ADU Construction Loans 2026: Every Way to Finance One

What lenders mean by an ADU

An accessory dwelling unit is a second, smaller home on the same lot. Fannie Mae's Guide says it must “be on the same parcel as the primary one-unit dwelling,” be subordinate in size, and have its own entrance, kitchen, sleeping area, bathing area and bathroom. It can be site-built or factory-built, including modular, and the examples are a living area over a garage, in a basement, a small addition, or a manufactured home classified as real property. Freddie Mac's February 2026 fact sheet adds that one ADU is allowed on a 1-, 2- or 3-unit property and that it must comply with zoning: legal, legal non-conforming, or in a place with no zoning. FHA's Mortgagee Letter 2023-17 says a one-unit property with a single ADU remains a one-unit property.

The first thing to check is the count. The Fannie Mae Guide topic we read says only one ADU is permitted on the parcel and none with a two- to four-unit dwelling. Announcement SEL-2025-10 of December 10, 2025 expanded that: up to three ADUs on a one-unit property, and ADUs on two- to three-unit properties as long as the total does not exceed four units. It took effect March 31, 2026 and applies only to lenders using the UAD 3.6 policy. The lender you call may be on either version, so ask before you design a second unit.

The options side by side

ADU financing options and what the sources say (October 26, 2026)

Renovation mortgages: HomeStyle and CHOICERenovation

These two are the only products in our list written for a loan that includes the building work. You borrow once, the lender holds the renovation money in escrow and pays the contractor as work is inspected, and the appraiser values the property as if the work were finished. Fannie Mae's Guide says the appraisal “must provide an ‘as completed’ appraised value,” and the plans and specifications must be prepared by a registered, licensed or certified general contractor, renovation consultant or architect. All work must be done by a licensed contractor or subcontractor unless licensing does not apply. Fannie Mae gives 15 months from closing to finish; Freddie Mac gives 450 days from the Note Date and requires a contingency reserve of at least 10% and at most 20% of the renovation cost.

Two limits matter for an ADU. The first is the line between an accessory unit and a second house. Fannie Mae's HomeStyle FAQ says an accessory unit “may be detached from the primary dwelling” and also says funds “may not be used to construct another residential dwelling on the property.” Both sentences are on the same page, so the lender decides how your design is classified; get that answer in writing before you pay an architect. Freddie Mac's December 2024 fact sheet says proceeds “must only be used to finance renovations that are made to an existing dwelling” and may not be used “to raze an existing structure and build a new dwelling,” while its February 2026 ADU fact sheet says CHOICERenovation can be used to construct a new ADU. The second limit is the loan-to-value on the as-completed value: 75% for a one-unit investment property and 90% for a second home on a HomeStyle limited cash-out refinance in Fannie Mae's August 5, 2026 matrix, and the borrower on that loan cannot receive cash proceeds.

Hypothetical HomeStyle refinance on a one-unit investment property (our arithmetic, not an offer)

The example shows how the as-completed value drives the answer: at a finished value of $650,000 the loan limit leaves $107,500 against the build in this case. It also shows the trap. The $107,500 has to cover the ADU and the closing costs, so a $150,000 build would leave a gap of at least $42,500 in this example. We did not read Fannie Mae's appraisal section on ADUs, so how the appraiser values the added unit is not verified.

FHA 203(k): the owner-occupant version

HUD's 203(k) program lets a buyer or owner finance purchase and rehabilitation in one FHA loan. The Standard 203(k) “supports major renovations and structural additions,” requires at least $5,000 of rehabilitation, and the total value must fit the FHA mortgage limit for the area. Mortgagee Letter 2023-17, effective October 16, 2023, lists among Standard 203(k) improvements “converting a one-family Structure to a one-family Structure with an ADU,” “adding an Accessory Dwelling Unit (ADU) that will be attached to an existing Structure” and “renovating an existing ADU that is attached or unattached.” The list is introduced as “include, but are not limited to,” so a new detached ADU is not excluded in terms, but it is not named either. We read the 2023 letter and HUD's program page, not the current Handbook 4000.1 text, so check the current rule with an FHA lender.

The Limited 203(k) lets homeowners finance up to $75,000, but HUD describes it as for “minor remodeling and non-structural repairs,” which does not describe building an ADU. The same letter says that on an FHA cash-out refinance, rental income from an ADU “cannot be used as Effective Income to qualify,” so do not plan on the ADU's rent to qualify.

HELOC, home equity loan and cash-out refinance

For many owners with a low-rate first mortgage, a second loan is the obvious route, It is also the option with the least ADU-specific rule in the pages we read. The CFPB describes a HELOC as “an ‘open-end’ line of credit that allows you to borrow repeatedly against your home equity,” with a draw period that “could last 10 years, for example,” followed by a repayment period in which “monthly payments are often significantly higher.” It says HELOCs usually have a variable rate and that if you fall behind, “you could lose your home.” The FTC says the lender “may freeze or reduce your line of credit in certain situations,” that an interest-only home equity loan usually ends in a balloon payment, and that for a main residence you can cancel within three business days for any reason. A construction budget that draws over a year or more is exactly the situation where a frozen line hurts: if the line is cut mid-build, the foundation is poured and the money is not there.

