ADU Financing in Oregon: Clackamas County Guide

The short answer: ADU financing in Oregon almost always runs through an owner-occupied loan, because you live in the main house. The usual routes are a renovation mortgage that wraps the build into one loan, a cash-out refinance, or a home equity line. Both FHA and Fannie Mae now let projected ADU rent help you qualify, capped at 30% of your qualifying income. A DSCR loan does not work here, because it requires that you not live on the property.

ADU Financing in Oregon Starts With Who Lives on the Property

Before anyone talks about loan products, answer one question: are you going to live in the main house? For most of the people who call me about ADU financing in Oregon, the answer is yes. They own a home in Milwaukie or Oregon City, there is room in the back yard or over the garage, and the plan is to build a small unit and rent it out.

That plan is owner-occupied financing. You occupy the property, so the loan is priced and underwritten as a primary residence, which is the friendliest category there is. Down payment and equity requirements are lower, and the rate structure is better than anything on the investment side.

State law is on your side too. Oregon requires cities over 2,500 people and counties over 15,000 to allow at least one accessory dwelling unit on any lot with a detached single-family home inside the urban growth boundary, under ORS 197A.425. Two specific things a city may not do under that statute: it cannot require you to live in either structure, and it cannot make you build additional off-street parking for the unit. Those bans came from House Bill 2001 in 2019 and they are statutory, not guidance. Every city in my footprint is subject to them.

One caveat that matters more than it sounds. That protection covers a long-term rental. It does not cover a nightly one, and I get to that below.

Four Routes for ADU Financing in Oregon

There is no single loan called an ADU loan. What exists is a handful of ordinary products, each of which fits a different starting point. Here is how I sort them.

One detail worth flagging on the FHA side, because it decides the route for some projects. The list of improvements eligible under a Standard 203(k) includes adding an ADU that will be attached to the existing structure, converting a one-family structure into one with an ADU, and renovating an existing ADU whether it is attached or detached. Building a brand-new detached cottage in the back yard is not on that list. If your plan is a standalone unit at the rear of the lot, we look at HomeStyle, a cash-out, or construction financing instead.

Terms, eligibility, and program availability vary, and everything here is subject to underwriting approval and a full loan estimate.

How Projected Rent Counts in ADU Financing in Oregon

This is the part that changed, and a lot of people are still working from the old rules.

Both major channels now let rent from an accessory dwelling unit help you qualify on the home you live in. Under FHA Mortgagee Letter 2023-17, if there is no rental history on the unit yet, the lender uses 75% of the lesser of the fair market rent the appraiser reports or the rent in the lease. On a Standard 203(k), where the unit does not exist yet, that figure drops to 50%. Either way, the rental income counted from the ADU cannot exceed 30% of the total monthly effective income used to qualify you.

Fannie Mae opened the same door in its Selling Guide update dated October 8, 2025. Projected ADU rent may be used on a one-unit principal residence, on a purchase or a limited cash-out refinance only, from one ADU even if the property has more than one, and capped at 30% of total qualifying income. The income has to be supported by a Single-Family Comparable Rent Schedule, Form 1007, which is an appraisal add-on rather than a separate order. My guide to the home appraisal process in Clackamas County explains what the appraiser is doing on that visit.

Two limits inside all of that deserve their own sentence. FHA does not allow ADU rental income as effective income on a cash-out refinance, and Fannie's version is likewise limited to purchases and limited cash-out. So if your plan is to pull cash out to build and lean on the future rent to qualify, that combination generally does not work. You qualify on the income you have, then the rent shows up later as cash flow rather than as qualifying income.

One more practical item: when FHA rental income is being used to qualify on a one-unit property with an ADU, the reserve requirement is two months of principal, interest, taxes, and insurance after closing. Plan for that in the cash-to-close conversation rather than discovering it three days before signing.

System Development Charges Change What ADU Financing in Oregon Costs

Here is the local wrinkle that no national article about ADU financing in Oregon is going to tell you, and it moves more money than a quarter point of rate.

System development charges are the one-time fees a city collects when new construction connects to water, sewer, streets, and parks. On an accessory dwelling unit they are a real line item, and in this county they range from nothing at all to a five-figure number depending on which side of a city boundary your lot sits on.

