Back to BlogTop Query

A per-square-foot rate is an output of somebody else’s budget, and a duplex is the building it fits worst

Top Query

A per-square-foot number is a quotient. Somebody finished a building, totalled what it cost on their lot with their plan and their spec, divided by their area, and published the result. Run backwards as an input, that quotient carries their parcel, their foundation, their finish level and their pricing year into a budget nobody can see them in. On a two-unit building it also carries an assumption that does not survive contact with the plan, because the items a duplex repeats are counted per dwelling unit and have nothing to do with floor area. What a construction lender reviews is a line-item budget against drawings and a specification. A rate multiplied by an area cannot be read line by line, cannot anchor a draw schedule, and contains nothing at all for the parcel.

The budget that is one multiplication long

The version that shows up on investor forums is easy to recognise. A first-time builder has a lot in South Florida, wants a side-by-side duplex, intends to live in one unit and rent the other, and is financing it with a construction-to-permanent loan. The budget he posts for review is land, plus a rate, times an area.

The replies argue about the rate. Some call it low, some call it high, several tell him to shrink the units until the total lands where he needs it. One contractor answers that it depends on the site and on the details in the floor plans, which is the correct answer and gets less attention than the numbers do. A later poster lists what can go wrong with the parcel itself: whether two units are allowed there, the flood elevation, whether the footprint fits the setbacks and coverage, impact fees, the wind code.

Nobody asks what the rate is a rate of.

Everything that goes wrong in that budget later is downstream of the question nobody asked.

The rate is an answer to a budget that was already finished

A published per-foot figure is arithmetic performed on a completed job. Somebody built a specific building, on a specific parcel, to a specific spec, in a specific pricing year, and divided the total by an area they measured according to a convention they did not state. Conditioned space only, or gross area including the garage, the covered entry and the balconies? The two divisors produce very different quotients out of the identical building.

So the figure arrives loaded. Inside it sit their site work and their fill, their foundation type, their finish level, their subcontractor pricing in the market of that year, their jurisdiction’s fees, and their area convention. None of that is legible in the quotient, which is what makes the quotient dangerous rather than merely imprecise. It looks like a fact about construction and it is a fact about somebody else’s project.

Used in the other direction it earns its keep. Build the line-item budget for the actual building on the actual parcel, total it, divide by your own area, then compare that result against what comparable projects landed at. Where the two disagree, you have a question worth chasing through the line items, and you have the line items to chase it through. Used first, as an input, the same figure is a guess with a decimal point on it.

A duplex repeats the expensive things that never scaled with area

The arithmetic breaks here, and it breaks by structure rather than by region. A house has a kitchen. A duplex has a kitchen in each dwelling unit. The same repetition applies to the bathrooms, the water heater, the HVAC system with its air handler and condenser, the electrical service and its meter, the water service and its meter, and the entry door assembly. Jurisdictions and utilities commonly assess their charges per dwelling unit as well, so the impact, connection and capacity items in a duplex budget are counted the way the units are counted, not the way the area is measured.

None of those costs care how large the rooms around them are. A kitchen in a compact unit and a kitchen in a generous one differ by cabinet run and countertop area, and they are identical in appliance count, rough-in count, circuit count and the number of times a plumber and an electrician have to show up.

Then there is the assembly a single-family house does not have at all. The two dwelling units are separated by a fire-resistance-rated assembly, and that assembly is designed, specified, detailed and inspected as a system rather than bought as a material. Side by side, it is a wall carried continuously through the structure to the roof or attic intersection, and it governs how the framing, the sheathing, the penetrations, the electrical boxes and the mechanical runs crossing it are detailed. Stacked, the same requirement lands in the floor and ceiling assembly, where it arrives with sound requirements and a structural depth the vertical version never needed.

No per-foot rate borrowed from a single-family build contains a line for any of it, because the building it came from had nothing to separate.

Which is why shrinking the units raises the rate

The forum’s advice to build smaller is right about the total and quietly wrong about the arithmetic used to test it. Reduce the floor area and the total does fall: less slab, less framing, less roof, less drywall, less flooring, less paint. The count of dwelling units does not move. The kitchens, the baths, the services, the meters, the per-unit charges and the separation assembly all survive the reduction intact.

So the smaller duplex spreads the same fixed count across less area, and the cost per foot goes up.

Anyone who then applies the original constant rate to the reduced area understates the smaller scheme, and understates it worst at precisely the moment the scheme was being cut to make a number work. The reduction gets approved on a figure that was already optimistic before the units got smaller, and the shortfall surfaces later, during construction, against a loan sized on the optimistic figure.

Quick Answer

Why does a per-square-foot rate fail on a ground-up duplex?

