Splitting a duplex into two single family homes is a build-time decision, not a renovation. Tim Raybon, a general contractor and build-to-rent investor in Rutherford County, Tennessee, puts a two-hour firewall down the center line of every duplex he builds — even when code doesn’t require it — at a cost of roughly $6,000. After construction is finished, a surveyor comes back, locates the center point of the structure, and the parcel becomes two zero-lot-line single-family homes that can be sold separately.
That sequence is the whole play. A duplex sells to an investor at investor pricing. Two individually deeded homes can sell to owner-occupants, one at a time, and Raybon says that shift “ups your equity enormously.”
This guide covers the order of operations, the zoning and utility conditions that decide whether the strategy works on a given lot, the build specs Raybon uses so the finished units rent to anyone, and the financing discipline that keeps him from building at the wrong time.
Key takeaways
- The firewall goes in during construction, not after. Raybon spends about $6,000 extra on a two-hour firewall at the center line of every duplex, even where code does not require it.
- Confirm zoning before anything else — multifamily, single-family, or mixed use. The re-plat only works if the underlying zoning permits two separate parcels.
- A sewer line running near the lot does not mean the lot has a sewer tap. Get the municipality to scope it before you make an offer or you may be absorbing $20,000 to $30,000.
- Raybon builds one story, slab on grade, single-car garage, walk-in shower, and one bathroom with a wheelchair-width doorway so the same unit rents to a 20-year-old or an 80-year-old.
- He stopped building entirely when borrowing hit roughly 8.5%–9% against post-COVID material costs 20%–30% higher. His line: he won’t build a $250,000 unit for $200 a month.
From the Real Estate Pros Show
This article draws on an interview with Tim Raybon of Carol Kenny, LLC on the Real Estate Pros Show, hosted by Scott Bursey.
Why Two Deeds Beat One Duplex
A duplex has one buyer pool: investors. Two zero-lot-line single-family homes have two buyer pools — investors and owner-occupants — and you can sell them one at a time. That optionality is the entire argument for building the split in from day one.
Raybon has spent most of his career in construction, first as a brick and block layer, then as a realtor and general contractor building a rental portfolio for his family’s trust. He currently holds ten doors across four detached single-family homes and three duplexes. His duplexes are all built so they can be legally converted into what he calls villas.
“Even though they look like a duplex, they are two single-family homes, and you up your equity enormously,” he says. That is not a promise of a specific appraisal bump — it will depend on your market, your comps, and what owner-occupant demand looks like where you build. Treat it as exit optionality rather than a formula.
The practical difference shows up when you want liquidity. With a duplex, you sell the whole thing or you refinance it. With two deeded homes, you can sell one half to an owner-occupant at retail, keep the other as a rental, and never disturb the tenant on the side you’re holding. For a build-to-rent operator carrying a small portfolio with no partners and no outside capital, that flexibility matters more than a marginal difference in day-one rent.
The cost of buying that optionality is about $6,000 and one extra survey. It is one of the cheaper structural decisions in a new build.
The Two-Hour Firewall: What It Costs and Why It Goes In Early
The two-hour firewall at the center line is what makes each half of the building function as an independent structure rather than half of a shared one. Raybon installs one in every duplex he builds, and he is explicit that code does not require it in his jurisdiction. He does it anyway, for about $6,000.
This is not something you add later. Once the slab is poured, the framing is up, and the drywall is hung, retrofitting a rated assembly through the center of an occupied or finished building is a demolition project, not an upgrade. The wall has to be designed into the plan set before the foundation goes in.
Before any of that, Raybon confirms zoning. His words: “You have to obviously make sure it’s zoned for multifamily and then also single-family, multifamily, mixed use. You have to make sure your codes are correct, your zoning are correct.” If the parcel can only support one multifamily building and cannot be divided into two conforming single-family lots, the firewall buys you a better building but not a second deed.
Two things worth doing while you’re still in planning:
- Take the plan set to the local building department and confirm what a two-hour separation requires in your jurisdiction — assemblies, penetrations, and how the wall terminates at the roof.
- Ask the planning side, separately, what they require to create two parcels from one after the structure is complete. Building and planning often give different answers, and you need both.
Raybon also makes his subs verify current codes at the municipality before they start, specifically to avoid failed inspections and three-week delays waiting on a re-inspection.
