California law opened the door wider than ever for accessory dwelling units. Check whether your lot qualifies, see your rental income and payback period, then get permit-ready plans — all before you spend a dollar.
Setbacks, lot coverage, utilities, fire access, and local overlays all stack on top of state law. Most homeowners give up here, before anyone quotes them anything.
Everyone quotes build cost. Almost nobody shows you rent, cash flow, and payback — the only figures that tell you whether it's actually worth doing.
Feasibility, design, permits, utilities, build. Without milestones, the whole thing looks like one long undefined risk — so it stays a someday project.
Six questions. You get a feasibility verdict, a cost range, projected rent, monthly cash flow, and your payback period.
Feasibility, cost, rent, and payback
BestHouse is a California-licensed civil engineering firm and our design, drafting, and inspection services are only available for California properties. We can't process a request outside California at this time.
Pick a time below and we'll walk through your result together. Takes 15 minutes.
The right path depends on your lot, your budget, and what you're actually trying to accomplish.
DetachedA freestanding backyard unit with its own entry and utilities. Highest cost, highest rent, and the most design freedom. The category people picture when they say 'ADU.'
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ConversionThe fastest, most affordable path — your existing garage footprint becomes a studio or one-bedroom. No new foundation, no new roof, dramatically less structure.
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AttachedAn addition off the main house with a separate private entrance. Shares structure and utility runs to cut cost while keeping the unit fully independent.
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JADUUp to 500 sq ft carved from inside the existing home with an efficiency kitchen. The lowest-cost way to create a rentable unit — often no exterior work at all.
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Two-StoryMaximizes livable square footage on a small lot footprint. More structure and more design, but the highest space-per-square-foot-of-yard you can get.
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Above GarageA unit built over a new or existing garage — you keep the parking and the yard, and add a full apartment above it.
See full pricing →California has spent several legislative sessions removing local barriers to ADUs. Here's the practical shape of it — and why local rules still matter.
Local governments cannot impose standards that make an otherwise-qualifying ADU infeasible. Cities still administer permits, but within limits the state defines.
Rear and side setback requirements for ADUs are constrained by statute, which is why units can sit far closer to property lines than a main-house addition could.
Additional parking generally can't be required for ADUs near transit or in several other defined situations — a common blocker that no longer applies to many lots.
Impact fees are restricted for smaller ADUs, which is why the size you choose has a bigger effect on total cost than square footage alone suggests.
An ADU generally can't be sold apart from the main house. It adds value and income to your property — it doesn't subdivide it.
Utility connections, fire access, height overlays, septic capacity, and historic districts are where projects actually get complicated. That's the work of a real feasibility study.
This is general information, not legal advice, and ADU rules change. We verify the current state and local requirements for your specific parcel as part of every feasibility review.
Milestones, not a two-year fog. You always know what happens next.
We confirm what your lot allows under state and local rules — and tell you plainly if it won't work.
Floor plan and siting tuned to setbacks, utilities, and how you'll actually use it.
Site plan, floor plan, elevations, structural, and energy coordination.
Submitted and coordinated with your city, with revisions handled until it issues.
We match you with licensed contractors, then you collect rent on a documented scope.
Follow one Southern California garage conversion end to end — the feasibility verdict, the layout decisions, the permit path, and the finished unit with a tenant in it. Real numbers, including the ones that didn't go to plan.
Construction is bid separately. This is what it costs to get a permittable ADU designed.
Full refund if your lot can't support an ADU
Revisions free until your permit is issued
Construction cost is separate and varies widely by type — garage conversions run dramatically less per square foot than detached new builds. The feasibility study gives you your real number.
"The feasibility report told me my septic capacity was the real constraint — something two builders had completely skipped over. Saved me from designing a unit I couldn't have connected."
"Garage conversion, permitted and rented in under a year. The cash flow projection they gave me at the start ended up within about a hundred dollars of what I actually collect."
"I liked that they'd tell me no. I'd talked to three design-build firms and every one of them said yes to everything."
Every number on this page — the feasibility verdict, the cost range, the payback period — exists to get you here: a finished unit with someone living in it, paying rent every month.
A 750 sq ft one-bedroom is the rental workhorse. It rents fastest, holds tenants longest, and earns the most per square foot of anything you can put in a backyard.
Not a list of features. The specific structural reasons the outcome is different.
| BestHouse | Design-build ADU companies | |
|---|---|---|
| Answer to "will my lot work?" | A verdict we refund if we are wrong | Yes, from everyone, always |
| Who checks septic and setbacks | Before you spend anything on design | Sometimes, eventually |
| What they show you | Cost, rent, cash flow, and payback | Build cost |
| Incentive to say no | We do not build, so no is free to say | None — they want the build |
| If the answer is no | Feasibility fee refunded in full | You already paid for design |
Tell us about your property and we'll come back with a real feasibility answer — including the parts other companies skip.
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