A garage gives you three genuinely different projects with very different risk profiles: convert it, build above it, or tear it down and replace it. This page compares all three, including the slab, framing and moisture problems that make conversion the least predictable of the three.
A standard 2-car garage conversion typically costs between $60,000 and $150,000, depending on structural needs and finishes.
Building an ADU above an existing garage is significantly more expensive, often rng from $150,000 to $350,000+.
The conversion process generally takes 8 to 12 months from initial design and permitting to final inspection.
California law allows homeowners to convert garages into ADUs without replacing the lost covered parking spaces.
Garage conversions must comply with energy codes, such as California's Title 24, which mandates specific insulation (e.g., R-15 for walls) and energy-efficient windows.
Figures below are researched market numbers for budgeting and comparison. They are not quotes. Final pricing depends on your site, your jurisdiction, finish selections, foundation and utility distance.
ADU rules are set locally and change often. These are the provisions that most commonly control the outcome. Verify against your own jurisdiction before you design anything.
A garage gives you three genuinely different projects and they have very different risk profiles. Converting the existing garage is the cheapest on paper and the least predictable in practice, because you inherit whatever the existing structure is. Building above the garage adds square footage without consuming yard. Demolishing and replacing with a purpose-built ADU costs the most and carries the fewest unknowns.
Conversion risk concentrates in three areas: the slab, the framing and the moisture history. Garage slabs are frequently thinner than a habitable-space slab, often unreinforced, and typically sloped to drain toward the door, which conflicts with a level finished floor. Garage framing may not be sized for the insulation depth or the loads a dwelling requires. And a garage that has taken water for twenty years may have sill and bottom-plate rot that nobody sees until the drywall comes off.
Building above requires that the existing structure and foundation can carry a new floor and roof load, which frequently means foundation work and new shear walls, and that is where above-garage budgets exceed expectations. Get a structural assessment before committing to that path. It costs little relative to the project and it is the only way to price the work honestly.
| Convert existing garage | Lowest apparent cost. Highest unknown-condition risk. |
| Slab condition | Often thin, unreinforced and sloped to drain. May need replacement. |
| Existing framing capacity | May not carry dwelling loads or insulation depth. |
| Moisture and rot history | Invisible until demolition. Budget a contingency. |
| Build above garage | Adds area without consuming yard. |
| Foundation and shear capacity | Frequently the controlling cost for building above. |
| Demolish and replace | Highest cost, fewest unknowns, best final product. |
| Parking replacement rules | Many jurisdictions no longer require it. Verify locally. |
Most pages on this subject put the cost behind a contact form. The reasoning is understandable and the result is that you cannot budget, cannot compare, and cannot tell whether a bid is reasonable until you have already given up your phone number to three companies.
We publish the figures instead. They are researched market ranges rather than quotes, and site conditions will move them more than any other factor, but a range you can plan against beats a call-back you have to wait for. The constraints that decide feasibility — setbacks, height, utility distance, site access — are stated up front for the same reason. If your project is not viable, that is worth knowing on the first visit rather than the third phone call.
Factory production windows move with queue depth, material lead times and seasonal demand. We quote the current window rather than a fixed promise, because anyone promising a specific delivery date months out without seeing the factory schedule is guessing. Permitting is usually the longer pole: in ministerial states the review clock is defined by statute, while in discretionary jurisdictions it can run considerably longer.
The sequence that controls your schedule is site plan, permit submittal, plan check and corrections, permit issuance, factory slot, delivery and set, then utility connection and final inspection. Factory build time overlaps permitting only if you commit to the slot before permits are issued, which carries its own risk.
Tell us the scope and the ZIP. You get a real delivered-and-installed number, not a "contact us for pricing" runaround.