Plan, cost, and build your ADU
with the receipts
in hand.
The complete 2026 guide to the ADU construction process — plus a free cost calculator, financing options, vetted local builders, and tools that pencil out your project before you call anyone.
No spam. Independent guidance. We may earn a referral fee when you connect with a builder — it never changes our editorial.
$284k–$382k
Mid-finish detached ADU, moderate site complexity.
- Design + permits
- 11%$36k
- Shell + framing
- 28%$91k
- MEP
- 16%$52k
- Finishes + utilities
- 29%$94k
- Sitework + soft
- 16%$52k
Architect, structural, city fees
Foundation, walls, roof
Electrical, plumbing, HVAC
Cabinets, floors, fixtures
Drainage, landscaping, contingency
The tools
Plan your project before you call a builder.
Each tool runs in your browser, takes under five minutes, and emails the results so you have them when you're ready.
ADU cost calculator
Low/mid/high estimate by state, type, size, and finish level.
Estimate costROI calculator
Cash flow, payback period, and property-value uplift.
See the mathLoan calculator
HELOC, cash-out refi, construction and renovation loans compared.
Compare loansFeasibility check
Seven questions to find out if you can actually build on your lot.
Check feasibilityThe ADU process
Six phases, from idea to occupancy.
Most homeowners spend 9–18 months from first sketch to move-in. Here's what happens and when.
- 012–6 wks
Planning
Test feasibility, set budget, pick a path.
Phase guide - 024–10 wks
Design
Floor plan, elevations, site layout.
Phase guide - 036–16 wks
Permits
Submittal, plan check, revisions.
Phase guide - 044–8 wks
Financing
HELOC, refi, or construction loan close.
Phase guide - 0516–28 wks
Construction
Foundation through final finishes.
Phase guide - 062–4 wks
Inspection
Final, occupancy permit, move-in.
Phase guide
● Typical timeline · 9–18 months end-to-end
See the complete process guideFeatured guides
Start with the questions everyone asks.
PRICE
How much does an ADU cost in 2026?
Breakdowns by state, ADU type, and finish level — with the line items that move the most money.
Read the guideBUILD
Garage conversion ADU guide
The fastest, cheapest path to an ADU — if your garage qualifies. Costs, permits, and pitfalls.
Read the guideCOMPARE
ADU vs. room addition
When an ADU outperforms a traditional addition — and the cases where it doesn't.
Read the guideFor buyers
Looking for a home that
already has an ADU?
We track active listings with permitted ADUs in California and expansion markets — plus the buying-guide essentials (financing, valuation, rent-ability) you need before you make an offer.
FAQ
The questions every ADU homeowner asks first.
Short, sourced answers to what costs, what takes how long, and what the permit and value math actually looks like in 2026.
- What is an ADU?
- An ADU — Accessory Dwelling Unit — is a self-contained second home on a single-family lot, with its own kitchen, bathroom, and entrance. ADUs come in four common forms: detached (a separate small building), attached (added to the main home), garage conversion (built into an existing garage), and junior ADU or JADU (carved out of existing living space, capped at 500 sq ft).
- How much does an ADU cost in 2026?
- Total ADU cost in 2026 typically runs $100,000–$400,000+, depending on type, size, and location. Garage conversions average $80K–$175K, attached ADUs run $150K–$300K, and detached ADUs run $200K–$400K+. California is roughly 20–35% above the national average. Use our free ADU cost calculator for a state- and finish-level-specific estimate in under 90 seconds.
- How long does it take to build an ADU?
- Plan for 10–18 months from your first serious conversation to a certificate of occupancy. Design takes 2–5 months, permitting takes 3–9 months, and construction takes 6–10 months. Garage conversions and pre-approved city plans can compress that significantly — San Jose currently runs the fastest California permit cycle at 35–55 days.
- Will an ADU add value to my home?
- Yes. A permitted ADU typically adds 50–70% of build cost to appraised property value in the short term and 80–100% once rental income is documented. Fannie Mae and Freddie Mac now formally allow lenders to count projected ADU rental income toward loan qualification, which is why ADU-aware lenders can underwrite higher loan-to-value ratios than they did a few years ago.
- Do I need permits to build an ADU?
- Yes — every habitable ADU requires a building permit, and most jurisdictions also require planning approval, mechanical/electrical/plumbing permits, and a final certificate of occupancy. California state law (AB 881, SB 543) caps permit review timelines and limits what cities can require, but you still need a full permit set. Total California permit costs range from about $12,000 to $77,000 depending on city, size, and utility connection needs.
The free download
Get the 2026 ADU
Homeowner's Playbook.
A 27-page PDF covering process, costs, permits, financing, and the five most common ways homeowners overspend on an ADU. Plus monthly updates on what's changing in state ADU law.