If you are adding an accessory dwelling unit in Orange County, there is a good chance the first thing that has to go is the detached garage. It is usually the only structure on the lot with enough footprint to matter, and it is almost always in the right place: at the back, off the driveway or the alley, away from the house.
What surprises most homeowners is that the demolition is rarely the hard part. A single-car garage comes down in a day. The weeks that disappear from an ADU schedule go to paperwork, utility sign-offs, and decisions about the slab that nobody made early enough. Here is the sequence that actually works, and where projects lose time.
The demolition permit and the ADU permit are one application now
This is the single most useful thing to know, and plenty of homeowners are still being told otherwise. Under state ADU law, a local agency has to review and issue the demolition permit for a detached garage that is being replaced with an ADU at the same time as the ADU permit itself (Government Code section 66314(e)). You should not be sent away to pull a separate demolition permit first and come back.
The same section removes another old delay. The city cannot require written notice to neighbors or a placard posted on the property for the demolition of a detached garage, unless the property sits in an architecturally and historically significant district (section 66314(f)). In most of Orange County it does not. In Old Towne Orange and parts of Old Town Tustin it might, and that changes the timeline.
One housekeeping note: California's ADU statutes were renumbered as of January 2025 and now live at Government Code sections 66310 through 66342. If your plan checker or your contractor is still citing section 65852.2, the substance is largely the same but their section numbers are out of date.
Decide whether you are converting or demolishing before anything else
A detached garage can become an ADU two ways: convert the existing structure, or tear it down and build new. These are different projects with different rules, and the choice drives everything downstream.
Conversion keeps the existing walls and foundation. It is cheaper on paper and it sidesteps setback questions entirely. But you inherit whatever is there: a 1950s slab with no real footings, walls with no insulation and no shear capacity, a roof framed to keep rain off a car rather than to carry a conditioned living space. On a lot of older Orange County garages, the cost of bringing that shell up to habitable standard lands within a few thousand dollars of new construction, and you end up with the worse building.
Demolition and rebuild costs more up front and buys you a structure designed for the job: real footings, current insulation and energy compliance, the ceiling height you want, and a layout that is not dictated by where the garage door used to be.
The honest test is the foundation and the framing. If a structural engineer tells you the slab has to come out anyway, the conversion argument has already lost, because at that point you are demolishing the expensive part and keeping only the walls.
You do not owe the city replacement parking
This one still gets argued at the counter. When off-street parking is demolished or converted in conjunction with building an ADU, the local agency cannot require those spaces for the primary house to be replaced (section 66314(d)(11)). Uncovered spaces you remove do not have to be replaced either.
So losing the two-car garage does not obligate you to build a carport or pave a pad somewhere else on the lot. If you are told otherwise, that code section is worth quoting.
Keep the footprint if the old garage sits close to the line
Here is the rule that quietly saves projects. A new ADU normally has to hold four-foot side and rear setbacks. Plenty of older Orange County garages sit at one foot, or right on the property line, which would appear to make a same-size replacement impossible.
State law carves this out. No setback is required for an ADU created in a new structure built in the same location and to the same dimensions as an existing structure (section 66314(d)(7)). Tear the garage down and rebuild in exactly its footprint, and you keep its setbacks.
The catch is in those words, same location and same dimensions. Push the walls out a foot to gain a little floor area and you have left the exemption behind and bought yourself a four-foot setback on every side, which usually costs more space than the foot you gained. Have your designer test both versions before demolition, because once the garage is gone the evidence of its footprint goes with it. Photograph it, dimension it, and keep the survey.
The asbestos survey comes before the permit, not before the machine
SCAQMD Rule 1403 governs demolition across the South Coast air basin, and it applies to a detached garage the same as it applies to a house. You need a survey by a certified asbestos consultant before demolition, and notification to SCAQMD with ten working days of advance notice, whether or not the survey finds anything.
Ten working days is two calendar weeks. Homeowners who treat the survey as something to arrange once the permit is in hand lose those two weeks at the worst possible moment, with the builder already scheduled and the crew booked. Book the survey while the plans are still in plan check.
Old garages are a realistic place to find asbestos: transite roof and wall panels, older roofing felt, sheet flooring if the space was ever finished, and joint compound. Finding it is not a crisis and it is not necessarily expensive. Not knowing about it until the crew arrives is both.
