Accessory dwelling units (ADUs) — granny flats, in-law suites, garage conversions, backyard cottages — are one of the fastest-growing segments in residential real estate. California alone permitted roughly 25,000 ADUs annually in recent years. Investors and homeowners are building them for rental income, multigenerational living, and property-value gains.
What is an ADU?
An ADU is a secondary dwelling on the same lot as a primary residence. Types include:
| ADU type | Description | Typical cost |
|---|---|---|
| Detached backyard cottage | Stand-alone structure behind main house | $150K–$350K+ |
| Garage conversion | Existing garage converted to living space | $80K–$180K |
| Basement / attic conversion | Interior conversion within primary structure | $60K–$150K |
| Attached addition | New square footage attached to primary home | $120K–$280K |
| Prefab / modular ADU | Factory-built unit delivered and installed | $100K–$250K |
The American Planning Association ADU guide tracks state and local policy trends driving adoption nationwide.
Why ADU demand is surging
Housing shortage. The U.S. underbuilt housing for a decade after 2008. ADUs add density without new land — a politically palatable way cities increase supply.
Rental income. A permitted ADU in a high-rent market can generate $1,200–$3,500+/month depending on size and location. That income supports DSCR financing at 5.75%–10.5% on the combined property once stabilized.
Multigenerational living. Aging parents, adult children, and caregivers occupy ADUs while maintaining privacy — a demographic trend the Pew Research Center documents in multigenerational household growth.
State preemption laws. California, Oregon, Washington, and other states passed laws limiting local ADU bans. California’s ADU statutes effectively require most cities to allow at least one ADU per single-family lot.
Property value increase. Appraisers often credit permitted ADU square footage at 50–80% of primary-home value per square foot — a meaningful ARV bump on refinance.
ADU economics for investors
Investors use ADUs in three strategies:
House hack. Owner-occupant lives in the primary unit; ADU rent offsets the mortgage. Conventional owner-occupied financing may apply to the primary — ADU construction often uses renovation or construction loans.
BRRRR on SFR + ADU. Acquire a property with ADU potential, permit and build the unit, stabilize combined rent, refinance on total ARV. Bridge the construction phase on hard money at 8.99%–13.5%; exit to DSCR once both units are leased.
STR / mid-term rental. Some markets allow ADU short-term rental at premium nightly rates. Check local STR ordinances before modeling income — see short-term rental laws for investors.
Worked example: Los Angeles detached ADU
| Line item | Amount |
|---|---|
| Existing SFR value (as-is) | $850,000 |
| ADU construction cost | $220,000 |
| All-in basis | $1,070,000 |
| Post-ADU appraised value | $1,280,000 |
| Primary rent | $3,200/mo |
| ADU rent | $2,400/mo |
| Combined rent | $5,600/mo |
| DSCR at 75% LTV, 7.25% | ~1.15 on combined PITIA |
City-specific guides: top 5 cities to build ADUs · ADU zoning basics Chicago · worried about ADU zoning in Miami
Financing ADU construction
Most ADUs require construction or renovation capital before they generate income:
| Phase | Typical product | Rate band |
|---|---|---|
| Acquisition + ADU build | Hard money / fix-and-flip | 8.99%–13.5% |
| Stabilized hold (both units rented) | DSCR | 5.75%–10.5% |
| Owner-occupied house hack | Conventional / FHA (ADU income may count) | Market rates |
Jaken Finance Group funds non-owner-occupied investment property ADU projects where ARV and exit support the file. See rehab loans for investment property and fix-and-flip loan requirements.
Zoning and permit checklist
Before breaking ground:
- Confirm ADU allowance on your zoning district — city planning department or online GIS
- Review setback, height, and size limits — many cities cap ADUs at 800–1,200 sq ft
- Obtain building permits — unpermitted ADUs fail appraisal and DSCR refi
- Check HOA restrictions — CC&Rs may ban ADUs even where city allows them
- Plan utility connections — separate meter vs. sub-meter affects lease structure
Is an ADU right for your property?
ADUs work best where rents justify construction cost, zoning permits the unit, and your exit (hold or sell) captures the ARV premium. Markets with restrictive STR rules may still support long-term ADU leases at strong DSCR.
Questions about financing an ADU project? Pre-qualify · submit a flip scenario · (833) 264-7776
ADU popularity drivers — financing each strategy
| Strategy | Product | Rate band |
|---|---|---|
| Garage conversion ADU | Hard money / rehab | 8.99%–13.5% IO |
| Detached new build ADU | Ground-up or rehab | 8.99%–13.5% IO |
| ADU + hold primary | HELOC / personal | Not investor product |
| ADU on rental — add unit | BRRRR then DSCR | 5.75%–10.5% permanent |
Zoning is local — Chicago ADU basics · Miami ADU zoning · Ohio ADU guide · rehab loans.
Rates, terms and conditions offered only to qualified borrowers and are subject to change at any time without notice. Closing times are in business days and commence upon satisfaction of borrower conditions. All loans are subject to full underwriting for loan approvals. Jaken Finance Group only finances non-owner occupied investment properties.
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