Brea ADU Regulations

32 min read

Planning an ADU in Brea? Start with the correct reviewing agency, compare the rules for your project and understand what to confirm before investing in drawings.

Brea local area

TL;DR: Brea ADU Regulations

An accessory dwelling unit is an independent home on the same parcel as a primary residence. It needs permanent living, sleeping, cooking and sanitation facilities. In Brea, the first design decision is which approval pathway fits your property: a new detached building, an attached addition, a conversion, a junior ADU or a qualifying multifamily project.

California’s ADU law protects certain sizes, heights, setbacks and approval procedures. Those protections do not make every floor plan suitable for every lot. Existing buildings, fire safety, utilities, easements, topography and the property’s jurisdiction still matter. A useful feasibility review puts the rules on a measured site plan before choosing finishes or assuming a construction price.

  • Check the jurisdiction first. Confirm the property is within the city, then use its current application instructions. Nearby jurisdictions can have different submission processes.
  • Four-foot side and rear setbacks are an important starting point for new ADUs. Qualifying conversions and same-location replacements have different setback protections.
  • An eligible 800 sq ft ADU has strong state protections. The 850 and 1,000 sq ft figures are protections against restrictive local size caps, not universal maximums.
  • A JADU is limited to 500 sq ft. Its kitchen, bathroom, ownership and location requirements differ from an ordinary ADU.
  • Parking is often exempt, but the reason matters. Transit access, conversion status and other statutory conditions need to be checked for the actual proposal.
  • The 60-day review period starts with a complete application. It is not a promise that design, utility upgrades and construction will finish in two months.
  • Under the 2026 fee provision, an ADU of 750 sq ft or less is exempt from impact fees. This does not eliminate every permit, utility or school-related charge.

This guide distinguishes state protections from project-specific decisions. It is dated November 6, 2026; confirm the rules applicable to your submission before relying on a dimension or deadline. Source links throughout the guide identify the relevant statutes and city agencies.

Essential ADU rules for Brea

What you can build

Item Rule to start with Important distinction
New detached ADU Confirm the applicable local maximum and state protections with Planning. The separate state-exempt single-family detached pathway may be limited to 800 sq ft. Do not apply one pathway’s limit to every conversion or multifamily proposal.
Protected local size caps A local maximum cannot be below 850 sq ft, or 1,000 sq ft for an ADU with more than one bedroom. These are minimum allowances for local maximums, not a promise that every project can use every part of a lot.
Side and rear setbacks New construction generally cannot be required to exceed four feet under the applicable ADU provisions. Existing-space conversions and qualifying replacements can have no new setback requirement; building and fire safety still apply.
Height Detached height protections start at 16 feet, with 18-foot allowances in specified cases. Transit proximity, a multistory multifamily site, roof alignment and attached construction change the analysis.
Junior ADU Maximum 500 sq ft within the qualifying single-family residence. An attached garage can be included; a detached backyard structure is not the ordinary JADU pathway.
Permit review Complete applications generally receive an approval or denial within 60 days under state law. Completeness review, applicant delays, a new primary dwelling and other statutory conditions affect the clock.

Read these rules together with Government Code 66314, 66321, 66323 and 66333.

The three numbers homeowners often confuse

750 sq ft concerns an impact-fee exemption in the 2026 statute. 800 sq ft appears in important development-standard protections and the state-exempt detached pathway. 850/1,000 sq ft describe protections against restrictive local maximums, depending on bedroom count. These numbers answer different questions. A design should not be reduced or enlarged simply because one number appears on an online checklist.

For example, a homeowner comparing a 750 sq ft unit with an 800 sq ft unit should assess the extra usable space, the fee treatment and the applicable approval route separately. Neither size guarantees a low construction cost. A shorter utility run, a straightforward foundation and a workable access route can matter as much as a small difference in floor area.

Confirm your property jurisdiction

This guide covers property within the City of Brea. Confirm the parcel number and municipal boundary before selecting the application. A mailing address, nearby office or neighboring project does not establish the reviewing agency.

What matters locally in Brea

Brea’s ADU chapter distinguishes new construction from qualifying conversions. Its setback provisions include four-foot side and rear treatment and a safeguard against a front setback blocking an eligible 800 sq ft ADU. The relevant approval category and safety requirements still matter. See Brea ADU code and Brea planning applications.

