Multi-Unit BRRRR Underwriting — What Changes from 1 Unit to 4

What stays the same

Before we get into what changes, an honest note on what doesn't. The core BRRRR question — can I buy + rehab + hold for less than 75% of ARV, refinance, and recycle my capital? — is the same on a single-family and a four-plex. Hard money cost structure is the same: points up front, monthly interest on the outstanding balance, rehab draws on a schedule. Holding cost math is the same — taxes, insurance, utilities, multiplied by months of carry. Refi closing costs ($3k–$5k) hit either deal type the same way.

So if you can underwrite an SFR BRRRR cleanly, you already have the engine. Multi-unit just changes seven inputs into that engine — and changes them all in ways that compound if you miss them.

1. Vacancy variance smooths out

On a single-family, vacancy isn't a percentage — it's a binary. The unit is rented or it isn't. When it's empty, you're carrying 100% of the mortgage with 0% of the income. Stretch one bad turnover into two months of vacancy and you've wiped out a quarter of the year's cash flow.

On a 4-unit, one empty unit is 25% vacancy. You're still carrying the full mortgage, but three units are paying it down. The Law of Large Numbers kicks in even at four doors — your 5% vacancy assumption actually starts behaving like 5% over a year instead of swinging from 0% to 100% month to month.

How to underwrite it: on an SFR, I run 8–10% vacancy regardless of what the market average is, because the variance is real and one bad month destroys an annual underwrite. On a 4-unit, I run 5–6%. The average is similar; the standard deviation is dramatically lower.

2. Operating expenses don't scale linearly

The lazy underwrite multiplies SFR expense ratios by four to get a quad expense. That's wrong in both directions on different line items.

Property tax scales linearly with the assessed value. Nothing clever to do here. Insuranceon a single 4-plex policy is frequently cheaper per door than four separate landlord policies on four separate SFRs — one roof, one structure, one liability policy. Run a quote, don't assume.

Maintenance and CapEx reserves drop per door on a multifamily because the big-ticket items are shared. One roof for four units instead of four roofs. One exterior to paint. Shared mechanicals in some configurations. I run 5%/5% maintenance and CapEx on an SFR and closer to 4%/4% on a tight 4-unit — same percentage of gross rent, but gross rent on the quad is 3–3.5× the SFR, so the dollar reserve is healthier per dollar of shared infrastructure.

Management is usually cheaper per door on a multifamily because the PM has one set of trips, one set of leases at one address, and one set of bills to handle. Standard pricing in OKC drops 1–2 points when you scale into 4+ units under one roof. Real number, not folklore.

3. Refi math gets stricter — welcome to DSCR

This is the single biggest underwriting difference, and it's where I see operators get caught flat. SFR refis underwrite primarily on personal income or DSCR with the borrower's W-2 as a backstop. Banks lean on the borrower more than the property.

4-unit refis underwrite the property. DSCR — debt service coverage ratio — is NOI ÷ annual debt service. Banks want 1.20–1.25 minimum. A 1.20 DSCR means NOI is 20% higher than the mortgage payment. Below that floor, the refi doesn't close. Full stop. Doesn't matter how much income you have, doesn't matter how good your credit is.

Worked example. 4-unit with $5,800/mo gross rent ($1,450 average per door, OKC small multifamily range). 5% vacancy = $5,510 effective gross. Operating expenses: taxes $450, insurance $180, management $385 (7% on a quad), maintenance $230 (4% gross), CapEx $230, utilities (common areas) $95. Expenses = $1,570. NOI = $3,940/mo or $47,280/year.

Refi loan of $260,000 at 7.5% on a 30-year amortization = $1,818/mo P&I, or $21,816/year debt service. DSCR = 47,280 ÷ 21,816 = 2.17. Fine — that refi closes easily.

Now rerun the same deal with ambitious rents that didn't materialize. $5,200/mo actual gross instead of $5,800. Suddenly NOI drops to ~$41,400, DSCR drops to 1.90. Still fine. Stretch the loan to $320k at the same rate ($26,800/year debt service) and DSCR is 1.54. Still fine. Push to 8.5% and a $320k loan and now you're at 1.40. Margin's getting thin. The point: model DSCR explicitly on every multifamily underwrite at the rents the market will actually pay, not the rents you hope for. If you're below 1.30 in the underwrite, you're betting the refi closes on perfect inputs — and refis don't close on perfect inputs.

4. ARV is harder to underwrite

SFR ARV is comp-based. Pull three to five recently sold homes in the same submarket, adjust for square footage and condition, average them. The data's thick. The appraiser is going to land within ~3% of a tight comp set most of the time.

4-unit ARV is income-based. The appraiser estimates NOI, picks a market cap rate, and divides. Cap rate is opinion. Two appraisers in the same market on the same week can disagree by 50–100 basis points on the cap rate they apply. On a property doing $47k NOI, the difference between a 7.5% cap and an 8.5% cap is $74,000 of ARV — gone, on opinion. (How to read the report and decide what to push back on lives in reading an appraisal as an investor.)

How to underwrite: assume the appraiser uses a cap rate 50–100 basis points higherthan your acquisition cap. If you're buying at a 7.5% cap, underwrite ARV using an 8.25–8.5% cap. If the deal still pencils, you have appraisal protection. If the deal only works at the cap rate you bought at, you have no margin for an appraiser who reads the market a half-point differently than you do.

5. Rehab gets more complex, not just bigger

The naive math: 4-unit rehab = 4 × SFR rehab. Wrong on both directions. Wrong cheap (you're sharing exterior, mechanicals, roof) and wrong expensive (common areas, hallways, mechanical rooms, parking, exterior staircases on stacked plans — none of which exist on an SFR).

