A fourplex is residential property for almost every purpose that matters to an owner or buyer. Lenders, the IRS, and most zoning codes treat buildings with one to four dwelling units as residential, which is why the question of whether a fourplex is commercial or residential almost always comes out on the residential side. The main exception is insurance, where carriers typically shift to commercial-lines policies at four units. The classification can change depending on who is asking and why, so it helps to see how each system draws the line.
How Lenders Classify a Fourplex
The most consequential classification happens at the lending level. Fannie Mae and Freddie Mac, which back the vast majority of conventional mortgages in the United States, purchase or securitize mortgages “secured by residential properties when the dwelling consists of one to four units.”1Fannie Mae. Selling Guide – General Property Eligibility A building with five or more units crosses into commercial territory and requires a different loan product with different underwriting.
That bright line at four units is why fourplexes are so popular with small-scale investors and house-hackers. You get residential loan terms on what is, functionally, a small apartment building.
Conventional Loans
Under Fannie Mae’s April 2026 eligibility matrix, an owner-occupied fourplex qualifies for a maximum loan-to-value ratio of 95% through Desktop Underwriter, meaning 5% down. If the loan requires manual underwriting, the requirement jumps to 25% down for three- and four-unit properties.2Fannie Mae. Eligibility Matrix April 1, 2026 Repayment terms run up to 30 years, and rates track close to single-family residential rates with a pricing adjustment for multi-unit properties.
The 2026 conforming loan limit for a four-unit property is $1,601,750 in most of the country and up to $2,402,625 in designated high-cost areas.3Fannie Mae. Loan Limits If the same building had a fifth unit, the buyer would be in commercial lending territory: shorter repayment, higher rates, down payments of 20% to 30% or more, and underwriting focused on the property’s income rather than the borrower’s personal finances.
FHA and VA Loans
FHA-insured loans allow owner-occupants to buy a fourplex with as little as 3.5% down, but three- and four-unit properties must pass a self-sufficiency test: projected net rental income from all units, including the one you’ll live in, must cover the full monthly mortgage payment (principal, interest, taxes, insurance, and mortgage insurance premiums). The FHA counts net rental income as 75% of the appraiser’s estimated market rent, which builds in a 25% vacancy buffer. If the math doesn’t work at that discounted rent, the loan is declined.
Veterans and active-duty service members can use VA loan benefits to buy a fourplex with no down payment, as long as they occupy one of the units as a primary residence. The property cannot be held purely as an investment.
How the IRS Classifies a Fourplex
The IRS treats a fourplex as residential rental property, which puts it in a more favorable depreciation category than a commercial building.
Residential rental property is depreciated over 27.5 years under the Modified Accelerated Cost Recovery System. Nonresidential real property uses a 39-year schedule.4Office of the Law Revision Counsel. 26 U.S. Code 168 – Accelerated Cost Recovery System A fourplex owner deducts the building’s cost roughly 42% faster than the owner of a commercial building of similar value. On a $600,000 structure, excluding land, that works out to about $21,818 a year in depreciation for a fourplex versus about $15,385 for a commercial building. Real money shielded from tax each year.5Internal Revenue Service. Publication 946 – How to Depreciate Property
If you occupy one of the four units, only the rental portion of the building qualifies for depreciation. You’d depreciate roughly 75% of the building’s cost, allocated by relative square footage or fair market value rather than a flat unit count.
The residential classification carries through to sale as well. On an owner-occupied fourplex, the unit you lived in may qualify for the Section 121 capital gains exclusion (up to $250,000 single, $500,000 married filing jointly) if you occupied it as a primary residence for at least two of the five years before the sale. Gain on the rental portion is fully taxable, with depreciation recapture at 25%, and can be deferred through a 1031 like-kind exchange on the investment portion only.6Office of the Law Revision Counsel. 26 U.S. Code 1031 – Exchange of Real Property Held for Productive Use or Investment
How Zoning Classifies a Fourplex
Local zoning codes typically place fourplexes in residential districts, often in a multi-family residential category that permits buildings up to four units. The specific district label varies by city, but the pattern is consistent: fourplexes sit in residential zones, and five-plus-unit buildings often require commercial or higher-density residential zoning.
Watch for non-conforming use. If zoning rules change after a fourplex is built, the property may become legally non-conforming. It can continue operating, but it can’t expand, and rebuilding after major damage may be restricted. A grandfathered fourplex that suffers a fire may not be rebuildable as four units if current zoning no longer allows multi-family use. Before buying, check whether the current use conforms to today’s zoning code or relies on non-conforming status.
Where a Fourplex Is Treated as Commercial: Insurance
Insurance is the one area where the residential label falls away. A fourplex generally requires a commercial-lines insurance policy rather than a standard homeowner’s policy, even when the owner occupies one unit. Standard homeowner’s insurance is built for owner-occupied properties with one to three units. At four units, most insurers move you into a commercial dwelling or landlord policy that covers property damage, liability, and loss of rental income, with higher premiums and a different coverage structure.
Owner-occupants sometimes assume a homeowner’s policy will cover the building. It won’t, or at least not adequately, and a claim denied for the wrong policy type is one of the more expensive mistakes in small-scale real estate. Buy a policy designed for a four-unit rental, and confirm it covers fair rental value if a covered loss makes units uninhabitable.
Fair Housing and Landlord-Tenant Rules
Residential landlord-tenant law governs fourplexes in every state. Lease requirements, security deposit limits, notice periods, habitability standards, and eviction procedures apply the same way they would for any residential rental. Many cities also require landlords of multi-unit buildings to register the property and obtain a rental license, with annual per-unit fees that vary by locality. Failing to register can produce fines, and in some jurisdictions an unregistered property can’t pursue an eviction until it comes into compliance.
Federal fair housing law contains one wrinkle that happens to track the four-unit line. The Mrs. Murphy exemption at 42 U.S.C. ยง 3603(b)(2) exempts “rooms or units in dwellings containing living quarters occupied or intended to be occupied by no more than four families living independently of each other, if the owner actually maintains and occupies one of such living quarters as his residence.”7Office of the Law Revision Counsel. U.S. Code Title 42 – 3603 An owner-occupied fourplex sits at the edge of that threshold. The exemption is narrower than it looks: it doesn’t apply if a real estate agent or property manager is involved in finding tenants, it doesn’t override state and local fair housing laws, and it never permits discriminatory advertising. Most owners should comply with fair housing standards across the board.