House Hacking in San Diego: A General Look at Duplexes and ADUs

by Trevor Landress

House hacking means buying a home, living in part of it and renting out another part. At the time this article was written (October 2026), the Federal Housing Finance Agency listed 2026 loan limits for San Diego County of $1,104,000 for a one-unit home, $1,413,350 for two units, $1,708,400 for three units and $2,123,100 for four units. Those limits matter because they decide whether a loan is treated as a conforming loan. This guide is a general overview. It is not lending, tax or legal advice, and I am a REALTOR, not a lender.

The short answer

House hacking means living in one unit and renting out another, such as the other side of a duplex or an ADU.
At the time this article was written, FHFA listed 2026 conforming loan limits for San Diego County of $1,104,000 for one unit and $1,413,350 for two units.
Fannie Mae's guide describes how a lender may count rent from the property, including using 75% of gross rent in one method.
Every lender and loan program has its own rules, so the lender decides what counts.
This is general information only. Please talk with a lender, a CPA and an attorney about your own situation.

What house hacking means

House hacking is a nickname, not a legal or lending term. It describes a buyer who lives in a property and rents out part of it, so the rent helps with the monthly cost. Common versions are a duplex, a triplex or fourplex, or a single home with an ADU or a rented room.

The buyer is also a landlord. That brings other topics with it, such as lease terms, the state rent cap and tax rules. I cover some of those in my overviews of rent increase rules in San Diego and cash flow.

Loan limits for 2 to 4 units in San Diego County

At the time this article was written, the FHFA's county list for 2026 showed these conforming loan limits for San Diego County. The national baseline for a one-unit home was $832,750. San Diego County is a higher-cost area, so its limits are higher.

Number of units	2026 loan limit, San Diego County
One unit	$1,104,000
Two units	$1,413,350
Three units	$1,708,400
Four units	$2,123,100

A loan above the limit is generally called a jumbo loan, and lenders may have different rules for it. The limits apply to the loan amount, not the price. The FHFA sets new limits each year, so the numbers above may change.

A made-up duplex example (my math)

This example is invented to show the steps. It is not an offer, a quote or a prediction.

Price of a duplex: $1,300,000 (invented). Down payment of 10%: $130,000. Loan: $1,170,000.
That loan is under the two-unit limit of $1,413,350. The same loan would be over the one-unit limit of $1,104,000.
Payment at an invented 6.5% rate for 30 years: about $7,395 a month for principal and interest.
Property tax at the 1% base rate: about $1,083 a month. Insurance (invented): $250 a month. Total, my math: about $8,729 a month.

Say the other unit rents for $2,246 a month, which is the county median rent from the Census, used here only as a stand-in. My math then shows two views.

View	Monthly housing cost left after rent
Counting all of the rent	$6,483
Counting 75% of the rent ($1,684)	$7,044

Before any repairs, empty months or other costs, that is only a rough picture. Real rent can be higher or lower, and the first view assumes that the unit is always rented. The 1% tax figure is a base rate, and a real bill can include extra charges. Please ask the County about a real bill.

How Fannie Mae describes rental income

At the time this article was written, Fannie Mae's Selling Guide (the 09/02/2026 edition, section B3-3.8-02) described how lenders can count rent from the subject property. It is a guide for lenders, so a lender may follow it, add to it or use a different program.

One method uses 75% of gross monthly rent, then subtracts the full monthly payment for principal, interest, taxes, insurance and association dues. Fannie Mae calls that payment PITIA.
The guide says 2 to 4 unit properties that are a principal residence are eligible.
The guide describes rent forms an appraiser fills out, Forms 1007 and 1025.
The guide describes how a borrower's experience as a landlord can change how positive rental income is counted. In one case, with less than 12 months of experience, positive income can only offset the payment.

I am not a lender, and I am only summarizing a public page. A lender can tell you what applies to a certain loan.

The ADU path

A buyer can also look at a single home that already has an ADU. For a one-unit property, Fannie Mae's guide described a limit on counting ADU rent. It said only one existing ADU counts, and the rent counted is capped at 30% of the borrower's qualifying income.

