The anatomy of an LA ADU build, line by line

An all-in number is useful only when the scope behind it is visible. Organize an ADU budget across soft costs, site work, construction, and contingency, then label each line as known, an allowance, excluded, or unresolved. What moves each category is the property's access and slope, existing panel and utility capacity, sewer lateral condition, foundation type, design, systems, and finish scope—not a market average. Get a written, itemized proposal before you sign, and stress-test it against the cost breakdown and the ROI calculator.

Soft costs

Soft costs cover everything you pay before a single nail is driven: architectural design, structural and Title 24 engineering, soils reports on hillside lots, surveys, plan check fees, school district fees, and utility connection fees. The scope and complexity of your design, your lot's slope and soils, and your city's specific fee schedule set the total — check your city's current planning and building fee schedule directly for the fee line items. The Title 24 guide walks the energy-code half in detail.

• —Architectural design — scales with unit customization, number of revisions, and whether the plan is stock or fully custom.
• —Structural + MEP engineering — driven by foundation type, structural complexity, and coordination with existing systems.
• —City plan check + permit fees — set entirely by your city's own current fee schedule; confirm the exact figure on your city's planning or building department fee page before budgeting.
• —School-facility fees — Government Code § 66311.5(c)(3) gives a specific assessable-space rule for ADUs and JADUs under 500 sq ft; confirm the current school-district determination for the actual scope. This is separate from the statute's 750 sq ft impact-fee rule.
• —Geotech report on hillside lots — needed whenever slope or soil conditions require it, and priced by scope of investigation — see the hillside soils guide.

Site work

Site work is the silent budget killer. Demolition, grading, sewer lateral verification, panel upgrades, and trenching for new utility runs all live here. A flat lot with a recently upgraded panel and a short utility run costs far less to prep than a hillside lot with an aging, undersized panel and a long sewer run. Have your contractor inspect the panel amperage, sewer lateral, and grading needs on-site before assuming a number. The utility connection map explains which workflows drive which line items.

Hard construction

Construction may include foundation, framing, enclosure, mechanical, plumbing, electrical, interiors, fixtures, equipment, appliances, exterior work, and restoration. Owner and design decisions can move many of these lines materially: structural spans, window and door systems, envelope assemblies, mechanical strategy, cabinetry, fixtures, equipment, and finishes all affect scope. The drawings, specifications, allowances, and exclusions should make those decisions visible.

Where finishes actually move the number

1. 01Cabinetry — flat-pack to semi-custom is the widest swing in the finish package on an 800 sq ft unit.
2. 02Countertops — laminate to quartz is a moderate but noticeable swing.
3. 03Flooring — luxury vinyl to engineered hardwood adds a meaningful premium.
4. 04Bath fixtures — builder-grade to design-grade adds a mid-range premium.
5. 05Appliances — base package to a premium brand package adds a substantial premium.

Contingency

Any builder telling you a project doesn't need a contingency is selling you the lowest number, not the most accurate one. New flat-lot construction generally warrants a smaller cushion than conversions and hillside builds, because the discoveries (active termite damage, undocumented additions, failed foundations) almost always come from the existing structure. Ask any bidder to state their contingency percentage and what it's based on for your specific lot.

Where homeowners get surprised most

• —Sewer lateral capacity verification — an aging or undersized lateral can trigger a full replacement; have it scoped before you budget.
• —Panel upgrade — required whenever the existing panel's capacity can't support the new unit's load; confirm existing amperage with an electrician.
• —Title 24 — heat pump, induction range, and Energy Star window requirements add cost versus older code; see the Title 24 guide for what's mandatory.
• —Landscape restoration — most quotes don't include planting or hardscape repair after trenching.

Once proposals arrive, the proposal comparison in Project Studio maps them onto these cost buckets and keeps unstated items as unresolved rather than zero.