How should I handle a corner lot?

Have Planning identify which property lines are front, street-side and rear for the proposal. Draw those designations and setbacks on the site plan. Do not assume the side with the driveway is the legal front or apply an interior-lot diagram without checking.

Compare placement before maximizing area

Try layouts that preserve a usable entrance and outdoor space for both households. Show how residents, utilities and construction access reach the unit. An efficient position may be more useful than adding floor area in the most constrained corner.

What should I bring to the initial property review?

Bring the parcel number, available surveys, permit records, existing drawings and photographs of the house, yard, garage and access route. Mark known utility equipment, grade changes and easements. Explain who will use the ADU and whether you are considering a conversion, addition or detached unit.

A fence is not proof of a legal boundary. A title report and measured site information answer different questions. Establish both before selecting a footprint, and keep agency responses with the project records.

How many ADUs can you build?

The answer depends on the existing residential configuration and the statutory pathway. A single-family lot and an existing multifamily property do not have the same unit-count rules. California Government Code 66323 provides specific approval categories and allows qualifying combinations. That is why a blanket statement such as “one ADU per property” can be misleading.

What can qualify on a single-family lot?

Section 66323 includes a conversion ADU and a JADU within qualifying proposed or existing residential space, or qualifying existing accessory space for the ADU. It also provides a new detached ADU pathway that a local agency may limit to 800 sq ft. The statute permits qualifying categories to be combined; each proposed unit must satisfy the conditions of its own category.

This does not mean every small lot can physically accommodate every possible combination. Identify the primary dwelling, existing accessory structures and any existing ADU or JADU. Then draw the proposed configuration and check independent access, building safety and services. Ask the reviewing agency to confirm the unit-count basis for the actual site rather than relying on an unlabeled diagram.

What changes for an existing multifamily property?

Qualifying nonlivable portions of an existing multifamily structure can be converted into ADUs under section 66323. The statute requires at least one such conversion allowance and allows up to 25 percent of the existing multifamily dwelling units, subject to the pathway’s conditions. Examples of potentially eligible spaces include storage areas or garages; occupied living space is a different question.

The detached pathway for an existing multifamily site allows up to eight detached ADUs, but no more than the number of existing units on the lot. For a lot with a proposed multifamily dwelling, the corresponding detached allowance is up to two. These are different categories, so do not apply the eight-unit figure to every property described casually as a duplex or apartment site.

Before estimating rental income from several new units, establish the legal number and type of existing dwellings. A converted room, an assessor entry and a permitted dwelling are not automatically equivalent evidence. The design team should document the proposed pathway for each new unit and resolve any uncertainty with the city.

Source: Government Code 66323, state-exempt ADU categories and combinations.

ADU size, height and design limits

How large can the ADU be?

The correct size allowance in Brea depends on the approval pathway, current local standards and state protections. Do not assume a 1,200 sq ft plan advertised for another city is automatically permitted here. Review the proposed bedroom count, interior livable area and applicable local maximum with Planning. For attached units, a percentage of the main house cannot be used in isolation from state size protections.

Local maximum-size limits cannot fall below 850 sq ft, or 1,000 sq ft when an ADU has more than one bedroom. Separate protections prevent certain floor-area, lot-coverage, open-space, front-setback and minimum-lot-size requirements from blocking an eligible 800 sq ft ADU with compliant height and four-foot side and rear setbacks. The precise approval category remains important.

Does a small primary house force me to build a tiny attached ADU?

Not necessarily. The 50 percent attached-unit provision must be read with the protections in section 66321. For example, simply calculating half of a 1,000 sq ft house and declaring a 500 sq ft maximum ignores the statutory protections against overly restrictive local size limits. Have the applicable sections and proposed bedroom count identified in the planning review.

An attached addition also changes the original building. Structure, roof connections, fire separation and existing openings may influence the practical design. A protected size allowance is a planning rule, not a guarantee that a particular attachment point is straightforward or economical to build.

How tall can it be?

For detached ADUs, state height protections begin at 16 feet. An 18-foot allowance applies within one-half mile walking distance of a major transit stop or high-quality transit corridor, as defined by the statute. That transit category also includes an additional two feet to accommodate a roof pitch aligned with the primary dwelling. Another 18-foot protection applies on a lot with an existing or proposed multistory multifamily building.