A cash-out refinance replaces the first mortgage. On Fannie Mae's matrix the maximum is 80% LTV for a one-unit principal residence and 75% for a one-unit investment property. The existing first mortgage must be at least 12 months old, and at least one borrower must have been on title for six months. A hypothetical: at 80% of a $600,000 value the maximum loan is $480,000, which after a $300,000 mortgage leaves $180,000 before costs (our arithmetic). The sources we read do not say whether a lender counts the future ADU in that value, so ask what value the lender will use. Compare the new rate on the whole balance with the old rate, not just the cost of the new money, and see our HELOC on investment property and cash-out refinance on investment property pages for the rental side.

Construction-to-permanent loans: usually the wrong tool for an ADU

A construction-to-permanent loan is written for building a house on a lot. Fannie Mae's overview says it is a long-term mortgage granted “for the purpose of replacing interim construction financing that the borrower has obtained to fund the construction of a new residence,” and the borrower “must hold title to the lot.” The single-closing form allows no more than 18 months in total. If you are adding an ADU to a house that already has a mortgage, that is not the situation the text describes. If you are building a primary home and an ADU together on a vacant lot, see our construction-to-permanent loan rules.

Building an ADU as an investor

If the ADU is for a property you do not live in, the investor construction lenders are the other door. Kiavi's construction page says it offers “Loans from $150K to $10MM,” “Up to 85% of total costs” (“purchase price + construction costs”) and “Up to 70% of ARV (after-repair-value),” supports single-family residences, 2-4 plexes and PUDs, and that “appraisals are not required for closing.” It also says: “Non owner-occupied rental properties only.” The page does not mention ADUs, so we cannot tell you whether an ADU on an existing rental, on its own, fits; the question for Kiavi is whether the project is a new build on a lot you are buying or already own, or a rehab. For the cap arithmetic and the other lenders, see our ground-up construction loan page.

Hypothetical Kiavi caps on a purchase plus an ADU-style build (lender claim, our arithmetic)

Kiavi pays us a referral fee when a loan closes through its button below. Its page is for rental properties, so a homeowner building a unit to live in or for a relative should skip this box; an owner of a rental who is also buying the property is the reader it fits. Lima One and RCN pay us nothing. Everything above, including the other options, is the same either way.

The California grant: closed, as far as we can read

CalHFA's ADU Grant Program paid “grants up to $40,000 to reimburse pre-development and non-recurring closing costs associated with the construction of an ADU,” such as site prep, architectural designs, permits, soil tests, impact fees, surveys and energy reports. The program page, in an Internet Archive capture of October 2, 2026, carries one update: “December 28, 2023 - The latest round of ADU funding has been fully allocated.” It adds: “If anyone approaches you saying they can help you get an ADU Grant, it is a financial scam.” Our connection to calhfa.ca.gov was refused on October 26, 2026, so we could not read the live page, and we have not verified that no new round has opened since the capture. Check calhfa.ca.gov directly, and treat any paid service promising a grant with the CalHFA warning in mind.

What you can do with this

1. Decide which side of the line you are on. An owner who will live on the property has the renovation mortgages, 203(k), a HELOC and a cash-out refinance. A landlord has the investor construction lenders; whether home equity loans are available on a rental depends on the lender (see our HELOC on investment property page).
2. Ask three questions before you design. How many ADUs the lender allows on your property type (one, or up to three under the UAD 3.6 policy), whether a detached unit counts as an “accessory unit” or as “another residential dwelling,” and what value the appraiser will use.
3. Price the second-loan risk. With a HELOC, ask whether the line can be frozen or reduced, what happens when the draw period ends, and what the rate adjusts to. With a cash-out refinance, compare the rate on the whole new balance with your current one.
4. Budget the contingency. Freddie Mac requires 10% to 20% of renovation costs in reserve; a build with no reserve is the one that stalls.
5. Check zoning before the loan. Freddie Mac requires an ADU to be legal, legal non-conforming or in a location with no zoning, and Fannie Mae's HomeStyle says structures must follow local zoning and building codes.
6. Do not count on grant money. The CalHFA program said its funds were fully allocated on December 28, 2023.

FAQ

Sources: Fannie Mae Selling Guide topics B2-3-04, B2-1.3-03, B5-3.1-01, B5-3.1-02, B5-3.2-01, B5-3.2-02 and B5-3.2-03, announcement SEL-2025-10, the HomeStyle Renovation FAQ and the Eligibility Matrix of August 5, 2026 (fanniemae.com); Freddie Mac CHOICERenovation fact sheet (December 2024) and Accessory Dwelling Units fact sheet (February 2026) (freddiemac.com); HUD Mortgagee Letter 2023-17 and the 203(k) program page (hud.gov); CFPB, “What is a home equity line of credit (HELOC)?” (Internet Archive copy of October 12, 2026); FTC, “Home Equity Loans and Home Equity Lines of Credit” (Internet Archive copy of October 15, 2026); Kiavi's New Construction / Infill Loans page (kiavi.com), read October 26, 2026; CalHFA's ADU Grant Program page, Internet Archive capture of October 2, 2026. Every figure, quote and link is in the downloadable CSV, one source per row. Examples are hypothetical arithmetic, not offers. This is analysis of public documents, not investment, legal, tax or lending advice, and not a loan offer.