ADU type
Garage Conversion ADU
A garage conversion turns an existing detached or attached garage into a permitted ADU. It's the fastest path to a rentable unit because the shell already exists — but the existing foundation, slab elevation, and lack of insulation decide whether it's actually cheap.
What it is
- Conversion of an existing garage (detached or attached) into a permitted dwelling unit.
- Statewide ADU law guarantees approval — local rules can't require you to replace the lost parking.
- Typically 350–600 sqft (standard 2-car garage footprint).
- Existing slab is often raised, sloped, or thin — most projects pour over or replace the slab.
- Title 24 requires full insulation, energy-compliant windows, and a heat pump or mini-split — the shell is rarely the cheap part.
Los Angeles · 2026
$185K – $310K all-in
$320 – $500/sqft
Slab work, Title 24 envelope, and panel upgrades are the three biggest cost drivers.
Bay Area · 2026
$240K – $410K all-in
$420 – $620/sqft
PG&E service upgrade and SFPUC sewer lateral compliance commonly add $20K–$45K.
When it fits
- Garage is structurally sound (no termite damage, no sinking slab).
- You want the fastest legal rental — 5–8 months door-to-door is realistic.
- Budget is tight: $180K–$320K range is achievable.
- You don't need a 1,200-sqft unit — converting and adding sqft loses the speed advantage.
When it doesn't
- Garage is set forward of the house line — many cities still apply primary-house setbacks to ADUs in the front yard.
- The garage is built into a hillside or has a low ceiling (<7 ft) — code clearances will force a teardown.
- You need 2+ bedrooms — typical garage footprint maxes out at 1 bedroom + den.
Permit pathway
Los Angeles
Fastest ministerial path. LADBS often issues in 30–45 days. No setback enforcement on the converted footprint — state law overrides local setback rules for existing garages.
Bay Area
Same ministerial path, but San Francisco and Berkeley require a soft-story compliance check if the garage is under living space.
Realistic timeline
Design + permit: 8–12 weeks. Construction: 12–20 weeks. Plan on 5–8 months from contract signing.
FAQ
- Do I have to replace the parking I lose?
- No. California law (Gov. Code §65852.2(e)) explicitly waives parking replacement when you convert a garage to an ADU. Cities cannot require you to add a new parking space.
- Can I keep the existing garage door and just frame inside it?
- No — Title 24 envelope requirements and egress rules require a real, insulated wall in place of the garage door. Many designers preserve the look with a wall that mimics the door panels.
- Will I have to dig up and replace the garage slab?
- Usually pour over it, not replace. Most existing garage slabs are 3.5" thick with no vapor barrier — we add a vapor barrier and a 2" overpour to meet code and avoid moisture issues.
- Can I expand the garage at the same time?
- Yes, but it changes the math: expansion is treated as new ADU construction (full setbacks, height limits). The expanded portion costs detached-ADU money, not conversion money.