How much does it cost to finance an ADU in 2026?

ADU construction costs average $100,000–$300,000 depending on type: garage conversion ($30,000–$80,000), basement conversion ($50,000–$120,000), attached addition ($80,000–$180,000), detached cottage ($120,000–$300,000). Best financing: HELOC at 7.5–9.5% variable, or home equity loan at 8.25–9.5% fixed. Cash-out refinance makes sense if your current rate is under 5.5%.

Can I use a HELOC to build an ADU?

Yes — a HELOC is one of the best ADU financing options in 2026. You only draw what you need (reducing interest cost during construction), rates are 7.5–9.5% variable, and you need 15–20% equity remaining after the draw. Most HELOCs have a 10-year draw period and 20-year repayment. You need 680+ credit score and 80–85% combined LTV.

Will an ADU increase my home value?

Yes. Studies show ADUs increase home value by $100,000–$200,000 in high-cost markets, and $50,000–$100,000 in median markets. More importantly, ADUs generate rental income averaging $1,500–$2,500/month. A $150,000 ADU that rents for $1,800/month delivers a 14.4% gross yield — far exceeding stock market returns.

Can ADU rental income help me qualify for the loan?

For construction loans, lenders may use projected future rental income. For HELOC and home equity loans, they use your existing income. Once the ADU is rented and has 12–24 months of history, you can count 75% of rental income on future refinance applications (Fannie Mae rules).

What is the cheapest way to finance an ADU?

Cheapest option depends on your situation: (1) If you have a low-rate mortgage (under 5%), keep it and use a HELOC for ADU construction. (2) If rates are similar to your current mortgage, cash-out refinance simplifies to one payment. (3) California homeowners: check CalHFA ADU Grant ($40,000 free money). (4) For small garages/basements: RenoFi loans at 6.5–8.5% based on post-renovation value.

ADU Financing 2026: 6 Loan Options Ranked — HELOC Wins for Most Homeowners

ADU Construction Costs by Type (2026)

ADU Type	Cost Range	Build Time	Best Financing
Garage Conversion	$30K–$80K	4–8 months	HELOC or Home Equity Loan
Basement Conversion	$50K–$120K	3–6 months	HELOC or Cash-Out Refi
Attached Addition	$80K–$180K	6–12 months	Cash-Out Refi or Construction Loan
Detached Cottage	$120K–$300K	8–14 months	Construction Loan → Perm
Prefab/Modular	$80K–$160K	3–6 months	HELOC or Home Equity Loan

All 6 ADU Financing Options Ranked (Cheapest First)

HELOC7.5–9.5%Variable

Best for: Low-rate existing mortgage holders | Limit: Up to 85% CLTV

Pro: Only pay interest on what you drawCon: Variable rate risk

Home Equity Loan8.25–9.5%Fixed

Best for: Prefer predictable payments | Limit: Up to 85% CLTV

Pro: Fixed rate, lump sum at closeCon: Higher rate than HELOC if prime drops

Cash-Out Refinance6.45–7.25%Fixed

Best for: Current rate above 6% | Limit: 80% LTV on new loan

Pro: Lowest rate, one paymentCon: Resets mortgage clock, closing costs ~$5K

Construction Loan7.5–10%Variable → Fixed

Best for: Detached ADU from scratch | Limit: Based on after-value

Pro: Draws match build scheduleCon: Higher rate, 2 closings required

FHA 203(k)6.5–7.0%Fixed

Best for: Buying + building ADU at once | Limit: FHA loan limits by county

Pro: Renovation + purchase in one loanCon: 3.5% down, MIP required, property rules

Personal Loan9.5–18%Fixed

Best for: Small garage/basement ADU only | Limit: $50,000 typical max

Pro: Fast approval, no equity neededCon: Expensive, short term = high payment

The Math: Does an ADU Actually Make Financial Sense?

Let's run the numbers on a $150,000 garage-to-cottage conversion using a HELOC at 8.5% (current average).

$150K ADU — 10-Year ROI Analysis

HELOC payment (8.5%, 10yr):

-$1,860/mo

ADU rental income:

+$1,800/mo

Net monthly cost:

-$60/mo

Home value increase:

+$120K–$200K

10-year total rental income:

+$216,000

At just $60/month net cost, you're essentially building $150,000 in equity and collecting $216,000 in rental income over 10 years. Get HELOC quotes for your ADU project to see your exact break-even timeline.

Ready to Finance Your ADU?

Compare HELOC, home equity loans, and cash-out refinance rates from multiple lenders in one place. No hard credit pull to start.

Compare HELOC Rates Get Home Equity Loan Quotes

HELOC vs Cash-Out Refinance for ADU: Side-by-Side

Factor	HELOC	Cash-Out Refi
Rate (May 2026)	7.5–9.5% variable	6.45–7.25% fixed
Closing costs	$500–$1,500	$5,000–$12,000
Keeps current mortgage?	YES	NO — replaces it
Best if current rate is…	Under 5.5%	6.0% or higher
Payment during construction	Interest only on draws	Full P&I from day 1
Flexibility	Draw as needed	Lump sum at close
ADU rental income counted?	Not immediately	After 12–24 months

How to Qualify: What Lenders Check for ADU Loans

Credit score: 680+ for HELOC/HE loan, 620+ for FHA 203(k), 700+ preferred for construction loans
Equity: 15–20% remaining after the ADU loan (so if home = $500K, you can borrow up to $400K–$425K combined)
DTI: Back-end DTI under 43% (Fannie/FHA), up to 50% with strong compensating factors
Plans and permits: Construction and land loans require approved permits and contractor bids
Appraisal: Lender will appraise current value + ADU contribution to ensure sufficient equity

State-Specific ADU Grants (Free Money First)

Before taking any loan, check these programs:

California CalHFA ADU Grant: Up to $40,000 — no repayment required for low-to-moderate income homeowners
Oregon ADU Initiative: Portland offers $10,000–$30,000 low-interest loans specifically for ADUs
Washington State: Some counties offer ADU pre-approved permit programs + fee waivers
Federal weatherization: If ADU includes energy efficiency improvements, additional federal grants may apply

Exhaust free grants before taking on debt. Even $20,000 in grants reduces your HELOC draw by $20,000, saving $1,700/year in interest at 8.5%.

ADU Financing 2026: 6 Ways to Fund a Guest House or Rental Unit

Quick Answer: Which ADU Loan Wins in 2026?