When I build a duplex, I put a two-hour firewall in mine. I’m not required to, but I still put it in. It costs me about another $6,000. After I get the building built, I hire the surveyor to come back and find the center point of that building and then create two single-family homes. It’s no longer a duplex.
— Tim Raybon, Carol Kenny LLC, Rutherford County, TN
The Re-Survey and Re-Plat Sequence
The split happens after the building is finished, not before. Raybon’s order of operations is short and does not vary:
- Confirm zoning and code. Multifamily, single-family, or mixed use — and confirm the municipality will allow the parcel to be divided after construction.
- Build the duplex with the two-hour firewall at the center line, designed into the plans from the start.
- Complete construction and pass final inspections as a duplex.
- Bring the surveyor back. In Raybon’s words, he hires the surveyor “to come back and find the center point of that building and then create two single-family homes.”
- Record the new parcels. At that point they are two zero-lot-line single-family homes and can be sold individually.
The center point of the structure becomes the shared property line — the lot line sits at the firewall. That is what “zero lot line” means in practice, and it is why the wall placement has to be exact. If the firewall is six inches off the intended center line, the surveyor has a problem that cannot be fixed with a pencil.
Municipal rules on this vary widely. Some jurisdictions handle it as an administrative lot split, some require a full re-plat with a public hearing, and some will not permit it at all without a subdivision process. Utilities matter too — separately metered water, sewer, and electric make the split far cleaner than shared services. Confirm the path with your planning department before you buy the land, not after the roof is on.
Land Due Diligence: The Sewer Tap That Kills the Deal
Raybon’s first evaluation metric on any parcel is land cost. His second is utilities, and within utilities, one specific item does most of the damage: the sewer tap.
“Even though there may be sewer ran through that area, you may not have a sewer tap,” he says. A line in the street is not a connection to your lot. If the tap isn’t there, you are looking at $20,000 to $30,000 to get one — enough to turn a workable build into a bad one.
His fix is procedural: get the lot scoped by the local municipality before you make an offer, and get confirmation in writing that a tap either exists or does not. Water and electric are rarely the problem. It’s sewer, and it’s usually on parcels a little farther out from the core.
Septic creates a different and arguably worse problem for this specific strategy. You can build a duplex on a rural parcel and still zero-lot-line it, but then two separately owned homes share one septic field. Raybon’s concern is ownership: “Who owns the septic? If it goes out, which party takes care of it? What if the other party doesn’t have any money?”
That question gets answered in easements and shared maintenance agreements, and it becomes a title and disclosure issue every time one half sells. For a strategy built entirely on the clean separability of two homes, a shared septic field reintroduces exactly the joint ownership you were trying to eliminate. Raybon’s preference is municipal sewer, and for the split play it is the more defensible choice.
Build Specs That Keep the Split Units Rentable and Sellable
Raybon builds to one spec and does not deviate, because the same unit has to work as a rental today and as an owner-occupant sale later. His rules:
- One story only. He won’t build or buy two-story. His reasoning is operational: “Sooner or later you’re going to run into a situation where someone has flooded something upstairs, a toilet or a shower, and it’s going to be nothing but a big headache for at least six months.” That’s a tenant moving out, repairs, and an insurance conversation.
- Slab on grade, no crawl spaces.
- A single-car garage at minimum on every unit.
- A walk-in shower. His units typically have two bathrooms; at least one gets the walk-in.
- One bathroom with a doorway wide enough for a wheelchair. Not the whole house — just enough accessibility that the unit works for someone who needs it.
He is deliberate that this is not a grab-bar build: “The whole house doesn’t have to be that way, just enough that it’s handicap-accessible, that a 20-year-old can rent it, or an 80-year-old can rent it that is handicapped.”
The logic is market-specific and worth copying rather than the specs themselves. Rutherford County has a significant elderly population and a large young workforce at the same time — Nissan and its supplier network, a Verizon hub, and an Amazon hub. A one-story accessible unit with a garage serves both, which means Raybon is never fishing in a single demographic pool.
Run the same read on your own submarket. If your demand is entirely young workforce, accessibility features are a smaller lever. If you have both populations, building for the narrower one costs you a buyer pool on the eventual sale.
