Same House, Four Answers

One property, one conversion, four completely different deals

Four people stand in the same driveway looking at the same house. Four bedrooms, two stories, one bedroom and a full bath downstairs, three up. Detached two-car garage. Deep lot. It's worth $950,000 and it rents for $4,000 a month.

All four of them see the same thing: a junior unit carved out of the downstairs bedroom, the garage converted to a two-bedroom, three units where there was one. Call it $230,000 of work and $7,800 a month when it's done.

Same house. Same plan. Same rents.

Four different deals, and two of them are barely related to each other.

A note on the numbers. Everything here is illustrative. Prices, rents, rates, and especially construction costs vary widely. Get bids from licensed, insured, bonded contractors and verify licenses with the Contractors State License Board. Then substitute your own figures.

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Buyer One: The owner with a low-rate first

She bought in 2019. Assessed value around $400,000, and a 4% mortgage with roughly $600,000 still on it.

What she has that nobody else does: two protections at once.

Proposition 13 means converting reassesses the new construction only. Her original assessed value doesn't move. Property taxes go from about $4,200 to $6,600 — while a buyer of the same house pays roughly $12,400 from day one.

And she has a 4% loan in a 6.75% market. That's not a nice feature. It's an asset with a dollar value.

The mistake that would cost her the deal: refinancing to fund the construction.

A 203(k) or HomeStyle refinance would roll the conversion into a new first mortgage against after-improved value. It's a clean product and it would be a disaster here. Moving $600,000 from 4% to 6.75% costs roughly $1,100 a month — about $13,000 a year, for as long as she owns it.

The conversion generates roughly $23,800 in additional annual net operating income. Refinancing to pay for it would consume more than half of that, permanently. She'd pay for the conversion twice, once in construction and once in rate.

Her rule is simple: never touch the first. Construction money comes from cash or from second position. A home equity loan, a HELOC, an FHA Title I Property Improvement Loan — which is government-insured, sits in second or subordinate position, and exists specifically for owners who need improvement money without disturbing what they've got. Or a renovation second underwritten on after-renovation value.

What she gets: the best cash flow of anyone here. Net operating income moves from about $32,200 to about $56,000. Roughly a 10.3% return on the $230,000 she puts in, against a market paying 5.4% for stabilized product.

What she doesn't get: much depreciation. If the house was her residence, depreciable basis is the lesser of adjusted basis or fair market value at conversion, and after years of ownership that's usually a small number. Strip out land and there may be $250,000 or less of building basis. A cost segregation study reaches the new $230,000 of work, not the property. Worth doing, not transformative.

Verdict: strongest position in this conversation. Convert, hold, protect the first.

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Buyer Two: The owner without the rate advantage

Same Prop 13 basis. But he bought with cash, or refinanced in 2024, or is carrying something near market anyway.

Everything about Buyer One applies except the constraint that defines her.

He has a real option she doesn't: a HomeStyle or 203(k) refinance is genuinely on the table. Roll the purchase debt and the construction into one loan underwritten against after-improved value, at a rate that isn't materially worse than what he's already paying. One loan, one payment, no second lien, and construction financed against value the conversion creates.

Verdict: same excellent property tax position, more financing flexibility. Run the refinance math — for him it might win.

The difference between Buyer One and Buyer Two is nothing about the property. It's one line on an existing loan.

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Buyer Three: The owner-occupant buyer

She doesn't own it yet. She'd buy at $950,000 and live in the main house while converting.

What she has: the best financing available in American real estate, and most people never learn it exists.

An owner-occupant living in one unit of a two-to-four unit property qualifies for 5% down under Fannie Mae. On $950,000 that's $47,500. An investor buying the identical building needs 25% — $237,500.

She avoids the investment property loan-level price adjustment entirely, which runs roughly half a point to a full point of rate for the same borrower on the same house. She needs about two months of reserves rather than six.

And through FHA 203(k), HomeStyle, or Freddie Mac's CHOICERenovation, she finances the purchase and the conversion in a single thirty-year mortgage underwritten on after-improved value. She submits plans and bids before escrow closes, and the appraiser values the property as it will exist with three units.

