What ADU Construction Involves
An accessory dwelling unit is a complete, independent home built on a lot that already has one. It has its own kitchen, its own bathroom, its own entrance, and its own utility connections, which is what separates it from a room addition or a converted bonus room. Building one is closer to building a small house than to remodeling an existing one, and that distinction drives almost everything about cost, timeline, and who is qualified to do the work.
California has spent the better part of a decade removing the obstacles. A series of state bills starting in 2017 stripped away the local rules that used to make ADUs impractical: minimum lot sizes, floor area ratios, and open space requirements can no longer be used to block a unit of at least 800 square feet, parking replacement is no longer required when an ADU takes over a garage, and homeowners associations can no longer prohibit an ADU on a single-family property. According to the City of Los Angeles ADU program, permits for ADUs and junior ADUs must now be approved or denied within 60 days, down from the 120 days allowed under previous law.
What state law did not change is the building itself. An ADU still needs a foundation, a code compliant structure, its own electrical service, water and sewer connections, and a Title 24 energy compliance path. That is general contractor work, and it is the half of the project where most of the money and all of the risk actually sits.
ADU Types We Build
Detached ADU
A standalone structure, usually placed in the rear yard, with no shared walls. This is the most flexible option and the one that produces the most usable, private living space. It is also the most involved build, because everything starts from bare ground: excavation, foundation, full framing, roofing, and new utility runs from the main house or the street.
Attached ADU
A new unit that shares at least one wall with the existing home. It reuses part of the existing structure and can sometimes tie into existing utilities, which shortens the build, but it requires careful structural work at the connection point and a clean separation of the two dwellings for code purposes.
Garage Conversion
An existing garage converted into a dwelling. The foundation, walls, and roof already exist, which makes this the fastest route to a finished unit. The work is in what is not there yet: insulation, a code compliant floor assembly, egress windows, ceiling height, plumbing runs, a new electrical subpanel, and often a new roof if the existing one has reached the end of its life. A garage conversion also frequently needs the slab evaluated before anything else is decided, because a slab poured for a car is not always adequate for a dwelling.
Garage Addition
A new unit built above or alongside an existing garage, sharing at least one wall with it. Building above a garage almost always requires structural reinforcement of the existing structure, which is a foundation and framing question before it is a design question.
Junior ADU (JADU)
A unit of no more than 500 square feet created within the walls of the existing home or an attached accessory structure. A JADU may share a bathroom with the main house and only has to meet efficiency kitchen requirements, which makes it the smallest and simplest category. California allows one ADU and one JADU on the same residential property.
Signs an ADU Is the Right Project for Your Property
Homeowners usually arrive at an ADU through one of a few situations, and recognizing which one you are in helps set the scope before anyone talks about design.
- You need housing for family, not a rental. Aging parents or adult children who need independence and proximity at the same time. This usually points toward a detached unit with real separation, or a JADU if the need is modest and the budget is tight.
- You want rental income from land you already own. The property is already yours, and adding a unit costs less than buying one. This is the most common motivation and the one most sensitive to build cost, which makes an accurate written estimate up front more important than a low headline number.
- You have an unused or underused garage. A detached garage nobody parks in is the single cheapest starting point for a dwelling, because the shell already exists.
- You have rear yard depth and utility access. Rear yard space is only useful if crews and materials can reach it. A wide side yard or alley access changes what a detached unit costs.
- You are already planning a major remodel. Combining an ADU with other work can consolidate permits and trade mobilizations that would otherwise happen twice.
Comparing the ADU Types
| Detached | Attached | Garage Conversion | Junior ADU | |
|---|---|---|---|---|
| Existing structure reused | None | One or more walls | Slab, walls, roof | Interior of the home |
| Typical build complexity | Highest | High | Moderate | Lowest |
| Utility work | Full new runs | Often extends existing | New subpanel, new plumbing runs | Usually ties into the home |
| Privacy and separation | Highest | Moderate | High | Lowest |
| Size ceiling | Largest | Large | Limited by the existing footprint | 500 sq ft |
| Best suited to | Long-term rental or full independent living | Lots without rear yard access | An unused garage on a usable slab | Family use on a limited budget |
What Drives ADU Cost
ADU pricing varies more than any other project we quote, and the variation is not arbitrary. These are the factors that actually set the number:
- Type and size. A 500 square foot junior ADU inside existing walls and a 1,000 square foot detached unit built from bare ground are different projects, not different sizes of the same project.
- Site access. If a concrete truck, lumber delivery, and excavation equipment can reach the rear yard, the job runs on schedule. If everything has to be carried through a side gate, labor climbs on every phase.
- Foundation and soil. Detached units need a new foundation, and sloped lots, expansive soils, or a required soils report change that scope significantly.
