Manhattan Beach ADU Construction — Sand Section Compliant, Coastal-Permitted, Marine-Built
The three things that make a Manhattan Beach ADU harder than a Valley ADU
One: lot size. Manhattan Beach lots are typically 30 by 90 or 40 by 90 — small. Setback math is tighter, lot coverage caps bite earlier, and a 1,200 sq ft ADU usually requires going up rather than out, which triggers the Sand Section Ordinance height analysis. Two: the Coastal Zone. Anything west of Highland Ave, anything within 300 feet of the public beach, anything visible from a public viewing area — Coastal Development Permit required. CDP adds three to six months to your permit timeline. Three: salt air. Every fastener, every window, every exterior finish has to spec out for the marine environment or you will see corrosion bleed within two years. Our 2026 cost band: $280K to $560K depending on size, story count, and CDP trigger.
Cost band breakdown
$280K to $360K covers a detached 600-750 sq ft single-story rear-yard ADU on a Sand Section lot without CDP trigger, marine-grade exterior, full kitchen and bath, separate utility meter. $390K to $480K is a 900-1,100 sq ft two-story ADU with view-axis windows, full marine envelope, and a CDP-required design review. $510K to $560K is a 1,200 sq ft maximum-build ADU with a CDP, ocean-view roof deck, and a high-end interior package. State law caps ADU square footage at 1,200 sq ft; we do not build over that. Three line-item quote: shell, MEP, finishes.
AB 1033, SB 9, and the Coastal Commission
California AB 1033 lets cities allow ADUs to be sold separately as condos — Manhattan Beach has not opted in as of 2026, so you cannot sell the ADU separately. SB 9 lot splits and duplex conversions are restricted in MB's single-family zones due to local interpretation. The state ADU law (Government Code 65852.2) still mandates that the city approve a permitted ADU on most single-family lots within 60 days of complete submittal — but the Coastal Zone overlay legally extends that timeline. We file with both the city and the Coastal Commission in parallel where required. Total permit timeline: 4-6 months without CDP, 8-14 months with CDP.
Build timeline week by week
Months 1-4 (no CDP) or months 1-8 (with CDP): plans, structural engineering, Title 24 energy modeling, geotechnical if hillside, permit submittal, plan-check corrections, permit issuance. Month 1 of construction: site protection, demo if applicable, foundation excavation, foundation pour. Month 2: framing, sheathing, roof structure. Month 3: roofing, windows, exterior dry-in. Month 4: rough MEP, city rough inspections. Month 5: insulation, drywall, interior trim start. Month 6: kitchen and bath finish, flooring, paint. Total construction: 5-7 months for single-story, 7-10 for two-story. Permit + construction = 6-14 months end to end.
What the first walk-through gets you
One site visit, 60 to 90 minutes. You leave with (1) feasibility read — does your lot legally support the ADU you want, given setbacks, lot coverage, and Sand Section height, (2) a 2026 cost band on real Manhattan Beach ADU invoices, (3) CDP risk read — is your project triggering Coastal Commission review and what does that add to schedule, (4) two comparable builds we have delivered. No commit. If we tell you the lot will not support what you want, we tell you on the first walk, not after you have paid for plans. That conversation is free.
FAQ
Can I build an ADU in the Sand Section?
Usually yes, but the Sand Section Ordinance height limits (26 ft sloped roof, 22 ft flat) typically force a single-story or a tight two-story design on small lots. We do the feasibility math on the first walk.
What triggers a Coastal Development Permit?
Lot west of Highland Ave, within 300 ft of the mean high tide line, or in the appealable zone. Manhattan Beach Planning confirms CDP trigger at intake. We file the CDP application in parallel with the city permit; the Coastal Commission and the city run separately.
Can I rent the ADU short-term (Airbnb)?
Manhattan Beach prohibits short-term rentals (under 30 days) in residential zones. You can rent the ADU long-term (30+ days) without restriction.
Do I need a separate utility meter?
Not required by state law, but recommended for rental separation and resale clarity. Add $8K-$15K for SCE separate service and a separate gas meter through SoCalGas. We coordinate both.
What about the existing house — does the ADU change my property taxes?
The ADU adds assessed value (Prop 13 base year reset on the new improvement only, not the existing house). Typical tax increase: $3,500-$8,500/year on a $400K ADU. Your CPA confirms the exact number.
Can the ADU be detached or attached?
Both legal. Detached is cleaner for rental separation. Attached (garage conversion or addition) often clears plan check faster because the building footprint already exists. We design both.
What is your warranty?
Two years workmanship, ten years structural per California statute, manufacturer warranties on all installed equipment. CSLB-licensed GC since 2023, architectural design firm since 2016, 200+ LA County projects including coastal builds.