Building an ADU in Manhattan Beach. Rules, costs, timeline.

Can I build an ADU in Manhattan Beach?

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 projects here.

How many units a lot allows

MBMC § 10.74.050(B)(1)(a) allows a maximum of two ADUs on a lot with a proposed or existing single-family dwelling, of which only one may be detached. A junior ADU sits on top of that under § 10.74.060. Three separate things can therefore exist on one single-family lot.

• An ADU carved out of existing space. Inside the house or an accessory building, with up to 150 extra square feet for ingress and egress.
• A junior ADU. Up to 500 square feet, entirely within the single-family home (Gov. Code § 66313(d)).
• A new detached ADU. Up to 800 square feet on the streamlined track, with 4-foot side and rear setbacks.

That matches what Gov. Code § 66323(a)(1)–(2) requires and what the HCD ADU Handbook confirms. Most South Bay ordinances still read as one ADU plus one junior ADU and have to be corrected against the statute. Manhattan Beach fixed its own text in 2025, which is a genuine advantage when you file.

Multifamily lots

MBMC § 10.74.050(B)(1)(b) adopts Gov. Code § 66323(a)(3) and (4) directly rather than writing a narrower local number. On a lot with an existing multifamily building that means conversions of non-livable space — storage, boiler rooms, passageways, attics, basements, garages — equal to 25 percent of the existing units with a minimum of one, plus up to eight detached ADUs or the number of existing units, whichever is less (Gov. Code § 66323(a)(4)(A)(ii), as raised by SB 1211 effective 1 January 2025). A proposed multifamily building gets up to two detached units. Junior ADUs are a single-family product only.

Owner-occupancy

You do not have to live on the property to build an ADU here. The covenant Manhattan Beach requires under MBMC § 10.74.050(A)(3)(a) covers a rental term of 30 days or longer, no separate conveyance unless state law requires it, ongoing maintenance, and penalties for violation. Owner-occupancy is not on that list, and Gov. Code § 66315 would bar it if it were.

Junior ADUs are the exception, and the local text is now behind the statute. MBMC § 10.74.060(F)(i) requires the owner to occupy either the house or the junior ADU unless the owner is a government agency, land trust or housing organization, and Table 1 of the City’s Handout repeats it. Ord. 25-0004 took effect eight months before AB 1154 changed the rule.

What an ADU costs in Manhattan Beach (2026)

Plan pricing does not vary by neighborhood, and it does not vary by whether the lot is inside the Coastal Zone. The fee covers architectural design, structural engineering, Title 24 energy compliance, and every piece of permit processing and plan check correspondence through to an issued permit. Once the plans are permitted you arrange construction — build it yourself, bring your own licensed contractor, or build with one of our vetted partners.

The build estimate covers labor and materials, interior finishes, cabinetry, countertops, flooring, fixtures, appliances and utility connections. What sits outside it: City permit, plan check, water and sewer fees, any coastal permit fee where one applies, and site-specific work such as grading on the sloping blocks of the Hill Section, retaining walls, shoring on a walk-street lot, long utility runs or drainage. We identify and price all of that in the proposal before you commit.

City fees

Impact fees are the good news. An ADU with 750 square feet or less of interior livable space is exempt outright under Gov. Code § 66311.5(c)(1), and above that threshold impact fees must be charged in proportion to the size of the ADU relative to the house rather than at the full rate a new home would pay. A unit under 500 square feet is also outside school impact fees and does not increase assessable space (Gov. Code § 66311.5(c)(3)). MBMC § 10.74.070(A) still cross-references the old Gov. Code § 66324, which SB 543 renumbered to § 66311.5 effective 1 January 2026.

Building permit and plan check fees are separate, apply at any size, and are valuation-based rather than a flat ADU rate. Two local steps carry their own costs and are easy to miss: MBMC § 10.74.070(B) requires letters of service availability for water and sewer to go to the Building Official, and the Handout’s own disclaimer states that a Change of Address application and its associated fees are required as part of the ADU plan check process.

What it earns

Use a government benchmark rather than a listing site. For the Los Angeles–Long Beach–Glendale HUD Metro FMR Area, the FY 2026 Fair Market Rents as revised are $2,079 for a studio, $2,328 for a one-bedroom, $2,903 for a two-bedroom, $3,681 for a three-bedroom and $4,098 for a four-bedroom, published at 91 FR 21301 and effective 21 May 2026. Those figures cover the whole metro across all housing stock and ages, most of it older than anything you would build. A new, well-finished detached ADU typically rents above them, and a beach-adjacent Manhattan Beach address with the El Segundo employment corridor immediately north supports that. Run your own numbers on our ADU ROI calculator.

