preparation, a permit cycle measured in weeks rather than months, then 4 to 6 months of construction — about 6 to 9 months start to finish. Custom designs run longer at both ends because the City is reviewing the drawings for the first time.
What does an ADU cost in Monrovia?
Signature plan fees are fixed at $7,490 to $12,990, which includes architectural design and full permit processing. Building the unit with an independent licensed general contractor is estimated at roughly $180K–$420K across the lineup, depending on size.
City charges are separate. A conforming ADU is a ministerial building permit, and Monrovia’s building-permit and plan-check fees are valuation-based under the City’s adopted fee schedule. Confirm the current figures with the Planning Division before you budget. Monrovia charges no traffic impact fees on an ADU or JADU under Monrovia Municipal Code § 17.44.005(H)(2). A detached ADU may need its own utility meter, with a connection fee or capacity charge proportionate to the unit (§ 17.44.005(I)(3)).
Do I pay impact fees on a Monrovia ADU?
Not below 750 sqft. An ADU of 750 sqft or less pays no development impact fees anywhere in California (Gov. Code § 66311.5(c)(1)), and Monrovia Municipal Code § 17.44.005(H)(1) applies impact fees only as state law allows. Above 750 sqft, impact fees must be proportional to the primary dwelling’s size rather than charged flat per unit.
A JADU of 500 sqft or less is exempt as well, and an ADU or JADU under 500 sqft is not subject to school impact fees (Gov. Code § 66311.5, § 66311.5(c)(3)). Separately, § 17.44.005(H)(2) bars traffic impact fees on ADUs and JADUs under the City’s Chapter 3.22 unless that chapter is expressly amended. Utility connection and capacity charges are a different item and follow § 17.44.005(I).
Does Monrovia have pre-approved ADU plans?
Yes. The City runs a Pre-Approved ADU Plan Program for homeowners, published on the Monrovia Community Development pages — the local answer to the statewide pre-approval mandate of AB 1332 (Gov. Code § 65852.27), which required every city to have a program running by January 1, 2025.
A pre-approved plan is the fastest route across the counter, and it is built as filed. CALI ADU does not participate in the program: our Signature plans are individually permitted on your lot and adapted to its setbacks, grade, historic status and utility routing. If you want a standard plan built as-is on a simple lot, the City program is a real option worth looking at first.
My Monrovia garage was converted years ago without a permit — can I legalize it?
Often, yes. Gov. Code § 66311.7 sets up a streamlined path for an ADU or JADU built without permits before January 1, 2020. AB 2533 added it, and SB 543 renumbered it effective January 1, 2026. Under that section a city may not deny the permit over building-code violations unless they threaten health or safety.
Monrovia’s own ordinance runs in the same direction: Monrovia Municipal Code § 17.44.005(F)(7) says the City shall not deny an ADU or JADU application because of existing nonconforming zoning conditions, building-code violations or unpermitted structures that do not present a threat to public health and safety and are not affected by the construction. In an older housing stock like Monrovia’s that combination matters. Have the structure surveyed before you apply, because the health-and-safety carve-out is where these applications turn.
Official sources
Where the local chapter and state law differ, state law sets a floor the city cannot drop below (Gov. Code § 66316). After the 2025 amendment, Monrovia’s chapter mostly meets that floor in its own text rather than relying on preemption to get there.
| Source | What it governs |
|---|---|
| Monrovia Municipal Code § 17.44.005 (opens in a new tab) American Legal Publishing · section annotation reads “Ord. 2020-10 § 12, 2020; Ord. 2025-01 § 8, 2025” | The binding local ordinance: the streamlined and alternative tracks, unit counts, size and height caps, setbacks, the ten parking exemptions, the historic-resource standards, the JADU covenant, impact fees and utility connections. Every MMC citation on this page traces here. |
| City of Monrovia — Accessory Dwelling Units (opens in a new tab) monroviaca.gov · Community Development, Planning Division · includes the Pre-Approved ADU Plan Program (opens in a new tab) | The City’s own ADU guidance, the pre-approved plan program, application forms, and the current fee schedule for building permit and plan-check charges. |
| MMC Chapter 17.40 — Historic Preservation (opens in a new tab) American Legal Publishing · landmark and district designation, and the § 17.40.090 Certificate of Appropriateness | The chapter behind the historic layer: how a landmark or historic district is designated, and the review a streamlined-track ADU is expressly exempted from. |
| California Government Code §§ 66310–66342 (opens in a new tab) California Legislative Information · renumbered from former § 65852.2 et seq. by SB 477, eff. March 25, 2024 | State ADU law — the floor every city must meet. Source for the 60-day ministerial clock, the owner-occupancy and parking preemptions, the 800 sqft entitlement, the impact-fee exemption, and the § 66323 unit stack. |
| HCD ADU Handbook (opens in a new tab) California Department of Housing and Community Development · updated March 2026 | The state’s official interpretation of ADU law, and the position that controls when a local rule reads more narrowly. The units-per-lot answer on this page comes from its worked example at p. 17. |
| HUD FY 2026 Fair Market Rent Schedule (opens in a new tab) huduser.gov · Los Angeles–Long Beach–Glendale, CA HMFA — a market benchmark, not a regulation | The only rent figures on this page. Metro-wide fair market rents by bedroom count, used as a published floor rather than a projection for your specific street. |
Last verified against primary sources on August 24, 2026. California amends ADU law every January 1, and Monrovia amended its own chapter in 2025. 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.
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