Investing in small multifamily: why duplexes to fourplexes are the sweet spot
2-4 unit properties get residential financing with commercial-grade income — the best risk-adjusted format in residential real estate, and the five-unit line where everything changes.
Why invest in small multifamily? Because 2–4 unit properties sit on the favorable side of the most important line in real estate finance: they qualify for residential mortgages — 30-year fixed, low rates, high leverage — while producing multiple rent checks like commercial property. A fourplex is four incomes on one roof, one loan, one insurance policy and one address, financed like a house. At five units, all of that changes at once.
The five-unit line
One extra unit rewrites your lending, insurance, and buyer pool:
| 2-4 units (residential) | 5+ units (commercial) | |
|---|---|---|
| Financing | 30-year fixed, Fannie/Freddie eligible, down to 3.5-5% owner-occupied | Commercial/agency loans: 5-10 year terms, balloons, 20-30% down |
| Qualification | Your income and credit (DTI), plus rents | The property's DSCR first, sponsor second |
| Valuation | Sales comps — what similar buildings sold for | Income approach — NOI ÷ cap rate; you can force value by raising NOI |
| Buyer pool at exit | Investors AND house hackers (deep, retail-priced) | Investors only (thinner, sharper-penciled) |
| Rate risk | None after closing — fixed for 30 years | Refinance roulette at every balloon |
Both sides of the line are good businesses — the Wealth pillar lives on the commercial side deliberately, because income-approach valuation lets operators force appreciation. But for an investor in Years 3–8, the residential side's 30-year fixed debt is a gift: permanent financing, no balloon, no refinance deadline a bad market can weaponize.
The per-door math
Four doors, two ways — four scattered $150k houses versus one $520k fourplex, same neighborhood quality, same $1,100 rents:
The fourplex wins on entry cost and operating efficiency; the houses win on liquidity and appreciation (single-family comps run hotter). That trade is worth making consciously — for the income-building years, efficiency usually wins.
What changes operationally
More doors on one address means landlording concentrates: same-building tenants share walls, parking, and grievances, so tenant screening and clear house rules do more work than in scattered rentals. Mechanical systems multiply (four water heaters, four kitchens) — the CapEx line in your underwriting is not decorative. And at four-plus doors, software and systems stop being optional: this is where the Operations section becomes load-bearing, and where hiring management (priced into your analysis from day one) starts earning its fee.
Buying them well
Small multifamily inventory is older and scarcer than houses — much of it built pre-1980, much of it held by the same landlord for decades. That's the opportunity: tired-landlord properties with below-market rents and deferred cosmetics are the classic value-add. Underwrite at current rents (the discount you negotiate lives there), plan the rent-to-market path unit by unit at turnover, and let the deal analyzer verify the deal clears DSCR 1.25 as it sits — not as it might become. If the as-is numbers only work at pro-forma rents, you're paying the seller for work you haven't done yet.
Frequently asked questions
+Is a duplex or fourplex a good investment?
For investors building rental income, 2-4 unit properties are arguably the best risk-adjusted format available: residential 30-year fixed financing, multiple rent checks diversifying vacancy, lower per-door costs than houses, and eligibility for house-hack entry at 3.5-5% down.
+What is the five-unit rule in real estate?
At 5+ units, a property crosses from residential to commercial lending: shorter loan terms with balloon payments, higher down payments, DSCR-driven qualification, and income-approach valuation (NOI ÷ cap rate) instead of sales comps. The line changes financing, risk, and how value is created.
+Is a fourplex better than four single-family rentals?
The fourplex is usually cheaper per door, cheaper to close, and more efficient to operate (one roof, one policy, one address); scattered houses appreciate faster and sell into a deeper market. For the income-building phase, most investors are better served by the fourplex; many later 1031 into either scale or quality.
+How are 2-4 unit properties valued?
By sales comparables, like houses — not by income like commercial property. This cuts both ways: you can sometimes buy strong income at homeowner-driven prices, but you also can't force appreciation just by raising rents the way 5+ unit owners can.
+How much down payment does a fourplex require?
As an investment: typically 25% conventional. As an owner-occupied house hack: 3.5% FHA (subject to the self-sufficiency test) or 5% conventional. That owner-occupied discount is the single cheapest entry into four-door ownership that exists.