Adu Information - Legacy Homes

The Basics

What is an ADU?

An Accessory Dwelling Unit (ADU) is a secondary housing unit on a single-family or multifamily residential lot. California currently recognizes four distinct types.

Detached ADU

A standalone structure completely separate from the main home. Placed anywhere on the lot within setback requirements — maximum privacy, flexibility, and independence for both households.

Up to 1,200 sq ft 4 ft setbacks Most popular type4backs

Attached ADU

An addition to your existing home that shares at least one wall. Typically less expensive to build since it shares foundation and utility connections. Has its own separate entrance.

Up to 50% of home size Shared foundation Lower build cost4backs

Garage Conversion

Convert an existing attached or detached garage into fully permitted living space. The most cost-effective ADU type — the structure already exists, so you mainly pay for interior finish work.

Lowest cost option 0 ft setbacks allowed Fastest timeline4backs

Junior ADU (JADU)

Created within the existing walls of your primary home — no new construction required. Capped at 500 sq ft. Requires owner occupancy on-site, but has the simplest permitting process and lowest fees.

Max 500 sq ft No new construction Lowest permit fees4backs

Why California homeowners are building ADUs now

Recent state legislation (AB 2221, SB 9, and others) has dramatically simplified ADU permitting. Cities must approve ADUs ministerially — no public hearings, no discretionary review. Fees have been capped and parking requirements removed near transit. This is the best environment for ADU construction California has ever seen.

State Law

California ADU Regulations

State law sets the floor — cities can be more permissive but not more restrictive. Here's what the state currently allows.

1,200

Max sq ft (detached)

4 ft

Min rear & side setback

$0

Impact fees under 750 sq ft

2

ADUs allowed per lot

Maximum Size

Detached ADUs may be up to 1,200 sq ft. Attached ADUs can be up to 50% of the primary home's floor area. JADUs are capped at 500 sq ft.

Setbacks

New detached ADUs must maintain 4 ft rear and side setbacks. Converted existing structures (garages) can be 0 ft from rear and side property lines.

Height Limits

Up to 16 ft for detached ADUs in most cases. Up to 18 ft if within ½ mile of public transit. ADUs above garages may be taller depending on the city.

Parking

No parking replacement is required when a garage is converted to an ADU. ADUs within ½ mile of public transit require no additional parking spaces.

Owner Occupancy

Not required for standard ADUs built after January 1, 2020. Only required for JADUs. Rental of both the primary home and ADU is allowed simultaneously.

Permit Fees

Impact fees are waived for ADUs under 750 sq ft. For larger ADUs, fees must be proportional to primary home fees — cities cannot charge disproportionate amounts.

Money Matters

Financing Your ADU

ADUs typically cost $150,000–$350,000 depending on size, type, and finishes. These are the most common financing options California homeowners use.

Cash-Out Refinance

Refinance your primary mortgage to pull out equity as cash. Works well if you have substantial home equity and current rates are favorable. Replaces your existing mortgage.

Home Equity Line of Credit (HELOC)

A revolving credit line secured by your home's equity. Draw funds as needed during construction. Variable rate — the most popular ADU financing option in California.

Construction Loan

A short-term loan that covers construction costs, then converts to a permanent mortgage. Requires detailed plans and a qualified contractor or project manager.

ADU-Specific Programs

Several California programs offer ADU-specific financing including the CalHFA ADU Grant Program offering up to $40,000 for qualifying homeowners.

Return on Investment Example

A well-built ADU generates rental income for decades while adding significant equity to your property. Here's a typical Central Valley scenario.

Build Cost (600 sq ft ADU)$180,000

Monthly Rental Income+$1,400/mo

Annual Gross Income$16,800/yr

Property Value Added+$180,000+

Break-Even Timeline~15 years

What to Expect

Typical ADU Timeline

From your first call to move-in — here's what to expect. Times vary by city and project complexity.

1

1–2 Weeks

Feasibility Assessment

Site visit, zoning review, utility analysis, and project scope. We deliver a written feasibility report with cost estimates and recommendations for your specific property.

2

4–8 Weeks

Design & Construction Documents

Schematic design, floor plan selection, interior design, and full construction document preparation including Title 24 energy compliance reports.

3

6–16 Weeks

Permitting

Plan submittal, city review (30–60 days by law), corrections response, and permit issuance. Timeline varies by city workload. We manage the entire process.

4

4–9 Months

Construction

Site prep, foundation, framing, MEP rough-in, exterior finishes, interior finishes, and all inspections. Final Certificate of Occupancy issuance. You have a tenant-ready unit.

Total typical timeline: 9–18 months from first call to move-in. Garage conversions are often faster at 6–12 months. JADUs can be as fast as 4–8 months total.

Common Questions

Frequently Asked Questions

Do I need a general contractor to build an ADU?

Not with Legacy Homes. We serve as your project manager, sourcing and managing all subcontractors. You get the expertise of a GC without paying GC markup fees.

Can I rent out my ADU as a short-term rental (Airbnb)?

It depends on your city's short-term rental ordinance. Some cities allow it, others restrict it. We can help you understand your city's rules before you build.

Will an ADU increase my property taxes?

Yes — the ADU will be assessed and added to your assessed value. However, the increase is typically much smaller than the equity gained. Your primary home's assessed value is not reassessed.

How much does an ADU cost to build?

In California's Central Valley, detached ADUs typically range from $150–$250 per sq ft all-in. A 600 sq ft studio runs roughly $100,000–$150,000. Garage conversions start around $60,000–$100,000.

Can my HOA block me from building an ADU?

No. California law (Civil Code §4751) prohibits HOAs from unreasonably restricting ADU construction. HOAs can impose reasonable aesthetic guidelines but cannot outright prohibit ADUs.

What's the difference between a JADU and a regular ADU?

A JADU (Junior ADU) is created within the existing walls of your primary home and is capped at 500 sq ft. It requires the owner to live on-site. Regular ADUs can be detached and up to 1,200 sq ft.

How many ADUs can I build on my property?

California law allows up to two ADUs per single-family lot — one standard ADU and one JADU. Multifamily properties may allow more units depending on the number of existing units.

Everything you need to know about ADUs in California.