For an attached ADU, the protected height allowance is 25 feet or the primary dwelling’s applicable zoning height limit, whichever is lower. This does not require a local agency to allow more than two stories. These figures describe limits on how restrictive local standards may be, not a single citywide promise that every ADU can be built to that height.

Can I assume a nearby bus stop permits a taller ADU?

No. The transit definitions used for height and parking are not identical. The height provision references a major transit stop or high-quality transit corridor and a walking-distance test. A parking exemption uses its own statutory conditions. Confirm the qualifying transit facility and walking route for each claimed benefit.

Put the supporting information in the project file. A straight line on a map can overlook an inaccessible route or physical barrier. The building’s roof design, the primary house and any applicable safety requirements should be reviewed before using the additional height in a final layout.

Sources: Government Code 66314 and 66321.

Setbacks, placement and access

Side and rear setbacks are distances from legal property lines, not from the nearest fence, hedge or neighboring building. Under the applicable state ADU provisions, new construction generally cannot be required to have side or rear setbacks greater than four feet. An existing-space conversion or a qualifying replacement in the same location and dimensions has a different protection against new setback requirements.

That distinction is particularly useful for garages built closer to a boundary than a new structure would normally be placed. It does not remove the need to examine wall construction, openings, eaves and fire safety. A building can have a protected location while still requiring changes to become a lawful dwelling.

Does a zero-setback conversion mean I can add windows on the boundary?

No. Setback relief and building-code requirements answer different questions. Retaining a garage footprint does not automatically authorize a new window, door or roof projection near a property line. Have the design show the existing walls, proposed openings and required construction assemblies together.

This is also why a generic floor plan may not work when mirrored onto a tight lot. A bedroom window placed on the wrong wall can create a major design problem. Solve ventilation, light, emergency escape where applicable and privacy as part of the conversion layout, not after the room arrangement is fixed.

Can the ADU go in the front yard?

Do not assume either a universal prohibition or unrestricted permission. Section 66321 prevents certain front-setback requirements from precluding an eligible 800 sq ft ADU, but that protection operates within a specific statutory framework. The proposed placement still needs a property-specific review of access, safety, utilities and the qualifying pathway.

A front-yard option may also compete with the existing entrance, driveway or service equipment. Compare it with other arrangements on the site. The most useful question is which compliant location delivers a workable home and preserves safe access, rather than which corner looks empty in an aerial photograph.

What about distance between buildings?

Building separation, wall ratings, openings and fire requirements depend on the project. Show actual distances between the house, ADU and other structures, then resolve the applicable requirements with the design and reviewing teams. A property-line setback is not the same measurement as separation between two buildings.

State law also says an ADU cannot be required to have a “passageway” as defined in the ADU statute. That does not mean physical access, emergency considerations or utility maintenance can be ignored. Plan a usable route to the dwelling and consider how construction materials, waste and equipment will reach the work area.

Sources: Government Code 66314, setbacks and passageways and 66321, protected development standards.

Parking rules and exemptions

Parking should be checked early, but it is not automatically a barrier to an ADU. Where parking can be required, the state framework caps the requirement at one space per unit or bedroom, whichever is less. Tandem parking may be permitted under the statute. Several exemptions can eliminate the ADU parking requirement altogether.

Section 66322 includes exemptions for an ADU within one-half mile walking distance of public transit, an ADU within a qualifying historic district, and an ADU that is part of the proposed or existing primary residence or an accessory structure. It also covers circumstances involving unavailable on-street permits, a car-share vehicle within one block and specified concurrent primary-dwelling applications.

Must I replace parking when converting a garage?

State law says replacement off-street parking cannot be required when a garage, carport, covered parking or uncovered parking is demolished or converted in conjunction with an ADU. Keep the distinction clear: removal of existing parking and a requirement for new ADU parking are related but separate questions, both addressed by the statute.

A driveway still has practical uses. Think about deliveries, accessible circulation, refuse storage and the residents’ actual transportation needs. Choosing to retain a useful parking space is different from accepting a requirement that the applicable law does not permit.

What proof should support a parking exemption?

