You’ve got a duplex, or you’ve been looking at them, and the math feels thin. Two units, one vacancy, half your income gone.
So you look up. Triplexes. Fourplexes. Maybe someone calls it a quadplex. More doors, same roof.
Fourplex investing is one of my favorite places in the market. Here’s why, and what you need to understand before you step up.
Why three and four units
Vacancy hurts less
On a duplex, one empty unit is half the building. On a fourplex, it’s a quarter. That doesn’t promise anything, but it’s a real difference in how a bad month feels.
Management gets more efficient
Four units at one address means one trip, one roof, one yard, one set of grounds to keep up. When I’m running maintenance, clustering doors is how I keep the work sane. The same systems run one unit or four at an address; that’s the leverage.
It’s still residential
Here’s the big one. In US lending, one to four units is generally treated as residential real estate. Five or more is usually commercial. A fourplex is the biggest building you can typically finance with residential loan products.
That matters because residential and commercial lending are different worlds.
1–4 unit residential vs. 5+ commercial financing
I’m not a lender, and programs change, so treat this as a map, not a quote. Talk to a lender for real terms.
| 1–4 units (residential) | 5+ units (commercial) | |
|---|---|---|
| Typical loan types | Owner-occupant programs, conventional investment loans, DSCR loans | Commercial bank loans, agency and other commercial programs |
| How it’s valued | Often leans on comparable sales, like a house | Leans heavily on income and cap rate |
| What the lender focuses on | Your credit and reserves, plus the property’s rent | The property’s operating history and income, plus your experience |
| Owner-occupancy | Often allowed if you live in a unit | Generally an investment loan |
| Terms | Long amortizations are common | Shorter terms and balloons are more common |
The valuation row is the part people miss. On a fourplex, the appraiser usually leans on what similar fourplexes nearby sold for. Raising rents can help, but comps still anchor value. On a large apartment building, income drives value much more directly.
Some investors find comps for triplexes and fourplexes are thin in smaller towns. That can make appraisals tricky. Learn how I approach it on the comps guide.
Owner-occupant fourplexes
Many owner-occupant loan programs allow up to four units if you genuinely live in one. That makes a fourplex house hack possible. But three- and four-unit owner-occupant loans can come with stricter requirements on reserves and on how much of the other units’ rent the lender will count. Some also require the property to pass a self-sufficiency test of its own. Ask your lender specifically. Never claim occupancy you don’t intend.
More on the owner-occupant path on the house hacking page.
How I underwrite a triplex investment
Same discipline as everything else I buy to hold.
- Rent each unit separately on its own comps.
- Screen with the 1% rule against all-in cost: monthly rent across all units at least 1% of purchase plus repairs plus closing.
- Check the price against roughly the 70% rule, using fourplex comps for the after-repair value and a real bid for the work.
- Build the full operating budget, including owner-paid utilities, which are common on older multi-unit buildings.
- Calculate NOI, cash flow, cap rate and cash-on-cash using the NOI, cap rate and cash-on-cash formulas I lay out for rentals.
- Stress test two vacancies at once plus a major shared-system repair.
What gets harder at three and four units
Shared systems concentrate risk. One main sewer line, one roof, sometimes one boiler or water heater for several units. When it goes, everyone calls you the same day.
Utility billing. Older buildings may have one water meter for all units. That’s an owner expense unless your lease and local rules allow a different arrangement.
Turnover volume. More units means more move-outs, more turns, more leasing. Your system has to handle it without you being the bottleneck.
Life safety and code. Fire separation, egress, smoke and CO detection. Confirm the building meets current requirements for its use.
Tenant mix. Four households sharing walls, parking and a yard. Clear rules in the lease, applied consistently and fairly, save a lot of conflict.
Managing a fourplex
At this size, I want a real system, whether I self-manage or hire a manager.
- One intake channel for maintenance requests.
- A vendor bench for every trade.
- A rent collection process with clear follow-up steps.
- A renewal calendar so leases don’t all expire in the same month.
- A weekly scorecard: vacancy, delinquency, open work orders.
That’s the kind of thing I built REI Boss to run. Whether to run it yourself or hand it off is its own decision; I break it down on my property management page for investors.
Where I buy them
My rental buy box is small multifamily within about an hour of the Midlands. I’ve worked a small multifamily renovation in Greenwood and I hold rentals in Newberry and Lancaster County. If you own a triplex or fourplex in that footprint, owners, licensed agents and investors who own the property can see what I buy in South Carolina. If you’re researching the Midlands as an investor, start with my Lexington SC rental guide or the Sumter rental market breakdown.
Your next step
Before you write an offer on your first triplex or fourplex, share it with the investors inside REI Skool, which costs nothing to join. Rent every unit on its own comps, list the shared systems and their ages, and let other investors check your work. If you’re still deciding between building sizes, start with the small multifamily investing overview, or compare with how to buy a duplex.
Questions people ask
Is a fourplex residential or commercial?
In US lending, a property with one to four units is generally financed as residential. Five or more units usually moves into commercial lending. Local zoning and insurance may classify things differently, so confirm with your lender, insurer and zoning office.
Is a fourplex a good investment?
It can be, if it’s bought at a real discount, every unit is underwritten on its own comps, and the building’s systems are understood. Four rent checks under one roof spread vacancy risk, but shared systems concentrate repair risk. The purchase price decides more than the unit count.
Can I live in a fourplex and rent the other units?
Many owner-occupant loan programs allow up to four units if you truly live in one. Requirements for reserves and how rental income is counted can be stricter on three and four units than on a duplex. Talk to a lender before you shop.