The five-unit line: where residential ends and commercial begins
At four units, the property is valued by comps and financed like a house. At five, it's valued by NOI, financed by DSCR, and insured like a business. Everything that changes at the line — and how to use it in both directions.
What changes at five units? Everything except the tenants. One-to-four-unit properties are residential: eligible for conventional and FHA financing on 30-year fixed terms, valued by comparable sales, bought and sold through the MLS. At five units and up, the same brick becomes commercial: valued by NOI and cap rate, financed by community banks and agency lenders on shorter terms with balloons, appraised by the income approach, and traded through brokers off pro formas. The line is arbitrary — Fannie Mae and Freddie Mac simply cap their single-family programs at four units — but the two worlds it separates run on different physics, and the investors who understand both directions of the line get paid twice: once for crossing it deliberately, and once for buying just under it from sellers pricing the wrong side.
Two valuation physics
Below the line, a fourplex in a neighborhood of $400k fourplexes is worth about $400k however brilliantly you operate it — comps are gravity, and forced appreciation means renovating toward what comparable properties sold for. Above the line, the appraiser opens the income approach and your operations are the value: raise rents $75/unit across ten units and you've created ~$9,000 of NOI — roughly $150,000 of appraised value at a 6 cap, conjured from paint, management, and nerve. This is the entire engine of the value-add playbook, and it's why serious operators eventually cross the line: below it you buy appreciation, above it you manufacture it.
| 1–4 units (residential) | 5+ units (commercial) | |
|---|---|---|
| Valuation | Comparable sales — the neighbors set your ceiling | NOI ÷ cap rate — your operations set the price |
| Financing | 30-yr fixed, 3.5–25% down, no balloon, non-recourse to your other assets by structure | Community bank/agency: 20–25 yr amortization, 5–10 yr balloon, 25–30% down, often personal recourse |
| Rate risk | None after closing — fixed for the hold | Repricing at every balloon — the 2023–24 lesson in one line |
| Appraisal | Sales comparison; renovations valued by comps | Income approach; the T12 and rent roll are the appraisal |
| Insurance | Landlord (dwelling fire) policy | Commercial package + loss-of-rents; underwritten on the schedule |
| Buyer pool at exit | Investors AND house hackers — deep, retail, financed | Investors only — thinner, slower, negotiated on your books |
| Records that matter | Your tax returns and W-2 | The property's books — provable NOI is literally the price |
The debt is the real difference
Residential debt is the anomaly of world finance: 30 years, fixed, no balloon, no covenants, sized partly on your W-2. Commercial debt is normal banking — DSCR-driven sizing (typically ≥1.20–1.25), 20–25 year amortization, and a balloon in year 5–10 that forces a refinance or sale at whatever the credit market looks like then. That maturity is the risk residential investors have never met: operators with performing properties faced 2023–24 balloons into 7%+ money and frozen lenders, and some lost buildings whose tenants never missed a month. Crossing the line means adopting maturity-ladder discipline — no balloon inside a plausible credit winter, refinance conversations starting 18 months early — as a permanent operating habit. Agency small-balance programs (Fannie/Freddie, roughly $1M+) restore longer fixed periods and non-recourse at the cost of paperwork; under ~$1M, community banks are the market, and the relationship is the product.
Playing both sides of the line
Under it, deliberately: the 2–4 unit band is the best risk-adjusted entry in real estate — duplex-to-fourplex doors on government-grade debt, house-hackable at 3.5% down, forgiving of amateur operations. A fourplex is four doors of income on a residential mortgage; a fifth door would cost you the mortgage. That trade is rarely worth it early.
Crossing it, on purpose: move when you have provable operating history, books a commercial appraiser can price, reserves sized for balloon risk — and a value-add thesis, because the income approach is the reward that justifies the harsher debt. The 5–20 unit band is the classic first crossing: below institutional radar, above homebuyer competition, full of tired-owner sellers with under-market rents — and small enough that one investor with a community bank can close it.
Arbitraging it: the line creates permanent mispricings. Fourplexes priced on gross rent by commercial-minded sellers get bought at comp discounts; 5–8 unit properties listed by residential agents with no T12 sell below income value to whoever reconstructs the books; and the fourplex buyer pool (investors plus FHA house hackers) reliably pays more per door than the six-unit buyer pool next block over — worth remembering on the way out, too.
Frequently asked questions
+Why are 5+ unit properties considered commercial?
Because the government-backed residential mortgage system (Fannie Mae, Freddie Mac, FHA) caps its programs at four units. At five, financing shifts to commercial credit — bank and agency multifamily loans — and valuation, appraisal, insurance, and sales process all reorganize around income rather than comparable sales. The line is regulatory, not architectural, but its consequences are total.
+Is it better to buy a fourplex or a five-unit building?
For most early investors, the fourplex wins decisively: 30-year fixed government-backed debt (down to 3.5% down if house hacking), no balloon risk, a deeper buyer pool at exit, and forgiveness for amateur operations. The five-unit's advantage — value forced through NOI — only pays once you have the operating skill and books to actually move NOI. Cross the line for a value-add thesis, not for one more door.
+How are commercial multifamily loans different from residential?
Sized by the property's debt-service coverage (typically ≥1.20–1.25 DSCR) rather than your income; 20–25 year amortizations with 5–10 year balloons instead of 30-year fixed; 25–30% down; often personal recourse at small scale; and rates repricing at every maturity. The balloon is the defining risk — a performing property can still face a hostile credit market at refinance.
+How is a 5+ unit building appraised?
Primarily by the income approach: the appraiser reconstructs NOI from the trailing-twelve financials and rent roll, applies a market cap rate from comparable sales of similar buildings, and derives value as NOI ÷ cap rate. Your books effectively are the appraisal — which is why provable, per-property accounting adds real dollars at refinance and sale.
+What is the best size multifamily to buy first?
The standard arc: 2–4 units first (residential debt, house-hackable, forgiving), then a 5–20 unit crossing once you have operating history and a value-add thesis. The 5–20 band is multifamily's classic sweet spot — too small for institutional buyers, too commercial for retail ones — offering the thinnest competition and the fattest mispricings, at a scale one investor and a community bank can still close.
The band below the line: duplex to fourplex investing. The reward above it: the value-add playbook. The debt ladder that spans both: the financing ladder.