What is the typical cash-on-cash yield on a California ADU?

After realistic vacancy, management, maintenance, insurance, and property tax additions, expect 8 to 11 percent cash-on-cash before financing in LA County. Bay Area runs 9 to 13 percent. Sacramento and Inland Empire run 5 to 8 percent. After mortgage debt service, cash flow is positive but modest (typically 2-5 percent yield).

How much does a permitted ADU add to home resale value?

In California, 30 to 60 percent of build cost is added to appraised value, based on 2025-2026 sales data from LA, Bay Area, and San Diego. The exact lift depends on neighborhood comp activity and ADU quality. Greater Seattle ADU resale lift runs slightly lower (25-50 percent of build cost) because the rental market is less mature.

Is the property tax increase a deal-breaker?

No, but it is meaningful. On a $260,000 build, expect an additional $2,600 per year in California property tax. Factor it into NOI calculations from day one. Washington property tax assessment is more variable; some counties reassess immediately, others on the next regular cycle.

How long does ADU construction take in 2026?

A garage conversion takes 4 to 6 months from permit submission to certificate of occupancy. A detached new-build ADU takes 8 to 14 months total: 2 to 4 months of design and permitting, 4 to 8 months of construction, 1 month of final inspections. Prefab modular ADUs can shorten construction to 3 to 5 months but require significant site prep first.

Can I rent my ADU on Airbnb?

Depends on local short-term rental laws. Los Angeles requires Home-Sharing Ordinance registration (only owner-occupied properties qualify, ADU eligibility varies). San Diego and most coastal CA cities have stricter limits. Seattle requires a short-term rental license. Verify specific city rules before assuming Airbnb is an option. Long-term rental (12+ month leases) is allowed everywhere ADUs are permitted.

What is the difference between an ADU and a JADU?

An ADU (Accessory Dwelling Unit) is up to 1,200 square feet in California, can be detached or attached, has its own kitchen and bathroom, and can be rented separately. A JADU (Junior Accessory Dwelling Unit) is up to 500 square feet, must be within the existing footprint of the primary residence, and shares some utilities. JADUs are cheaper to build at $40,000 to $90,000.

Do I need a separate utility meter?

Required for sub-metering separately billed tenants. Most California cities allow combined metering with internal sub-meters or include utilities in rent. Separate metering adds $4,000 to $12,000 to install (gas, electric, water connections). Most ADUs we track use a single combined meter and include utilities in the lease price.

How do I find a qualified ADU builder?

Look for builders with 10+ completed ADUs in your specific city in the past 24 months. Verify license: California CSLB B or B-2 (residential), Washington L&I active registration. Ask for permit-to-completion timeline (under 10 months is good). Get itemized bids from 2 to 3 builders. The Renology matches homeowners with pre-vetted ADU specialists in their metro at no cost.

The Real ADU Rental Economics in 2026 (with Math)

Every ADU article you have read includes the same hopeful math: build a detached ADU for $250,000, rent it for $3,000 per month, gross yield of 14 percent, beat the stock market. The hopeful math is not wrong, but it is incomplete. Real ADU economics include three numbers that most articles skip and one number that changes the whole calculation.

The honest cost stack in 2026

An 800-square-foot detached ADU in 2026 costs $240,000 to $320,000 in California, $280,000 to $400,000 in Greater Seattle, $200,000 to $300,000 in Texas and Florida metros, and $320,000 to $500,000 in NYC and Bay Area. These ranges assume:

Site work and utilities: $25,000 to $60,000 (often understated in initial bids)
Permits and impact fees: $8,000 to $25,000 (varies dramatically by city)
Foundation: $15,000 to $35,000 depending on slope and soil
Shell, MEP, finish: $150,000 to $250,000 for the building itself
Landscaping and exterior: $5,000 to $20,000
Furnishing if renting furnished: $8,000 to $20,000

The line item most homeowners forget: property tax reassessment. In California, the new ADU square footage is assessed at current market rates and added to the property tax bill. On a $260,000 build, that is roughly $2,600 per year in additional property tax. Over 20 years, that is $52,000 in non-recoverable expense. Few ADU articles include this in the math.