The harder problem is tenant-in-place rehab. On a vacant 4-unit, you scope the whole building and the GC sequences it. On a 4-unit with two tenants in place, you can't gut renovate units 3 and 4 the same way — noise, dust, water shutoffs, sequencing around human beings who pay you rent. You either rehab the vacant units now and the occupied units at turnover (12–24 month timeline), or you offer cash for keys and risk vacancy spiking right when you need DSCR to perform for the refi.

Bottom line: a 4-unit rehab almost always costs more total dollars AND takes more calendar time than 4× a comparable SFR rehab. Underwrite extra holding months. Underwrite tenant-in-place inefficiency. If your spreadsheet has 4 units rehabbing in the same six months as a single SFR, the spreadsheet is lying to you.

6. Tenant screening becomes a bigger lever

Counterintuitive answer: tenant screening matters more on a multifamily, not less. The arithmetic says less — one bad tenant on a 4-unit is 25% of your income at risk, versus 100% on an SFR. So screening should be less critical, right?

No — because of contagion. A bad tenant in an SFR damages the property. A bad tenant in a 4-unit damages the property AND drives out the good tenants you already have. Noise, parking conflicts, smell, police visits — these things compound when units share walls and parking. A 4-unit that loses two of its three good tenants to one bad placement is an asset with 50% real-world vacancy on a building that's only listed as 25% empty.

How to operationalize: tighten income multiple (3.5× rent minimum), tighten credit floor (640+), explicit ban on prior evictions, in-person walk-through of current residence before approval. The screening process that's overkill on an SFR is appropriate on a multifamily.

7. Financing options expand — but get pickier

SFR financing menu: conventional 30-year, DSCR loan, portfolio lender, private lender, hard money to refi to permanent. Decent menu, mostly priced within 50 basis points of each other for similar credit profiles.

4-unit financing menu: same menu plus the option to step up into commercial multifamily loans (typically 5+ units, but some lenders bracket 4 as small commercial). Commercial loans price differently — 5/10/15-year fixed rates, longer amortization sometimes, balloon payments, prepayment penalties, occasional recourse vs. non-recourse splits. The spread between products on a 4-unit can be 75–100 basis points for the same credit, same property, same rent roll.

That means shopping matters more. Three SFR lenders gets you a sense of the market. Six multifamily lenders gets you a sense of the market — and the cheapest quote will usually come from a regional bank or credit union that doesn't show up on aggregator sites. Build the relationship before you need the loan; commercial underwriting is relationship business in a way SFR refi isn't.

8. Property management economics flip

On a single SFR, self-managing pencils. Your time is cheap relative to an 8–10% management fee. One tenant, one lease, one call a quarter — totally manageable in two hours a month.

On a 4-unit, self-managing still works, but the math is shifting. Four leases, four renewals, four turnovers on staggered timelines, four sets of maintenance calls. By the time you have three 4-units (twelve doors), you're unconsciously absorbing a part-time job and pretending it's passive.

Underwrite professional management from day oneon multifamily, even if you're planning to self-manage initially. If the deal only works because you're free, the deal doesn't actually work. Build the 7–8% management line into the proforma. If it still pencils, you have an asset that will scale with you. If it doesn't pencil with management, you're buying yourself a job, not a business.

Side-by-side — SFR vs. quad, similar $/door

Two illustrative BRRRRs in the same OKC submarket, comparable per-door all-in cost, very different refi outcomes.

SFR.All-in $172,000 on a $235,000 ARV. Refi at 75% LTV = $176,250. Refi costs $4k. Net cash back: roughly flat. Rent $1,750. P&I/taxes/insurance/management/reserves out: ~$324/mo cash flow. Annual NOI ~$15,800. Debt service ~$15,780. DSCR right at 1.00 — fine on an SFR refi qualified by borrower income, would be unfinanceable as a pure DSCR product.

Quad, same per-door basis. All-in ~$688,000 (4 × $172k). ARV via income approach: NOI $47,280, applied cap rate 8%, ARV = $591,000. That's the cap rate trap.Even though per-door rehab and basis line up with the SFR, the appraiser's cap-rate-driven ARV doesn't. Refi at 75% of $591k = $443,250. You're leaving ~$245,000 stuckin the deal, even though you'd underwrite an identical SFR as a near-full BRRRR.

The takeaway: per-door cost analysis is useful but lies on multifamily. The refi check is governed by income × cap rate, not by your per-door basis. Multifamily BRRRRs require you to underwrite to the cap rate the appraiser will use, with the rent the market will actually pay, and then verify DSCR clears at the loan amount that recovers your capital. Three constraints, not one.

The honest summary

Multi-unit BRRRR is the same strategy as single-family BRRRR with a different risk profile. You trade vacancy variance for cap rate variance. You trade tenant turnover risk for tenant contagion risk. You trade simple comp-based ARV for opinion-based ARV that depends on the appraiser's cap rate. You gain economies of scale on expenses and management; you lose flexibility on rehab sequencing and refi qualifying.

The operators who scale into small multifamily successfully are the ones who model DSCR from day one, underwrite ARV with a punitive cap rate, and budget for tenant-in-place rehab inefficiency. The operators who get hurt are the ones who treated a quad like 4× an SFR on a per-door basis and assumed the refi math would behave the same way.

Run your next multi-unit BRRRR with all four constraints — basis, DSCR, cap-rate-driven ARV, and rehab timeline — and the path from one unit to four becomes a math exercise instead of a learning experience.