HELOC vs ADU Construction Loan | Arizona Casita Guide (2026)

In this Article

• What Is the Difference Between a HELOC and an ADU Construction Loan?
• What Does an ADU Cost to Build in Phoenix in 2026?
• HELOC Equity Limits vs. As-Completed Value: How Much Can You Borrow?
• How Do Draws and Inspections Work for HELOCs vs. ADU Construction Loans?
• Which Is Cheaper: An Arizona HELOC or an ADU Construction Loan?
• Why Are As-Completed Appraisals Harder in Arizona Right Now?
• HELOC vs ADU Construction Loan: Should You Choose for an Arizona Casita?
• Frequently Asked Questions

Summary of ADU Financing Options in Arizona

Feature	Home Equity Line of Credit (HELOC)	ADU Construction Loan
Value Lended Against	Current appraised value today	As-completed value (including finished casita)
Fund Release	Flexible self-draw line of credit	Lender releases funds in milestone draws
Site Inspections	None	Third-party inspection required before each draw
Contractor Rules	Unrestricted (Your choice)	Lender must approve General Contractor
Upfront Paperwork	Standard home equity underwriting	Plans, line-item budget, draw schedule, contract
Build-Phase Payments	Interest-only on drawn balance	Interest-only on disbursed balance
Post-Completion	Draw period ends; repayment begins	Converts to or refinances into permanent mortgage
Interest Rate Type	Typically variable (tied to Prime)	Typically fixed
Typical Credit Floor	~680	~700

What Is the Difference Between a HELOC and an ADU Construction Loan?

A HELOC lends against what your home is worth today, while an ADU construction loan lends against what it will be worth once the casita is built. Everything else that differs between them follows from that one mechanical distinction.

If your equity today covers the build, you never need the second column. If it does not, nothing in the first column will stretch far enough.

The practical difference is control:

• With a HELOC, the bank hands you a line of credit and stops paying attention. You pay your builder on whatever schedule the two of you agreed to.
• With a construction loan, the bank stays involved for the whole project, approves who is building it, and pays your contractor only after an inspector confirms each phase is actually finished.

Neither is better in the abstract as they solve fundamentally different capital problems.

What Does an ADU Cost to Build in Phoenix in 2026?

A detached casita in the Phoenix metro generally runs $120,000 to $350,000 or more, with per-square-foot pricing commonly quoted between $150 and $400. Attached units and garage conversions typically land lower than ground-up detached construction because the foundation and envelope already exist.

Arizona homeowners have more room to build than they did two years ago. House Bill 2720, signed in May 2024 and effective January 1, 2025, requires Arizona cities with populations above 75,000 to allow at least one attached and one detached ADU on single-family lots. House Bill 2928 extended a similar framework to county jurisdictions.

Between them, local zoning rules changed substantially across the state:

• ADUs must be permitted in single-family residential zones without requiring a special use permit or public hearing.
• Cities cannot require more than a 5-foot setback.
• Cities cannot impose ADU-specific off-street parking requirements.
• There is no familial relationship requirement (the unit does not have to house a relative).
• There is no owner-occupancy mandate.

Size limits still come from your city. In Phoenix, lots up to 10,000 square feet generally allow an ADU up to 1,000 square feet, capped at 75% of the main house’s floor area, so a 1,200 square foot house supports roughly a 900 square foot casita. Larger lots allow more. Confirm current limits with your city planning department before you design anything, and note that HOA rules may still impose aesthetic requirements even where the city cannot say no.

HELOC Equity Limits vs. As-Completed Value: How Much Can You Borrow?

Run your current equity against the project cost first, because that single calculation usually decides the product for you. Most Arizona lenders cap a HELOC’s combined loan-to-value (CLTV) at 80% to 85% of what the home appraises for today.

Consider a Phoenix home worth $520,000 with a $290,000 primary mortgage, building a $180,000 casita:

• HELOC Option (85% CLTV Cap): $442,000 maximum total borrowing allowed. Subtracting the $290,000 existing mortgage leaves $152,000 in available credit. Result: $28,000 short of project funding.
• Construction Loan Option (90% As-Completed Value): If the finished property appraises at $640,000, that valuation supports up to $576,000 of total lending. Subtracting the $290,000 existing mortgage leaves $286,000 in available borrowing. Result: Project fits with a $106,000 contingency cushion.

Now flip the scenario. On a $700,000 Scottsdale home with a $200,000 mortgage, an 85% HELOC yields $395,000 in borrowing capacity against that same $180,000 project. Equity is not the constraint, so accepting mandatory inspections, lender contractor vetting, and draw schedules adds unnecessary friction. The HELOC is the superior tool.

Underwriting Trap: Most traditional lenders will not count prospective ADU rental income toward debt-to-income (DTI) qualification without an executed lease or documented tax history on the property. While some specialized ADU lenders credit a percentage of projected market rent, verify this underwriting guideline directly before applying.

How Do Draws and Inspections Work for HELOCs vs. ADU Construction Loans?

A HELOC allows instant self-service access to funds without verification. A construction loan releases funds conditionally following third-party field inspections.

With a HELOC, you have a line of credit and you write the checks. Pay your contractor a deposit today and a progress payment next month on whatever terms you negotiated. No inspection, no approval, no waiting. You can also align your draws to the build so you are not paying interest on money sitting idle during permitting delays, which in Phoenix can be a meaningful stretch of time.

With a construction loan, the lender disburses on milestones. A representative schedule looks something like this:

• 10% at permit approval
• 25% at foundation completion
• 35% at framing and roof
• 25% at drywall and mechanical rough-in
• 5% at final inspection and certificate of occupancy

Percentages and milestones vary by lender, so treat that as a shape rather than a standard. Each release requires an inspection, which means scheduling, a fee, and a wait. If the inspector disagrees that a phase is complete, the draw does not release and your contractor does not get paid on time.