Gross rent vs net operating income

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An 800-square-foot ADU rents in 2026 for:

Los Angeles County: $2,400 to $3,800 per month
Bay Area: $3,200 to $5,500 per month
San Diego: $2,200 to $3,400 per month
Greater Seattle: $1,800 to $2,800 per month
Austin: $1,800 to $2,600 per month
Sacramento, Inland Empire: $1,400 to $2,200 per month

Take the LA County midpoint: $3,100 per month, $37,200 per year gross. Now subtract the real expenses:

Vacancy: 8 percent ($2,976/yr)
Property management or your time: 10 percent ($3,720/yr)
Maintenance and repairs: $2,500/yr (average; spikes in years 7-10)
Additional insurance: $1,800/yr
Property tax addition: $2,600/yr
Utilities (if you cover any): $1,200/yr

Net operating income: roughly $22,400/yr. On a $260,000 build, that is an 8.6 percent cash-on-cash yield before financing. Add a 30-year mortgage at 7.5 percent on $200,000 of the build (assuming $60,000 down) and the cash flow drops to roughly $5,500/yr. The yield is still positive, but it is not the 14 percent gross-yield headline.

The number that changes the calculation

The honest ROI on an ADU is not the rental yield. It is the resale value lift on the entire property. A finished, permitted ADU with a certificate of occupancy adds 30 to 60 percent of build cost to the appraised value of the primary home in California, per appraiser data we have collected from 2025-2026 LA, Bay Area, and San Diego sales.

On a $260,000 ADU build, that is $80,000 to $155,000 of resale-value lift, on top of the rental cash flow. If you sell the home five years after the ADU is finished, the rental income covers a meaningful chunk of the build cost AND you recover most or all of the build at sale. The IRR climbs to 15 to 22 percent depending on the metro and assumption set.

Permit timelines: California vs Washington in 2026

California AB-68 caps permit review at 60 days for compliant applications. In practice, Los Angeles LADBS, San Diego DSD, San Jose, and Oakland all hit 60 to 90 days for typical detached ADUs. Smaller cities sometimes faster. Bay Area cities trend longer because of design review.

Washington HB-1110 (effective 2024) requires cities over 25,000 population to allow at least 2 ADUs per single-family lot, but does not impose 60-day permit timelines. Seattle SDCI runs 4 to 6 months for typical ADU permits. Bellevue and other Eastside cities run similar timelines.

Where the economics break down

Three scenarios where ADU economics turn negative:

Inland markets with low rents. If rent is below $1,500/month, the math gets tight even with the resale lift, especially after factoring property tax and management.
HOA-restricted properties. Some HOAs (especially in Orange County and parts of Bay Area) restrict short-term rental and require 12-month minimum leases, which kills the high-margin furnished-rental play.
Build cost overruns above 25 percent. ADU projects that go from $260k to $340k due to surprise site conditions or scope creep can push the economics from solid to break-even.

Garage conversions: the cheaper path

Converting an existing detached garage to an ADU costs $80,000 to $150,000, roughly half the cost of a new-build detached unit. The shell, slab, roof, and walls already exist. New work focuses on insulation, drywall, kitchen, bathroom, and electrical upgrade. Permit timelines are shorter because the structure already exists.

The trade-offs: garage conversions usually deliver 350 to 600 square feet vs 800+ for new builds. Rents reflect the smaller footprint (typically 60-75 percent of new-build rent). The cap rate often comes out similar; the absolute cash flow is smaller.

Financing in 2026: cash-out, HELOC, or construction loan

Three main paths. Cash-out refinance of the primary residence is the most common, leveraging current home equity. Rates run 6.75 to 7.5 percent in early 2026 for prime credit. HELOC offers flexibility but carries variable rates. ADU-specific construction loans from lenders like LendingHome and Renofi disburse at construction milestones; rates are typically 8 to 10 percent during construction, converting to a 30-year mortgage at substantial completion.

CalHFA also offers ADU grants of up to $40,000 for qualifying low-to-moderate income California homeowners. Verify income eligibility at the CalHFA ADU portal before assuming you qualify.

Who should build an ADU in 2026

Three buyer profiles where the math works almost certainly:

Long-term holders in major California metros who plan to stay 7+ years and want passive cash flow plus equity build
Multigenerational households using the ADU for parents or adult children, where rental income is a bonus on top of the primary use
Properties in transit-rich, high-rent neighborhoods (West LA, Berkeley, Capitol Hill Seattle) where rent above $3k/month is reliable

For other scenarios, run the numbers carefully. The Renology has detailed cost data and rental comps for every California and Washington metro we cover. Read our ADU Construction pillar guide, browse California city pages or Washington city pages for local data, or get matched with vetted ADU builders to start the conversation.