How people pay for a backyard home

Most backyard homes are paid for in one of four ways, and many projects mix two. Which one fits depends on three questions: how much equity you have today, whether you want to keep the mortgage you already have, and whether you would rather borrow against what the property is worth now or what it will be worth when the home is finished.

We do not lend or broker loans. This is how the options work, so the conversation with a lender goes faster; a lender, and your tax advisor, decide which one fits you.

Savings

The simplest route: no loan, no lender inspections, and payments come out of savings at each milestone. Builders publish a contingency of 10 to 20 percent for what the ground or an old house turns up, and savings are the easiest place to hold it. Some people pay for design and engineering from savings and borrow only for construction.

A home equity line of credit

A home equity line of credit, or HELOC, lets you borrow against your equity, the home’s value minus what you owe, up to a limit the lender sets. It sits behind your first mortgage, so the mortgage and the rate you have stay as they are.

It suits a build because you draw money as each milestone comes due and pay interest only on what you have drawn. Two things to understand before you sign. HELOCs usually carry a variable rate, so the payment can change. And they have two phases: a draw period (the Consumer Financial Protection Bureau gives ten years as an example) when you can borrow, then a repayment period when you can’t, and the payment can be much higher. The line is secured by your home.

It fits when you have substantial equity and want to keep your first mortgage.

A renovation or construction loan

When the equity you have today isn’t enough, these loans lend against what the property is expected to be worth when the home is finished, the “as-completed” value, based on the plans, a budget and a signed contract. The money is released in draws, usually after the lender’s own inspection of each milestone. That paperwork is why the loan comes after design: the lender needs the drawings and the fixed price.

The three national programs are first mortgages, so they replace the one you have:

• Fannie Mae HomeStyle Renovation (purchase or refinance). Renovation costs can reach 75 percent of the as-completed value on a refinance, the work has to be finished within 15 months, and Fannie Mae’s guidance allows the accessory unit to be detached if it meets state and local code. A December 2025 update lets lenders release up to half of the renovation cost at closing, for materials and permits.
• Freddie Mac CHOICERenovation (purchase or refinance) can add a new ADU or renovate an existing one.
• FHA 203(k): since October 2023, a 203(k) can add an ADU attached to the existing home, convert part of the home into one, or renovate an existing ADU.

Many banks and credit unions also offer their own construction loans or renovation lines, and some of those sit behind your first mortgage instead of replacing it. Ask.

It fits when most of the project’s value is in the finished home rather than in your equity today.

A cash-out refinance

A new, larger mortgage replaces the one you have, and the difference is paid to you at closing. The money arrives as one lump sum before the build, and you pay interest on all of it from the first day.

The catch is in the word replaces: a cash-out refinance replaces your rate. If the rate you hold is lower than today’s, that is usually the thing you were trying to protect. It fits when your rate is already close to today’s, or you were going to refinance anyway.

Can the future rent help you qualify?

Sometimes, and the rules got friendlier recently. All three agencies now let lenders count rent from an accessory unit in some cases:

• Fannie Mae (October 2025): rent from one ADU can count toward your qualifying income, up to 30 percent of it, on a one-unit home you live in, for a purchase or a limited cash-out refinance.
• FHA (October 2023): on a purchase or a rate-and-term refinance, a lender can count 75 percent of the unit’s market rent (50 percent with a 203(k)), capped at 30 percent of your qualifying income, with two months of payments in reserve. Not on a cash-out refinance.
• Freddie Mac counts ADU rent toward qualifying when the requirements in its guide are met.

Lenders apply these with their own rules on top. The question to ask is whether they will count rent from a unit that isn’t built yet, and at what share.

How the payments line up with the build

However you pay, the money moves at milestones: the contract, the foundation, the weather-tight frame, the rough-in inspections, the drywall and the final inspection. A lender’s draw schedule follows the same rhythm, which is why a home equity line and a construction loan both fit a build better than a lump sum does. How a backyard home gets built walks through the stages behind each payment.

Questions to ask a lender

• Will you finance a detached backyard home, or only an attached unit?
• Do you lend on today’s value or on the as-completed value?
• Does this loan replace my first mortgage, or sit behind it?
• Is the rate fixed or variable, and what happens when the draw period ends?
• How are draws released: how many inspections, and how fast after we ask?
• Will you count future rent toward qualifying? At what share?
• What do you need from the builder, and when?

What the builder can give your lender

The fixed-price proposal, the plans and engineering, the payment schedule, the construction schedule, and United Signature’s contractor registration and insurance. Most of a lender’s file comes out of the design stage, which is one more reason to start with what fits on the lot. Send the address for the free report.