Look at the top and the third row together. The same accessory dwelling unit, built to the same plans, costs nothing in system development charges in Lake Oswego and roughly $17,800 in Oregon City. That gap is larger than most of the variables people spend weeks agonizing over, and it is decided entirely by an address.

Get the actual number from the city before you finalize a loan amount. On a renovation mortgage the fees are part of the project budget, and a budget that missed a five-figure fee has to be reworked mid-process, which is exactly when reworking it is most painful.

The Ten-Year Covenant Behind Those Waivers

Read the condition column again, because both waivers are the same instrument and it is not free money.

Portland and Lake Oswego each waive the charges completely, and each conditions the waiver on a covenant recorded against your property that bars short-term rental use for ten years. In both cases the restriction covers not just the new unit but any other structure on the lot, so it reaches the main house as well. Portland's clawback is specific: violate it and the exempted charges become immediately due at 150% of the rates in effect when the violation is identified.

So this is a choice, not a stack. Take the waiver and the nightly rental exit is closed for a decade, on the whole property. Keep that exit open and you pay the charges. There is no wrong answer, but there is a wrong time to think about it, and that is after the covenant is recorded.

The reason cities can do this at all is the second half of the same statute that protects you. ORS 197A.425 bars owner-occupancy and extra parking requirements for an ADU, then carves out vacation occupancies in subsection 2. An ADU rented long-term is protected. The same unit rented by the night is not, and the city is free to regulate it. That carve-out is the hinge, and my guide to short-term rental rules in Clackamas County sorts what each city does with the authority.

These are land-use and tax questions rather than lending questions, so run the specifics past your own attorney and CPA before you sign anything that records against your title.

Why a DSCR Loan Is Not ADU Financing in Oregon

I want to be blunt here, because this is the single most common wrong turn I see on ADU financing in Oregon.

A DSCR loan, short for debt service coverage ratio, qualifies a property on its rental income rather than your personal income. It is a business-purpose loan and it is non-owner-occupied by definition. You cannot live on the property. My guide to DSCR loans in Clackamas County walks through what the product actually does.

Now put that next to your project. You live in the main house. The ADU sits on the same tax lot as your residence. That property is owner-occupied, which means it is not DSCR-eligible, no matter how well the little unit would cash flow on its own. The good news is that you do not want a DSCR loan here anyway, because owner-occupied financing is the better deal on almost every term that matters.

And to say the obvious out loud: telling a lender you will not occupy a property you plan to live in, or the reverse, is occupancy misrepresentation. That is loan fraud, not a paperwork technicality. If the numbers only work by misstating occupancy, the numbers do not work.

Where DSCR does belong is a separate property you buy purely as a rental, and that is a different conversation with different down payment and reserve requirements.

Where an ADU Pencils Best in Clackamas County

Lot shape and rent demand matter as much as the loan does. A few local patterns worth knowing before you commit.

• Older, deeper lots. Neighborhoods with mid-century housing stock and generous back yards give you room for a detached unit without a variance fight. Ardenwald in Milwaukie is a good example, and its rental demand is steady.
• Inside Portland city limits. If your home is in Sellwood-Moreland or another Portland neighborhood, you get the full system development charge exemption and the covenant that comes with it. That is the biggest fee break available anywhere near this county.
• Garage conversions. Converting existing enclosed square footage is usually the cheapest path to a legal unit, and it fits the FHA renovation route cleanly because the work attaches to an existing structure.
• Long holds. An ADU is a slow instrument. It adds a rent stream and it adds value, but the fees, the permits, and the build cycle mean it rewards people who plan to stay put for a while.

If you want to see how the rest of the county's loan options fit together, my Clackamas County home loan programs hub is the place to start.

Frequently Asked Questions About ADU Financing in Oregon

Can I use a DSCR loan to build an ADU on my own property?

Can projected ADU rent help me qualify for the loan?

Can my city require me to live on the property to have an ADU?

What do system development charges cost on an ADU in Clackamas County?

Does taking the ADU fee waiver stop me from renting the unit nightly?

Can I do a cash-out refinance to build an ADU and use the future rent to qualify?