Lead is a crew question more than a schedule question
If the garage was built before 1978 there is a fair chance of lead paint, particularly on doors, trim and any painted siding. Cal/OSHA's lead in construction standard applies to work that disturbs it, so this mostly affects how the demolition contractor sets up, protects and monitors the site rather than how long the job takes. It is worth confirming your contractor has priced it in rather than discovering it as a change order.
Utility disconnects are what actually delay people
Of everything on this list, this is where Orange County ADU projects most reliably lose a month. Most cities will not issue the demolition permit until they have written confirmation that the services to the structure have been disconnected and capped.
That can mean Southern California Edison for the electrical feed, SoCalGas if anything was ever piped out there, and your water district, whether that is Moulton Niguel, Santa Margarita, IRWD, the City of Orange or another. Each has its own request process and its own queue, and none of them move faster because your builder is waiting.
Two things help. Start the disconnect requests the same week you submit the ADU application, not when the permit is issued. And check what is actually running out to the garage before you assume: a subpanel fed from the house, a hose bib, an old gas line to a dryer or a heater, sometimes a sewer connection if there was ever a sink or a half bath. A buried line nobody knew about is a bad discovery mid-demolition.
If the ADU is going back in the same place, ask your builder which of those services are worth preserving and reusing rather than killing and re-running. Sometimes the sewer lateral and the water stub are the most valuable things on the site.
The slab is a decision, not a default
Most garage slabs in Orange County are three and a half to four inches of unreinforced concrete poured on grade, with a thickened edge if you are lucky. They were built to park a car on, not to carry a dwelling with a code-compliant footing, a shear wall schedule and a hold-down at every corner.
So in most cases the slab comes out with the structure, and your ADU gets an engineered foundation designed to a soils report. Removing it at the same time as the building is far cheaper than bringing equipment back for it later, which is exactly why the decision has to be made before the demolition is quoted rather than after.
Occasionally an engineer will approve reusing a slab, usually a newer one, sometimes with an overlay or a perimeter underpin. That is their call and it needs to be on paper before demolition day, because deciding when we see it turns into a second mobilization.
What your builder actually needs from the demolition
Handing a builder a cleared lot is not quite the same as handing them a lot they can start on. Worth agreeing in writing before the work begins: whether the slab and footings are going, how deep the site is cleared and whether excavations are backfilled and compacted or left open for the new foundation, where the existing utilities are terminated and flagged, whether hardscape and the old driveway approach are in scope, and who deals with the fence and the gate if equipment has to come through them.
Get the debris diversion paperwork too. Most Orange County cities require a construction and demolition recycling report as a condition of the permit, and it is far easier to collect the weight tickets as the job runs than to reconstruct them from memory afterwards.
A sequence that holds up
Roughly in the order that works: have a designer and a structural engineer settle convert versus rebuild and, if you are rebuilding, pin the footprint to the existing garage. Submit the ADU application with the demolition included in it. Book the asbestos survey immediately and file the SCAQMD notification. Start the utility disconnect requests that same week. Order the soils report if the foundation design needs one. Then, once the permit is issued and the disconnects are confirmed in writing, demolish, remove the slab and clear the site in a single mobilization.
On the clock: the agency has to approve or deny a complete ADU application within 60 days (sections 66317(a) and 66320(a)), and a 2025 amendment requires the agency to tell you within 15 days whether the application is even complete. Both of those run on a complete application, which is precisely why the survey, the disconnects and the engineering want to be moving in parallel rather than one after another.
Where the money goes sideways
The three expensive surprises, in rough order of how often they turn up: a second mobilization because the slab decision got deferred; two weeks of dead time waiting on a Rule 1403 notification that could have been filed a month earlier; and a footprint that grew by a foot in design and quietly gave up a setback exemption the old garage had held for sixty years.
None of those are demolition problems. They are sequencing problems, and all three are avoidable on a whiteboard before anyone starts a machine.
Clear Path Demolition removes detached garages, sheds and outbuildings for ADU projects across Orange County, and we are used to working to a builder's schedule and a plan checker's conditions rather than our own. If you want the demolition scoped properly before your ADU goes into plan check, call (949) 603-3366 or request a free quote and we will walk the property with you.