Financing, Reserves, and Knowing When Not to Build
Raybon funds his builds with his own working capital and has paused construction rather than build at bad numbers. When borrowing costs reached roughly 8.5% to 9% against post-COVID material and appliance packages running 20% to 30% higher, he stopped. His land was already paid for — held over ten years — and he still would not pull the trigger.
His threshold is blunt: “I don’t want to build a $250,000 unit and only get $200 a month for it.” That’s the discipline the firewall strategy depends on. A build that doesn’t cash flow isn’t rescued by better exit optionality.
On lenders, his guidance is to go local. National banks generally won’t fund a small operator’s ground-up build. “You need to partner up with a local bank, someone that can make a decision that day.” The specific relationship he names is the officer with a guaranteed lending line — the person who can approve without sending the file up the chain. Build that relationship at the bank where you already keep deposits, because they know your numbers.
Two more habits worth stealing:
- A 5% repair reserve. Raybon moves at least 5% of gross income into a separate repair account every month whether he spends it or not, and never touches it for anything else. He recently replaced an $8,200 HVAC unit without it registering as an event.
- Don’t borrow just because the equity is there. He estimates roughly $3 million in accessible equity and has not drawn on it. His reasoning: you have to pay it back, and if a major local employer leaves, the overextended operator is the one who gets hurt.
Cash flow is the constraint in his market. Appreciation-first buying works in places like San Diego; in Middle Tennessee, he says, the deal has to cash flow or you don’t do it.
Frequently asked questions
Can you split any duplex into two single-family homes, or does it depend on zoning?
It depends entirely on zoning and local subdivision rules. Raybon confirms zoning first on every project — multifamily, single-family, or mixed use — before he does anything else, because the re-plat only works if the jurisdiction will allow one parcel to become two conforming lots.
Some municipalities treat this as a routine administrative lot split; others require a full re-plat process. Separately metered utilities usually make approval simpler. Confirm the path with your planning department before you buy the land, and verify it applies to your specific parcel rather than the general zoning category.
How much does the two-hour firewall add to a duplex build?
Raybon’s number is about $6,000 in his Middle Tennessee market. That is the incremental cost of the rated assembly above what he would otherwise build, and he pays it on every duplex even though code in his jurisdiction does not require it.
Your cost will vary with local labor, the assembly your building department requires, and how the wall terminates at the roofline. Price it with your framer and drywall sub during plan review, not after.
Why does the firewall have to go in during construction instead of later?
Because a rated wall at the center line of a finished building cannot be added without gutting the building. The assembly has to run continuously and terminate correctly, which means it has to be in the plan set before the foundation is poured.
There is also a placement issue. The surveyor later sets the new property line at the center point of the structure, so the wall has to sit exactly where the lot line will go. A wall built off-center creates a survey problem that no amount of paperwork resolves cleanly.
What should I check on a lot before making an offer to build a rental duplex?
Land cost first, then utilities — specifically, whether the lot has a sewer tap, not just a sewer line running nearby. Raybon’s guidance is to have the local municipality scope it before you make an offer, because a missing tap can cost $20,000 to $30,000.
Also confirm zoning permits both the duplex and the later split, and check water and electric availability. On rural parcels, understand that septic creates shared-ownership questions between the two eventual homes that you will have to solve in easements and maintenance agreements.
Is a CLUE report worth requesting when buying an existing rental property?
Raybon treats it as non-negotiable. A CLUE report — Comprehensive Loss Underwriting Exchange — is obtained by the seller from their insurance carrier and lists claims filed on the property over the prior five years. His position: get one from the seller or don’t buy the house.
The reason is coverage risk. If a prior roof claim was repaired by someone unlicensed, your insurer may deny a future claim on that roof. The report surfaces who performed the work and what warranty, if any, came with it. He pairs this with trade-specific inspections — an electrician for the electrical, a roofer for the roof, a plumber for plumbing on anything over ten years old — rather than relying on a general home inspector to find everything in two hours.
The bottom line
If you are building a duplex this year, the one decision to make before the slab is poured is whether the center line will carry a rated firewall — take your plan set and your parcel to the building and planning departments in the same week and get both answers in writing, because the $6,000 is only worth spending if the jurisdiction will let you record two deeds at the end of it.