Identify the exact exemption and provide the information needed to establish it. For transit, record the qualifying stop and walking route. For a conversion, show the existing structure and proposed scope. If relying on permit-parking conditions or car share, verify those circumstances rather than assuming they apply throughout the neighborhood.

A written parking note on the site plan helps prevent different reviewers or consultants from making conflicting assumptions. If the project changes from a conversion to a substantially different new building, revisit the exemption rather than carrying the original conclusion forward automatically.

Sources: Government Code 66322, parking exemptions and 66314, parking limits and replacement parking.

Interior requirements and junior ADUs

An ordinary ADU must function as an independent dwelling. A spare bedroom with a bathroom is not automatically an ADU, and a backyard office is not automatically approved for residential occupancy. The plans need to establish the facilities and building conditions required for the proposed use.

For everyday design, consider how someone will cook, sleep, store belongings, move through the home and use the bathroom. A technically large floor area can still produce an awkward dwelling if circulation consumes too much space. Conversely, a compact unit can work well when the kitchen, bathroom and entry are coordinated rather than added as afterthoughts.

How is a JADU different from an ADU?

A junior ADU is limited to 500 sq ft and is created within the walls of a qualifying single-family residence; an attached garage is included in the statutory framework. It needs a separate entrance and an efficiency kitchen with cooking appliances, preparation space and storage. A JADU may share sanitation facilities with the main residence under the applicable conditions.

When sanitation is shared, the statute requires an interior entry to the main living area. A JADU also carries a recorded deed restriction addressing separate sale and its required characteristics. It should be selected because the arrangement fits the household and property, not simply because the name sounds like a smaller detached ADU.

Must the owner live on the property?

Ordinary ADUs are not subject to an owner-occupancy requirement under section 66315. The 2026 JADU statute makes a more specific distinction: owner occupancy is required when the JADU shares sanitation facilities with the existing structure, subject to the listed ownership exceptions. A JADU with its own sanitation facilities does not carry that same owner-occupancy requirement under section 66333.

Do not rely on an older checklist saying every JADU always requires owner occupancy. Review the current statute, the proposed bathroom arrangement and the recorded restrictions that will apply. If future rental or sale flexibility matters to you, resolve those obligations before committing to the JADU design.

Does building an ADU force sprinklers into the existing house?

The state ADU framework says sprinklers are not required in the ADU if they are not required for the primary residence, and ADU construction does not itself trigger sprinklers in the existing primary dwelling. The project still needs a review of its actual building and fire conditions.

Avoid treating that protection as a general exemption from all fire-safety measures. Wall assemblies, openings, alarms and other applicable requirements are separate subjects. Explain any concurrent work on the primary dwelling so the reviewing team can distinguish ADU-related work from a broader alteration project.

Sources: Government Code 66313, definitions, 66315, 66333, JADU requirements and 66314, sprinklers.

Garage conversions and unpermitted units

A garage conversion can reuse an existing footprint, but the existing building must be understood before the design is priced. Review foundations, framing, roof condition, drainage, floor levels, utility service and the proposed openings. A garage designed to store vehicles may need substantial work to function as comfortable residential space.

Separate the question “Can this footprint qualify?” from “What must be rebuilt?” A protected setback does not establish the condition of a slab. A finished-looking room does not establish that residential work was permitted. Existing records and a physical assessment should inform the scope together.

Can I extend an existing conversion?

Under the section 66323 conversion category, an expansion of up to 150 sq ft beyond the existing accessory structure’s dimensions is permitted only for accommodating ingress and egress. It is not a general allowance to add 150 sq ft of bedroom or living space under that conversion provision.

If you want a larger addition, investigate the appropriate alternative or combined scope instead of labeling all new construction a conversion. Draw the existing and proposed footprints distinctly. That makes the setback, structural and size analysis more transparent and helps avoid a late disagreement about the project’s approval category.

What if the existing ADU was never permitted?

Government Code 66311.7 provides a specific pathway for unpermitted ADUs and JADUs constructed before January 1, 2020. It limits denial based on certain building or ADU-standard violations, while retaining health-and-safety protections and excluding buildings deemed substandard under the referenced law. The construction date and existing conditions therefore matter.

The statute also describes confidential third-party inspection before application and limits certain fees for qualifying legalization projects. This is not an automatic certificate of occupancy or a promise that no corrective work will be needed. Gather evidence of the unit’s age and condition, then establish the correct legalization process with the city.