A per-square-foot rate is an output of a finished budget built on somebody else’s lot, plan and spec. Duplex budgets break it because the items that repeat per dwelling unit do not scale with floor area: kitchens, baths, water heaters, HVAC systems, electrical and water services, and the fire-resistance-rated separation the two units share.

The direction of the error is the part worth carrying into a meeting. Because the fixed count holds while the area varies, a rate lifted from a larger project understates a smaller one, and the smaller the units get the wider that gap opens. A budget that was trimmed by shrinking the plan is the budget most likely to be short.

The same mechanism is why the rate is still useful at the end. Divide your own completed line-item budget by your own area and the resulting figure is a number you can defend, because every assumption inside it is written on a line somewhere behind it.

Interior of a South Florida house stripped to studs with structural framing and mechanical rough-in exposed — A full gut with the rough-in open. Everything visible here — service runs, fixture rough-ins, equipment locations — is counted per dwelling unit in a duplex, and a second unit repeats all of it regardless of how large the rooms around it are.Investment Properties →

Validate the parcel before anyone validates the building

Order matters here for a blunt reason: parcel findings can redraw the plan or end the project, and a plan drawn before they land gets drawn twice. Zoning comes first, and the question is narrower than owners usually ask it. Not whether a duplex is possible, but whether two dwelling units are permitted by right in the district the parcel sits in. A use that needs a variance, a rezoning or a public hearing is a schedule risk and an outcome risk rather than a line item, and it belongs on a different page of the file. Density is settled in the district text, and our short answers on what sets unit count and on what really moves multi-family cost per foot cover that ground. With the answer confirmed, a boundary survey establishes where the lines actually run, and the footprint gets fitted inside the setbacks and the coverage limit before anybody falls in love with a floor plan.

Flood comes next, and specifically the finished floor elevation the parcel requires. That elevation is not a design preference, it is a foundation scope. Fill, stem wall or elevated slab, a different geotechnical answer, longer utility runs, a driveway that has to climb to meet a garage: all of it follows from a requirement that belongs to the address rather than to the building. Flood zone work covers how the designation is determined and who determines it. What matters to this budget is that the elevation is a parcel fact the foundation answers to, and it is available before the drawings rather than during their review.

Utilities and soils travel together in the same pass. Whether the parcel is on public sewer or needs an onsite system. Whether water is available at the frontage or a main extension or a tap is required, and what the utility charges to connect a new dwelling unit. Then bearing capacity, the wet-season water table, and whether the site needs muck removal or structural fill, which is the difference between a foundation somebody designs and a foundation somebody discovers.

Last in the parcel pass, the jurisdiction’s own money. Permit fees, impact fees, connection and capacity charges, and whatever mitigation or concurrency applies locally. These get obtained from the jurisdiction and the utility as written line items for this parcel at this unit count. They are never estimated, and they are never inside a per-foot rate, because they attach to the address and to the number of dwelling units rather than to the structure. How permitting works in Miami-Dade describes the review path those charges sit on.

Then the building, and the spec is two specs

Construction type leads the building decisions because it reaches the structural design, the schedule and the insurance classification simultaneously. Frame or block covers what each system settles downstream, and the choice belongs in the budget as a decision already made rather than as a note to resolve later.

Miami-Dade and Broward both sit inside the High-Velocity Hurricane Zone. Every opening, the roofing assembly and the connections tying the structure together are designed to that standard, with product approvals named on the drawings and verified at inspection. A rate borrowed from a build outside the zone contains none of that, and a plan drawn outside the zone usually has to be redrawn to carry it.

Configuration is the next fork, and side-by-side and stacked are different buildings rather than different layouts of one. They divide the foundation, the roof, the stair, the plumbing stack and the separation assembly differently, and the zoning envelope frequently decides between them before anybody prices either.

The finish spec is where an owner-occupant budget goes wrong most reliably, because there are genuinely two specs in the building. The unit the owner intends to live in and the unit he intends to rent are not specified to the same standard and should not be. Blended into a single level, the owner unit drags the rental spec up or the rental unit drags the owner spec down, and the building gets built to whichever one won. Allowances are the mechanism that hides the disagreement until selection time, and what a thin bid leaves out covers how that plays out inside a proposal.

The soft costs a rate has never contained

Design and engineering. The survey and the soils report. Permit and impact fees. Builder’s risk insurance. Interest accruing during construction against a loan on a property generating nothing yet. Closing costs on the land. None of that is construction, all of it is project cost, and a figure quoted for putting up a building has no line for any of it.

