2026 pricing guide
What an ADU actually costs in the Bay Area.
No allowances, no asterisks. Here's the real all-in number for designing, permitting, and building a modular ADU in the Bay Area in 2026, broken down by size, soft costs, and city.
All-in price by size (2026 Bay Area)
These are SHAPE's published starting prices for a typical lot across Mountain View, Palo Alto, Los Altos, Menlo Park, and the surrounding peninsula. They cover design, structural and MEP engineering, permits, factory build, transport, crane set, foundation, utility connections, and standard finishes.
- SHAPE Model 1, 400–500 sq ft, from $223,000 all-in.
- SHAPE Model 2, 500–750 sq ft, from $263,000 all-in.
- SHAPE Model 2X, 750–1,200 sq ft, from $343,000 all-in.
- Hillside and tight-access ADUs, typically $400k – $750k all-in.
Final fixed pricing depends on the lot, utility runs, finishes, and any exceptional site work. The published model prices cover a typical lot; hillside and tight-access work uses its own range.
What's actually in the number
A SHAPE quote is fixed and signed before construction starts. It includes:
- Architectural design, schematic through construction documents
- Structural, MEP, Title 24, and CalGreen engineering
- Full permit submittal and city corrections
- Factory fabrication of the modules
- Transport, crane set, and site assembly
- Foundation engineered to your soils
- Utility tie-ins on a typical lot
- Standard interior and exterior finishes
The only items quoted separately are exceptional site conditions, major grading, retaining walls, septic upgrades, long utility runs, and any finish upgrades you choose. Both are priced before you sign, not after.
Permit fees by city
City permit fees are paid to the jurisdiction and are not part of the construction quote. They generally run:
- Mountain View, typically $8,000 – $14,000
- Palo Alto, typically $12,000 – $20,000
- Los Altos, typically $10,000 – $16,000
- Menlo Park, typically $9,000 – $15,000
- Atherton / Hillsborough / Woodside, typically $15,000 – $25,000
California state law caps utility connection fees for ADUs under 750 sq ft at zero, a meaningful saving most homeowners aren't aware of.
How people pay for it
Because SHAPE builds permanent modular homes to California Building Code, ADUs qualify for standard financing:
- HELOC, most common. Tap existing home equity at prime-adjacent rates.
- Cash-out refinance, works well if your existing rate isn't already low.
- Construction-to-permanent loan, for homeowners without enough equity yet.
- Renofi / RenoFi-style loans, underwrite against post-build appraised value.
Bay Area ADUs typically appraise at $150 – $400 per added square foot and rent for $2,500 – $5,000/month, so most projects pay for themselves on a 7 – 12 year horizon.
Frequently asked
- What's the cheapest ADU I can actually build in the Bay Area?
- SHAPE Model 1 starts at $223,000 all-in for 400–500 sq ft on a typical lot. The final fixed quote depends on utilities, access, finishes, and site conditions. Hillside and tight-access projects use a separate $400,000–$750,000 range.
- Why is an ADU more expensive than a regular addition to my house?
- An ADU is a fully independent dwelling with its own kitchen, bathroom, HVAC, electrical panel, and utility connections. A typical addition shares those systems with the main house, so it's cheaper per square foot, but it doesn't rent, doesn't appraise as a separate unit, and doesn't add the same long-term value.
- Are there hidden costs I should plan for?
- Three things SHAPE flags upfront if relevant: (1) exceptional site work like retaining walls or major grading, (2) PG&E service upgrades if your panel is already maxed out, and (3) sewer lateral upgrades if yours is old or undersized. We assess these on the site walk before quoting.
- How long does it take to break even on an ADU as a rental?
- At $2,500 – $5,000/month gross rent, payback depends on the selected SHAPE model, the fixed quote for the lot, financing, vacancy, taxes, insurance, and maintenance. Many Bay Area projects target an 8 to 12 year cash-flow break-even horizon.
- Will SHAPE quote my project before I commit?
- Yes. We do a free 30-minute call to scope feasibility, then a paid feasibility study that produces a real fixed quote. You only commit to construction after you've seen the number.
Let's build it.
A free 30-minute call with our team. You'll leave with a feasibility read on your lot and a real sense of what the project costs and how long it takes.