Sources: Government Code 66323, conversion category and 66311.7, pre-2020 unpermitted units.

Slopes, easements and property constraints

Review slopes, easements, drainage, fire requirements and access before selecting a building footprint. The importance of each item depends on the parcel; a regional description is not a substitute for site investigation.

Does a sloped property rule out an ADU?

Not automatically. It changes the investigation and potentially the design. Measure the grade and discuss foundation support, drainage, retaining walls and construction access with the appropriate professionals. An attractive flat-looking corner in a photograph is not enough information to establish a buildable pad.

A standard design may have site assumptions that do not match a sloping lot. That mismatch does not automatically prevent a custom ADU. Ask which design route and supporting investigations fit the property before purchasing plans.

What should I check about easements and utility access?

Locate recorded easements and compare them with the proposed building, foundation, overhangs, access and service trenches. Ask the responsible agency or utility provider to resolve conflicts before drawings are finalized. An ADU setback allowance does not cancel another party’s recorded access rights.

Also locate equipment that needs ongoing maintenance. A design that physically fits between property lines may still block a meter, cleanout, drainage route or service access. Put that information on the site plan rather than leaving it as a note for the contractor to discover later.

Can an HOA simply prohibit the ADU?

California provides protections against unreasonable restrictions on qualifying ADUs and JADUs, but private approval and city review are not the same process. Obtain the applicable documents and identify any requested architectural review early. Do not assume either that an HOA can ban any proposal or that all private requirements disappear.

Keep records of the requested changes and have any disputed restriction assessed against current law. The design should remain coordinated across the city submission and any applicable private review.

Sources: Brea ADU code and HCD’s March 2026 ADU handbook.

Permits, review deadlines and standard plans

Start with Brea ADU code for the local application route. Confirm the latest intake checklist, the responsible reviewing departments and whether the proposed project has a standard-plan option. A design approved elsewhere is not automatically pre-approved here.

Completeness and approval are different milestones

State law provides a 15-business-day completeness determination and generally a 60-day approval-or-denial period for a complete qualifying application with an existing dwelling. These are different clocks. They do not promise that surveying, design, corrections, utility work and construction will finish within 60 days.

Keep submission receipts, completeness notices and correction responses together. A proposal with a new primary dwelling or an applicant-requested delay can have different timing provisions. Record the actual application milestone rather than treating the review period as a complete-project guarantee.

What should I confirm before buying a standard plan?

Ask whether the exact design is currently approved by the reviewing agency, which code edition it uses and who owns the drawings. Obtain a written scope for site adaptation, foundation work, engineering, energy documentation and permit responses. A downloadable plan is not necessarily an approved plan.

Our floor-plan collection is a design reference. Do not assume a Uni Construction plan is listed in a local pre-approved program unless that specific approval has been established. Plan rights, permit approval and construction services are separate parts of the project.

What happens after a correction notice?

Assign each comment to the relevant designer or consultant and prepare a coordinated response. Identify the revised sheets and explain how each issue was addressed. If the footprint or building systems change, check all affected drawings rather than correcting only the sheet named in the comment.

A revised plan should remain consistent with the site information, energy documentation and structural design. Keep earlier versions for the project record but clearly identify the current submission so the contractor does not price or build from superseded drawings.

Keep the permit scope coordinated

The site plan, floor plan, elevations, structure and utilities should describe one consistent proposal. Identify any separate permits or agency approvals that apply. Confirm who obtains those approvals and which must be resolved before construction or final occupancy.

Source: Government Code 66317, application review. Local intake reference: Brea planning applications.

ADU fees, utilities and construction budgeting

A useful budget separates design and documentation, agency fees, utility work, site preparation and building construction. These categories respond to different conditions. Avoid comparing a contractor’s building-only figure with another estimate that includes engineering, service upgrades and difficult site work.

What is the impact-fee exemption?

Government Code 66311.5, effective in 2026, exempts an ADU with 750 sq ft of interior livable space or less from impact fees. A JADU with 500 sq ft or less is also covered. For an ADU larger than 750 sq ft, the statute provides proportional impact-fee treatment in relation to the primary dwelling’s square footage.