When an ADU isn’t the right move

A guide that never says “not you” is a brochure. Four situations where an ADU here is the wrong call, or the wrong call right now.

• Your plan depends on nightly rental income. The 30-day minimum is written into the recorded covenant and into state law, and it is not waivable. If short-term rental is the business case, there is no version of this that works in Manhattan Beach.
• You are counting on selling the unit separately. Manhattan Beach has not adopted an AB 1033 condominium opt-in, so an ADU here cannot be sold apart from the house. If your exit depends on that, you are planning around a policy change that may not come.
• You wanted a two-story detached unit in the open yard. The envelope at grade is about 20 feet. The 26-foot allowance requires the unit to sit directly above or below a detached garage, which is a different building and a different site plan.
• You need it finished in under six months. Design through move-in runs roughly six to nine months on a Signature plan and longer on a custom one. A family situation that needs housing sooner is better served another way.

The rules that make Manhattan Beach different

The Coastal Zone

Manhattan Beach has a certified Local Coastal Program, but it does not yet contain ADU provisions. Ord. 25-0004 added a new Chapter A.74 to the Local Coastal Program alongside amendments to Chapters A.12, A.16, A.84, A.94 and A.96, and the City states that it is still awaiting California Coastal Commission certification of those amendments. Until certification, the City’s published position is that ADUs and JADUs proposed in the Coastal Zone are subject only to applicable state law.

That has a real upside. The local development standards in MBMC § 10.74.050 — the 50 percent attached cap, the guest house rule, the deck and glazing rules — do not apply on a coastal lot. What applies is Gov. Code §§ 66314 to 66332 for ADUs and §§ 66333 to 66339 for junior ADUs, which is the same floor every city in California must meet. You still need a coastal development permit alongside the building permit, and the City’s own Interactive Map is the tool it points homeowners to for checking whether a specific parcel is inside the zone.

Two caveats belong with the good news. Gov. Code § 66329 does not alter or lessen the effect of Coastal Act resource protection policies, so habitat, public access, public view corridor and coastal hazard requirements still apply on their own terms. And the City states that inside the Coastal Zone the required on-site parking for the primary dwelling must be maintained at all times — the one place its published parking position differs from the rest of the city.

Parking, and the one place the local text is narrower

Table 3 of the City’s Handout is unambiguous outside the Coastal Zone: no additional or replacement parking is required. The ordinance text is drafted more tightly. MBMC § 10.74.050(E)(4) says that where a garage, carport, covered parking structure or uncovered space is demolished or converted for an ADU, those spaces need not be replaced if the project meets any of the criteria in Gov. Code § 66322(a). State law does not attach that condition.

Floor area, and the § 66323 carve-out

Manhattan Beach lots are small and buildable floor area is the binding constraint on most of them. An ADU built on the local ADU Permit track counts toward the maximum buildable floor area for the lot. An ADU built as a § 66323 unit does not: Table 3 of the Handout states that 66323 ADUs are not counted toward the maximum total buildable floor area applicable to the project site, and MBMC § 10.74.050(B)(2)(e) carries the same carve-out. That single line decides which pathway a lot of projects here should take.

The guest house rule

This one is specific to Manhattan Beach and it catches Hill Section properties in particular. MBMC § 10.74.050(C) provides that where an ADU is proposed on a lot that already has a guest house, either the guest house or the ADU — but not both — must be attached to the primary dwelling, unless the project complies with all the requirements of Gov. Code § 66323(a). A guest house, or accessory living quarters as MBMC § 10.04.030 defines it, is not an ADU and never has been. If you have one, the § 66323 pathway is worth looking at first.

Design rules that shape the drawing

• Decks. No outdoor deck may sit more than 30 inches above local grade inside the primary dwelling’s required yards. Landings sized for required ingress and egress are excepted.
• Alley access. Where the lot abuts an alley, any new driveway access for the ADU must come off the alley.
• Second-story glazing. On a non-alley lot, exterior openings within 12 feet of a rear line or 10 feet of an interior side line need translucent glazing, either inoperable or set at least 5 feet above the finished floor.
• Kitchen, foundation and access. Every ADU needs at least one permanently installed stovetop appliance, a permanent foundation and a separate exterior entrance.

All four sit in MBMC § 10.74.050(D) and all four apply on the ADU Permit track. None of them applies to a § 66323 unit, and none of them applies in the Coastal Zone while the Local Coastal Program amendment is uncertified.