- Utility connections. Water, sewer, gas, and electrical have to reach the new unit. Whether your existing main panel has the capacity for a second dwelling, or needs an upgrade, is one of the largest single swing items on an ADU quote.
- Slab condition on a garage conversion. An existing slab has to be evaluated for thickness, reinforcement, and moisture before it can carry a dwelling. Sometimes it works as is, and sometimes it comes out.
- Finish level. Fixtures, cabinetry, flooring, and appliances span a wide range, and this is the part of the budget you control most directly.
- Permit and plan-check scope. Engineering, Title 24 documentation, and any corrections required during plan check are real line items and belong on the quote in writing.
We do not publish a headline ADU price, because a number that ignores your lot, your slab, and your panel capacity is not useful to you. What we do instead is walk the property, identify which of the drivers above apply, and give you an itemized written estimate before any work is scheduled.
The Disadvantages Nobody Puts on Their Website
An ADU is not right for every property, and you should hear that before you spend money on plans.
Rear yard space is permanent once it is built on. If your yard is the reason you bought the house, a detached unit will change how the property feels in a way that plans and renderings do not convey. Construction on an occupied property is disruptive for months, not weeks, and a detached build means heavy equipment and open trenches in your yard for part of that time. If your main electrical panel is undersized, the upgrade is not optional and it is not cheap. Sloped and hillside lots add engineering that flat lots do not need. And if your primary goal is rental income on a short timeline, the permitting and construction schedule for a detached unit is long enough that it needs to be part of the decision rather than a surprise at the end of it.
None of these make an ADU a bad idea. They make it a project that should be scoped accurately at the start, which is what a site visit is for.
Permits and California Requirements for ADU Construction
An ADU is a permitted, inspected build with no exceptions. In the City of Los Angeles the permit runs through the Los Angeles Department of Building and Safety, and surrounding jurisdictions run their own building departments with their own submittal requirements. Under current state law the building department must approve or deny an ADU or JADU application within 60 days of a complete submittal.
Expect a building permit for the structure, with electrical, plumbing, and mechanical permits either included or pulled separately depending on the jurisdiction. Structural plans typically require engineering, and every ADU has to meet Title 24 energy requirements, which govern insulation, windows, water heating, and HVAC efficiency. Fire separation and egress requirements apply to any converted space, which is why a garage conversion needs proper egress windows and ceiling height rather than just new drywall. State law also limits impact fees on ADUs under 750 square feet and requires that any fees be proportional to the size of the primary residence.
A contractor who suggests building without a permit is offering you an unpermitted structure that will surface during any future sale, refinance, or insurance claim.
The Trades an ADU Actually Requires
An ADU touches nearly every trade we work in, which is why we build them under one contract rather than coordinating around other people’s schedules. A detached unit needs a new roof system, which is the same roof installation work we perform on new construction. The exterior needs a complete weather barrier and finish, the same assembly used in stucco installation on any new structure. New openings need framing and properly flashed window installation, and a compact unit is often the right candidate for an electric tankless water heater rather than a conventional tank. If your project is closer to expanding the existing house than adding a separate one, a room addition may be the better fit.
Financing
$0 down financing is available on ADU construction, and we will review the options with you during the free on-site estimate so the payment structure is settled before the project is scheduled.
ADU Construction Across Southern California
Wise Choice Remodeling builds ADUs throughout the five-county service area. Homeowners in Burbank, Glendale, and Pasadena are working with deep lots and older detached garages that convert well, while newer tract properties in Anaheim, Irvine, and Rancho Cucamonga more often suit a detached unit built from the ground up. Each city runs its own building department with its own submittal process, and we file and track the permit wherever your property sits.
Why Choose Wise Choice Remodeling for ADU Construction
We build what we plan
Design, engineering, permitting, and construction sit under one contract, not a referral to a builder you have not met.
15+ years of combined experience across every ADU trade
We have built foundation, framing, roofing, stucco, electrical, plumbing, HVAC, and finish work across Southern California, and an ADU needs all of them.
Licensed and insured general contractor
We pull the permit under our own license and carry the project through every inspection to final sign-off.
Your written estimate is your price
We itemize the estimate before work begins, and nothing gets added to the scope without your written approval.
2-year workmanship warranty
Our workmanship carries a two-year warranty on the structure we build, covering the trades we hold under the same contract.
Start With a Site Visit
An ADU is a serious investment, and the difference between one that pays off and one that becomes a problem is usually decided before a single permit is filed. Wise Choice Remodeling brings 15+ years of combined experience to ADU construction across Southern California, as a licensed and insured general contractor holding the full scope under one contract, one project manager, and one 2-year workmanship warranty. Call (818) 483-8055 or request a free written estimate, and we will walk your property, tell you plainly which ADU type fits it, and put a real number in writing.