“Impact fee” is a defined category. The exemption does not mean that plan-check fees, building permits, utility connections and every other charge disappear. The statute expressly distinguishes utility connection fees and capacity charges. Request an itemized agency estimate and identify the legal basis for each charge rather than relying on a single total called “permit fees.”

Do conversions need separate utility connections?

For the qualifying conversion category in section 66323(a)(1), section 66311.5 protects against a required new or separate direct utility connection and related connection or capacity charges, subject to stated exceptions such as construction with a new single-family dwelling or specified separate conveyance. Other ADU categories can be treated differently.

This does not establish that existing pipes, service equipment or electrical capacity can support every proposed design without work. Ask the relevant utility and project team to evaluate capacity and routing. Distinguish a legal connection requirement from the physical improvements needed to make the proposed installation function safely.

What makes two similar-sized ADUs cost differently?

Important variables include the foundation approach, existing structure condition, access, utility routes, finish selections and the amount of work to the primary property. A conversion with substantial structural repair can have a different cost profile from a straightforward new building. The floor area alone cannot settle that comparison.

Request a scope that identifies assumptions, exclusions and unresolved items. Ask who handles design, engineering coordination, permit responses, utility coordination and inspections. Comparing those responsibilities helps you evaluate proposals fairly and reduces the risk of discovering missing work after selecting a contractor.

Source: Government Code 66311.5, fees and utility connections. Current project charges should be confirmed with the responsible agencies and providers.

Renting, ownership and future use

Decide how the ADU will be used before finalizing the design. Housing a parent, accommodating an adult child and operating a rental can lead to different priorities for privacy, storage and circulation. Those choices do not replace the legal requirements, but they help produce a home that fits the intended resident.

The state-exempt ADU categories in section 66323 and the JADU provisions require rental terms longer than 30 days. Other applicable local restrictions must also be checked. Do not treat an ADU permit as authorization for vacation-rental use or project short-term-rental income without separately establishing legality.

What should I resolve before renting the ADU?

Confirm final permit sign-off, lawful occupancy, the rental term and any applicable registration or operating obligations. Coordinate the lease, insurance, maintenance access and utility arrangement. An approved design is not the same milestone as a completed dwelling ready for tenants.

If the unit is intended for a family member first and a tenant later, design for that future change. Separate access, privacy, storage and service arrangements are easier to plan now than retrofit after occupancy. Check the rules that apply to the Brea property rather than transferring a neighboring jurisdiction’s rental requirements.

Can the ADU be sold separately from the main house?

Do not assume so. The ordinary ADU framework generally ties the unit to the primary property, while separate conveyance is addressed through specific statutory mechanisms and conditions. A JADU deed restriction includes a prohibition on sale separate from the single-family residence. An ordinary building permit is not a subdivision approval.

If separate ownership is essential to your plans, identify the currently available local process and required legal work before designing around that goal. This guide does not represent that Brea has approved a particular separate-sale pathway for your parcel.

Sources: Government Code 66323, 66333 and 66342.

Choosing a design route for Brea

Start with the existing property and the household’s needs. A custom design, an existing-space conversion and an available standard plan solve different problems. Compare them using the same scope, including site work and the documents needed for approval.

Decision Custom design Standard plan, if available
Layout Developed around the household and property. Begins with a specific existing design.
Site fit Investigated for the proposed footprint. Must be checked against the plan’s assumptions.
Changes Coordinated through the design process. May require new review or affect approval status.
Permit Requires a complete project submission. Still requires property-specific approval.
Pricing Depends on the agreed design and construction scope. Plan purchase is only one part of the total.
How do I compare proposals fairly?

Ask each provider to identify drawing rights, design revisions, structural work, energy documentation, agency responses and site adaptation. Keep construction pricing separate enough to see what is included. Compare allowances and exclusions, not just the amount on the first page.

If an existing structure will be reused, identify the evidence supporting that assumption. If a standard plan is proposed, identify its current approval and site requirements. The more specific these assumptions are, the easier it is to understand the practical difference between proposals.

Can I combine the ADU with work on the main house?

Discuss the full scope before applying. Ask the reviewing agency how related work should be submitted and whether separate permits are necessary. Coordinating the design can be useful, but a new ADU does not automatically authorize unrelated remodeling or resolve earlier unpermitted work.

