ADU and Garage Conversion Costs and Timeline (2026)
What an accessory dwelling unit or garage conversion really costs in 2026, broken down by type, plus the rules and timeline most homeowners don't see coming.
Conversion vs. detached ADU
Converting an existing attached garage into a livable unit costs $60,000–$150,000 because the structure, foundation, and roof are already there. The big costs are insulation, plumbing, HVAC, egress windows, and meeting energy code.
A detached ADU — a freestanding small dwelling on the same lot — runs $200,000–$450,000 depending on size (400–1,200 sq ft is typical), site work, utility runs, and finish level. It's essentially building a small house.
Permits, zoning, and utilities
Most jurisdictions now allow ADUs by right, but every one has its own setback, height, parking, and owner-occupancy rules. Confirm your local rules before designing — they shape the whole project.
Utility hookups (sewer tap, water meter, electrical service upgrade) often run $15,000–$40,000 and are routinely missed in early budgets.
Return on investment
A long-term rental ADU typically grosses $1,500–$3,500/month depending on location and size, paying back the build in 6–10 years. Resale value increases are usually 1.5–2x the build cost in high-demand markets.
Frequently Asked Questions
- How long does a garage conversion take?
- Typically 3–5 months: 4–6 weeks for design and permits, 8–14 weeks of construction.
- Can I build an ADU in my backyard?
- In most US states with statewide ADU laws (CA, OR, WA, UT, etc.) — yes, subject to local setback and height rules. Other states leave it to municipalities. Always confirm with your city or county planning office.
- Does an ADU add value to my home?
- Yes — both as rental income and at resale. Appraisers typically value a permitted ADU at the cost of construction or higher in tight rental markets.