She is borrowing against equity the conversion hasn't created yet. For a strategy whose central problem is that construction cash goes out before value comes in, that's the answer.

What it costs her: she has to actually live there. Occupancy within 60 days of closing, 90 if renovation delays it, as a genuine primary residence. Scope approved in advance, draws inspected, changes requiring lender sign-off. And on a 203(k) specifically, she cannot use a contractor she's related to or in business with.

What she gives up in return: full reassessment at purchase price. Her taxes run roughly $12,400 against Buyer One's $6,600. Yield on cost lands near 4.6% rather than 10.3%.

Verdict: for someone without $250,000 sitting in cash, this is the only version of buying that works. Buy, convert, occupy, then move on and rent the main house too.

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Buyer Four: The pure investor

He'd buy the same house purely as an investment and never live there.

What he faces: 25% down on a two-to-four unit — $237,500 before construction. A rate half a point to a full point above owner-occupied pricing, driven by agency loan-level price adjustments that reach 4.125% of the loan amount at higher leverage. Six months of reserves on the subject property plus two months for every other financed property he owns, in his own accounts, no gift funds. And no access to any of the renovation products, because all of them require owner occupancy — so construction gets funded separately, in cash or through a construction loan.

Full reassessment. Roughly 4.6% yield on cost. Thin cash flow at best.

What he gets that nobody else does: basis.

He establishes basis at $950,000. Strip out land at 30% to 40% and he still has $570,000 to $665,000 of building basis, none of it eroded by depreciation anyone has already taken. Add $230,000 of conversion.

A cost segregation study runs against $800,000 to $900,000 rather than $230,000. At a 25% to 35% reclassification, with 100% bonus depreciation permanently restored under the One Big Beautiful Bill Act for property placed in service after January 19, 2025, that's $200,000 to $300,000 of first-year deduction.

Three to four times Buyer One's tax position, precisely because he has no history.

Verdict: worst yield, best deduction. This works for someone with an ordinary income problem who can clear the passive loss hurdle — not for someone shopping for cash flow.

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The whole thing on one page

| | Down / capital | Property tax | Financing edge | Depreciation | Best for | |---|---|---|---|---|---| | Low-rate owner | Second lien or cash | ~$6,600 | Protects a 4% first | Small | Cash flow | | Owner, market rate | Refi or second | ~$6,600 | Refinance is viable | Small | Cash flow, simpler structure | | Owner-occupant buyer | 5% down | ~$12,400 | After-improved-value financing | Large | Getting in without capital | | Investor buyer | 25% down + construction | ~$12,400 | None | Largest | Sheltering income |

Same $950,000 house. Same $230,000 conversion. Same $7,800 in rent.

Two of these people should be optimizing for monthly income. One should be optimizing for access. One should be optimizing for a deduction. They should all be reading a different line of the same spreadsheet.

The question to ask before anyone draws plans

I'm a broker, not a lender, and the four situations above resolve into a conversation with a mortgage professional rather than a conclusion I can hand you.

But the question that conversation has to start with is the one nobody asks:

"What does my existing loan cost me if I refinance to build this?"

For Buyer One that's a $13,000-a-year answer, and if she finds it out after the plans are drawn she has already lost half the return. For Buyer Two the answer might be nothing, which opens a door. For Buyer Three the question doesn't apply, because she's buying and financing at once. For Buyer Four the renovation products aren't available at all.

Four people, one house, four answers — and the answer turns almost entirely on what you're carrying before you start.

Ask a mortgage broker that question early. Not after the contractor bids come in. Before.

This article is general information and not lending, legal, or tax advice. All figures are illustrative and will differ from your property, your loan, and your market. Loan program terms, county limits, and agency pricing change frequently, and eligibility depends on credit, income, reserves, and the specific property. Verify current terms with a licensed mortgage professional. Consult your attorney and CPA on ownership and tax questions, and licensed contractors on construction costs.