Plan the construction sequence around access, utilities and any occupied rooms. Document which work belongs to each permit so inspections and final approvals can be tracked clearly.

Brea ADU regulations comparison chart

Use these three comparisons together. The first identifies the project pathway, the second covers dimensions and site rules, and the third addresses approvals and ongoing obligations. The tables adjust to your screen so you can compare the rules together. Each rule includes its qualifying condition and a direct source so you can check the provision behind the summary.

Scope: City of Brea planning guide, checked November 6, 2026. State protections are identified below; property-specific local and building requirements still need review. “Protected allowance” means a limit on how restrictive a local standard may be, not automatic approval of a particular design.

Compare the approval pathways

Project pathway Size or unit allowance What changes the answer Source
New detached, general ordinance route Confirm the local size cap and state protections for the bedroom count. Apply the relevant local standards with state protections; do not confuse this with the separate 800 sq ft exempt route. 66314
New detached, state-exempt single-family route Local agency may impose an 800 sq ft limit on this category. Four-foot side/rear setbacks and the applicable protected height; qualifying combinations are addressed in the statute. 66323(a)(2)
Attached addition General framework includes 50 percent of existing primary floor area. Read with the 850/1,000 sq ft local-cap protections and eligible 800 sq ft safeguard. The percentage alone is not the answer. 66321
Existing-space conversion Qualifying space within a residence or existing accessory structure. Separate access and safety conditions; up to 150 sq ft expansion only for ingress/egress under this category. 66323(a)(1)
Junior ADU Maximum 500 sq ft; one qualifying JADU under the single-family pathway. Within the residence, including attached garage; efficiency kitchen, separate entry and deed restriction. 66333
Existing multifamily, nonlivable-space conversion At least one; up to 25 percent of existing multifamily dwelling units. Qualifying nonlivable portions of the existing structure must satisfy dwelling building standards. 66323(a)(3)
Existing multifamily, detached units Up to eight, but no more than the existing unit count. Apply the detached category’s height, setback and other qualifying conditions. 66323(a)(4)
Proposed multifamily, detached units Up to two under this category. Do not substitute the existing-multifamily eight-unit allowance. 66323(a)(4)

Compare dimensions, placement and parking

Topic Rule or protected allowance Exception or qualification Source
Local maximum-size cap Cannot be below 850 sq ft, or 1,000 sq ft for more than one bedroom. These are minimum allowances for a local maximum, not universal project maximums. 66321
800 sq ft safeguard Certain size, lot-coverage, floor-area, open-space and front-setback standards cannot block an eligible unit. Applicable height and four-foot side/rear setbacks still matter. 66321(b)(3)
New side/rear setbacks No greater than four feet under applicable ADU provisions. Do not interpret property-line setbacks as a universal building-separation rule. 66314(d)(7)
Conversion setbacks No new setback for qualifying existing space or same-location, same-dimension replacement. Fire safety, wall construction and openings still require review. 66314(d)(7)
Detached height, baseline 16-foot protected allowance. Other categories or less restrictive local rules may allow more. 66321(b)(4)
Detached height, qualifying transit 18 feet, plus two feet for specified roof-pitch alignment. Within half-mile walking distance of the defined major stop or high-quality corridor. 66321(b)(4)
Detached height, multistory multifamily site 18-foot protected allowance. Existing or proposed multifamily dwelling must be multistory. 66321(b)(4)
Attached height 25 feet or primary-dwelling zoning height limit, whichever is lower. State protection does not require allowing more than two stories. 66321(b)(4)
ADU parking, when required At most one space per unit or bedroom, whichever is less. Statutory exemptions can remove the requirement; tandem provisions apply. 66314(d)(10)
Parking exemptions Transit, qualifying historic district, conversion and other listed circumstances. Check the exact exemption; parking and height transit tests differ. 66322
Replacement parking Not required when parking is removed or converted in conjunction with an ADU. Document the existing parking and proposed ADU scope. 66314(d)(11)