The oversight is a real benefit, not just friction. A third party is verifying that the work matches the plans and the pricing is reasonable before your money moves. If you have never run a construction project and do not have someone experienced advising you, that supervision is worth something. Homeowners who pick a contractor on price alone and skip reference checks are exactly the people the inspection process protects.

The honest framing is that a HELOC gives you speed and autonomy, and a construction loan gives you structure and a check on your builder. Which one you want depends on how confident you are managing a six figure build.

Which Is Cheaper: An Arizona HELOC or an ADU Construction Loan?

A construction loan often wins on rate and loses on fees, but the cost that actually decides it is whether the product makes you give up your first mortgage. HELOCs carry variable pricing tied to prime, so the payment moves. Construction loans are frequently fixed and can price competitively, sometimes at or below what a HELOC costs.

Compare on four things rather than one:

• Rate and rate type. A fixed construction loan removes the variability a HELOC carries over a multi-year build and payoff.
• Closing costs. A construction-to-permanent loan often covers both the build and the permanent financing in one set of closing costs. A HELOC has lower upfront costs but does not replace your mortgage.
• Inspection and administrative fees. Construction loans carry per-draw inspection costs and sometimes monthly monitoring fees. Budget for them.
• What happens to your first mortgage. This is the big one. A HELOC sits behind your existing mortgage and leaves it untouched. Some construction-to-permanent products replace your first mortgage entirely. If you are carrying a rate from 2020 or 2021, giving it up to build a casita is usually a bad trade regardless of what the construction loan quotes.

That last point decides the question for a lot of Valley homeowners. Protecting a low first mortgage rate is often worth more than any difference in construction financing terms.

Splitero requires no income verification and pre-qualifying takes about two minutes without affecting your credit. Be clear-eyed about the tradeoff: you give up future appreciation, and an HEI is not fast enough for a true emergency either, so it belongs in the same planning conversation as the HELOC rather than the panic one.

Why Are As-Completed Appraisals Harder in Arizona Right Now?

Arizona legalized ADUs faster than the market produced the sales data needed to value them. An as-completed appraisal has to be supported by comparable sales, and a comparable sale means a home with a similar accessory unit that actually sold nearby and recently.

Statewide ADU rights only took effect in January 2025, with county coverage following. Before that, most Arizona cities made these units difficult or impossible to build. That means the inventory of Phoenix-area homes with permitted ADUs that have changed hands is still thin in many neighborhoods, and thin comps make it harder for an appraiser to justify the number your construction loan depends on.

The consequence is specific and worth planning around. The homeowner who most needs as-completed underwriting, the one whose current equity does not cover the build, is also the one most exposed if the as-completed value comes back lower than the project assumed. A short appraisal can shrink your loan below what the casita costs, mid-project.

Three ways to reduce that risk:

• Ask your lender which appraiser pool they use and whether those appraisers have valued ADU projects in your area. Experience with the property type matters more than usual here.
• Have your contractor or agent pull recent nearby sales with permitted accessory units before you apply, so you know whether the comps exist rather than finding out at underwriting.
• Build a contingency into your financing, not just your budget. If your loan is sized to the exact project cost, you have no cushion for either an appraisal shortfall or a construction overrun.

This should improve as more Arizona ADUs are built and resold. Right now it is a real constraint on the product that is supposed to solve the equity problem.

HELOC vs ADU Construction Loan: Which Should You Choose for an Arizona Casita?

Choose based on what you are short on: equity points you to a HELOC, and a shortage of it points to a construction loan. Here is the practical decision path.

Choose a HELOC if:

• Existing home equity covers the total construction budget plus contingencies.
• Preserving your low primary mortgage interest rate is a priority.
• You are comfortable managing builder payments and progress monitoring independently.
• You require drawdown flexibility to avoid paying interest during municipal permitting delays.

Choose an ADU Construction Loan if:

• Existing home equity is insufficient to cover total construction costs.
• The casita is a ground-up detached build exceeding $250,000–$300,000.
• You prefer fixed-rate financing over variable rate exposure during the build phase.
• You require mandatory third-party oversight of contractor milestones and disbursements.

Verification Note: Verify that your general contractor holds an active license with the Arizona Registrar of Contractors at azroc.gov prior to executing contracts.

A hybrid is common and legitimate. Some homeowners use a HELOC for design, permitting, and early soft costs, then move to construction financing or refinance once the project is defined and the value is established. Just lock your financing path before construction starts, because switching products mid-build causes delays in draws and inspections.

Whichever you choose, confirm your builder holds a current Arizona Registrar of Contractors license at azroc.gov before signing anything.

For a deep dive on how Arizona’s HB 2720 impacts casita equity and property tax caps, read our Arizona Casita Financing Guide.

HELOC vs ADU Construction Loan: Frequently Asked Questions

EquitySquirrel is an educational resource operated by Scout Media LLC, not a lender, contractor, or law firm. This content does not constitute financial, legal, or construction advice. Construction costs, lending terms, appraisal outcomes, and municipal ADU rules vary and change; confirm all current figures and local requirements directly. Cost figures are metro estimates, not a quote for any specific property. Statements about Arizona ADU legislation are general background and not a legal opinion; confirm current requirements with your city or county planning department. Verify Arizona ROC licensing at azroc.gov before hiring any contractor. Consult a licensed financial professional before making decisions about your home equity. Aleksandra Kadzielawski, Lic #SA694336000.