The City's rules for ADUs are a separate topic. My overviews of ADUs in San Diego and junior ADUs vs. detached ADUs go through the City's published rules and cost ranges. Short-term stays are limited in the City.

Other points people raise

A buyer who lives in the property and rents the rest can have other questions. Some are about how long the buyer must live there, how the loan treats the rent and what happens if a unit sits empty. Others are about taxes. A lender, a CPA and an attorney can each answer their part.

As a REALTOR, I can help with the market side, such as looking at properties, comparing prices and negotiating an offer. My guide on how much income you need to buy in San Diego covers the basic affordability side.

Please talk with a professional

Loan limits change each year, lender rules differ, and the example above uses invented numbers. A mistake in a rental income calculation could change a loan decision.

I am a REALTOR, not a lender, CPA or attorney. Please talk with a lender about financing, a CPA or tax professional about taxes, and an attorney about leases and landlord duties.

Questions people bring to a lender or professional

Which loan programs allow 2 to 4 unit homes, and what are the down payment rules?
How will the lender count rent from the other unit or the ADU?
What is the loan limit for the number of units in this county this year?
How long must I live in the property under the loan terms?
What landlord duties, taxes and insurance changes come with renting a unit?

Call or text me at (619) 402-4614 or send me a message.

Call or text (619) 402-4614 Contact Trevor Landress

Related guides

Frequently asked questions

What is house hacking?

It is a nickname for buying a home, living in part of it and renting another part, such as the other side of a duplex or an ADU. It is not a lending or legal term.

What is the conforming loan limit for a duplex in San Diego County?

At the time this article was written, the FHFA listed a 2026 limit of $1,413,350 for a two-unit property in San Diego County. Limits change each year, and a lender can confirm the current one.

Can rental income help me qualify for a loan?

At the time this article was written, Fannie Mae's Selling Guide described ways lenders may count rent from the property, including using 75% of gross rent in one method. Each lender decides what it will count.

Can I count ADU rent when I apply for a loan?

At the time this article was written, Fannie Mae's guide said only one existing ADU counts for a one-unit property, with the rent capped at 30% of qualifying income. Please ask a lender about your loan.

Do I have to live in a duplex I buy with an owner-occupied loan?

Loan terms for a principal residence usually involve living in the home. The details depend on the loan, so please ask a lender and an attorney about the exact terms.

About the author

Trevor Landress is a San Diego REALTOR® with Coldwell Banker West (DRE# 02126901). He was born and raised in San Diego and has been licensed since 2021. Trevor helps homeowners sell, guides first-time buyers through the home buying process and assists investors with their next acquisition. His work includes negotiating offers, analyzing market trends, building pricing strategies and running marketing campaigns for his listings.

He serves clients across San Diego County, from coastal communities like La Jolla, Del Mar and Carlsbad to neighborhoods inland. Trevor is part of the Campbell Group, a three-generation real estate team, and he and the Campbell Group consistently rank as a top producing team at Coldwell Banker West each month. He writes these guides to help San Diego buyers and sellers navigate an ever-changing market.

Each guide on this blog is built from official or primary sources, and the text names the source and the month it was checked. When a fact can go stale, such as a rate, a fee, a deadline or a rule, the guide says so. The goal is plain answers you can use before you make a big decision.

Trevor is a REALTOR, not a tax advisor, attorney, lender or contractor. For questions in those areas, he recommends you check with the right professional. To talk through your plans, call or text (619) 402-4614 or contact Trevor Landress.

How I help San Diego home buyers

Trevor guides first-time buyers through the home buying process, from setting a budget to closing. His work includes negotiating offers and analyzing market trends so buyers understand what a home may really cost to own.

How I help San Diego home sellers

Trevor helps homeowners sell with pricing strategies, marketing campaigns, offer negotiation and market analysis, so sellers know what to expect before they list.

Sources

This guide is general information only. It is not tax, legal or financial advice, and I am not a tax professional or an attorney. Please talk with a licensed CPA, tax professional or attorney, and with the County or the agency named above, before you make any decision.