Compare permits, fees and use requirements

Topic Current rule What to confirm for your project Source
Application completeness 15 business days for the statutory completeness determination. Submission date, missing-item notice and resubmission history. 66317
Permit decision Generally 60 days from a complete application with an existing dwelling. New-primary-dwelling provisions and applicant-requested delays. 66317
Impact fees ADU of 750 sq ft or less exempt; JADU of 500 sq ft or less exempt. This is not an exemption from all permit and utility charges. 66311.5(c)
Larger-ADU impact fees Proportional to ADU area relative to the primary dwelling. Itemized charge categories and the applicable calculation. 66311.5(c)
Conversion utility connections Qualifying conversion category protected from a required separate direct connection and related charges. New-primary and specified separate-conveyance exceptions; actual service capacity. 66311.5(d)
Owner occupancy, ordinary ADU No owner-occupancy requirement under the state provision. Do not apply JADU-specific restrictions to an ordinary ADU. 66315
Owner occupancy, JADU Required when sharing sanitation, with statutory exceptions. Own-sanitation JADUs have different treatment in the 2026 statute. 66333
Rental term Longer than 30 days for section 66323 units and JADUs. Applicable local rental restrictions and occupancy approvals. 66323 / 66333
Local intake Confirm the current application route. Use the correct agency and current checklist for the parcel. Local guidance
Pre-2020 unpermitted unit Specific legalization protections and health-and-safety conditions. Construction date, existing condition and correct application route. 66311.7
Standard plans Establish current approval of the exact design, if available. Site fit, foundation, plan rights and requested changes still need review. Local reference

From the first sketch to a completed ADU

1. Establish the property facts

Confirm jurisdiction, existing permitted dwellings, the proposed unit type and the site’s known constraints. Collect records before assuming that an existing garage or room can be reused exactly as it stands. The goal is a documented starting point that everyone on the project understands.

2. Compare practical layouts

Evaluate the footprint, resident needs, access, privacy and utility routing together. Compare alternatives using the same scope assumptions. A useful design review explains what each option changes, including whether it uses a different approval pathway or requires more work to the primary house.

3. Coordinate the application

Prepare a consistent drawing set and the supporting documents required for the project. Track agency submissions, completeness notices and correction responses. Keep proposed changes coordinated across architectural, structural and building-system information so one correction does not create a conflict elsewhere.

4. Confirm the construction scope

Before construction, align the permitted design with the contract, exclusions, selections and schedule. Identify unresolved utility work and site conditions. Confirm who manages inspections and documentation. A clear scope helps distinguish a genuine change requested by the owner from work that was always necessary but omitted from an estimate.

5. Complete inspections and operating checks

Follow the required inspections and obtain the applicable completion documentation before occupancy. If the ADU will be rented, address registration and operating requirements separately. Keep approved drawings, inspection records, warranties and equipment information together for future maintenance or property transactions.

Questions to bring to your ADU consultation

Can you tell me the maximum size from my address alone?

An address starts the review, but reliable advice also depends on records, existing buildings and the proposed pathway. A preliminary conversation can identify likely options and missing information. A measured, coordinated feasibility review is what turns those possibilities into a design basis.

Bring your priorities as well as your desired square footage. An extra bedroom, easier access for a parent or separation from the main yard may be more valuable than maximizing area. Uni Construction can use those goals to frame the design and construction questions that need answers next.

Should I choose an ADU type or a floor plan first?

Start with the property and the type of project it can reasonably support. Then compare floor plans that fit that pathway. Selecting a detached plan before discovering that the practical option is a garage conversion usually creates avoidable redesign.

Our ADU types guide explains the basic differences. The regulations on this page help you understand why those differences affect size, placement and approval. Use both alongside a site review rather than treating either as a parcel-specific approval.

What information helps you estimate the next stage?

Share the address, available records, photographs and your intended use. Tell us about known site issues and any target budget or timing constraints. Identify whether you need design, engineering coordination, construction or a coordinated scope covering several stages.

The first discussion should clarify what is known, what still needs investigation and what service is appropriate next. You can book a 30-minute consultation to discuss those decisions with Uni Construction.

Official sources and review notes

This guide separates state protections from local application information and property-specific design decisions. Reviewed November 6, 2026. Older summaries may not reflect later state changes. Where documents differ, ask the reviewing agency to identify the controlling provision for the proposed approval category.

For another property, choose its own guide from all 23 local ADU regulation guides. For design and construction support in this area, see our Brea services. A nearby project can be useful inspiration, but it does not establish the rules for your parcel.

Plan your next step

Talk through your address, existing space and goals with Uni Construction.

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