Contingency is the other omission, and it is not a percentage sprayed across a total. It attaches to named unknowns. Underwriting a project covers how that discipline works and what a draw inspector does with it. The point specific to a ground-up duplex is that most of the named unknowns live in the parcel rather than in the building, and nearly all of them are convertible into knowledge while the land contract is still inside its inspection period.

Quick Answer

What has to be validated in a duplex budget before anything else?

Validate the parcel before the building. Confirm that two dwelling units are permitted by right in the district, order a boundary survey, fit the footprint inside setbacks and coverage, get the required finished floor elevation, and confirm sewer or septic and water availability. Then get the jurisdiction’s own permit, impact and connection charges in writing.

Every one of those is cheap next to a design fee and every one of them can invalidate a design. A set of drawings produced before the envelope and the elevation are known is a set of drawings priced against assumptions, and the correction arrives after the money is committed.

The written part is not a formality. A zoning confirmation letter, an elevation certificate or determination, a utility availability letter and a fee schedule issued for the parcel are documents a lender can put in a file. A phone call to a counter is not, and it does not survive a plan reviewer disagreeing with it later.

Canal-front multi-family building in West Miami seen from the street after a full renovation — Our West Miami multi-family renovation. Different work from a ground-up build, and the same counting problem underneath it: on any multi-unit property the money follows the unit count and the parcel long before it follows the floor area.Ground-Up Construction →

What the construction file actually has to survive

A construction-to-permanent lender does not underwrite a builder’s confidence. It underwrites drawings, a specification and a contractor’s line-item budget. The appraisal is made subject to completion against those same drawings and specifications. Draws are then released against the line items as the work they describe gets built and inspected.

A rate times an area fails each of those in turn, and it fails them in sequence. There is nothing to review line by line, so the reviewer has no way to test any assumption inside it. There is no schedule of values, so there is nothing to build a draw schedule from and no way to fund the job in stages. And when the appraisal and the budget are laid side by side, the budget offers the appraisal no structure to be compared against.

The parcel confirmations end up in the same file, and a reviewer reaches for them early, because they are the items capable of invalidating everything drawn on top of them. A borrower who has them is answering questions. A borrower who has a plan and a rate is being asked for them.

A per-foot figure is a quotient from a job that is already finished. It works as a check on a line-item budget and it cannot produce one
In a two-unit building, unit count drives the expensive repeats. Floor area drives the cheap ones
Shrinking the units lowers the total and raises the cost per foot, so a constant rate applied to a smaller scheme understates it — at the exact moment the scheme was cut to fit a number
The rated separation between the two dwelling units is a designed and inspected assembly with no counterpart in any single-family rate
Parcel facts can redraw or end the plan, so they get confirmed before design is commissioned and before the inspection period on the land contract runs out
Jurisdiction and utility charges are obtained in writing for this parcel at this unit count. They are not estimated, and they are not inside anyone’s rate
A lender reviews drawings, a spec and a line-item budget, then funds against line items. A rate multiplied by an area gives that file nothing to hold on to

Where the money is best spent first

Verification is cheap while the land contract is still open and expensive the day after it closes, and that asymmetry is the only real leverage a first-time builder has. Use the inspection period for the survey, the zoning confirmation, the flood determination and the utility answers. Take a schematic plan drawn for that specific parcel and have a preliminary line-item budget built against it. Then divide by the area and see what the rate says about the work you actually intend to do.

Request a proposal and we will price the ground-up build line by line against your parcel, on a duplex or on a larger multi-family or mixed-use building, anywhere in Miami-Dade or Broward.

Frequently Asked Questions

Neither wins outright, because they move different costs in opposite directions. Side by side gives each unit its own slab and its own entry at grade, keeps the service runs short and independent, and puts the rated separation in a wall carried continuously up through the structure. Stacked covers the same total area with less foundation and less roof, which is why it appears on tight lots and wherever coverage limits bind, but it puts the separation into the floor and ceiling assembly, adds sound control, adds a stair and its enclosure, and hangs one unit’s plumbing above the other unit’s ceiling. Side by side is usually simpler to phase and easier to support with nearby sales evidence, because it reads to an appraiser as two ground-level homes. In practice the zoning envelope settles it first: setbacks and coverage press hardest on the side-by-side scheme, height and stair access on the stacked one, so the district text often chooses the configuration before the budget gets a vote.

As a starting point, yes. As a permit set, no, and the gap is larger than the price of the plan. A Florida submittal is reviewed for things a stock set does not contain: wind design for this site’s exposure and this building’s geometry, signed and sealed by an engineer licensed in Florida; product approvals for every opening, the roofing assembly and the structural connectors; energy calculations for the climate zone; a foundation designed against the soils report and the required finished floor elevation; and a site plan drawn on the boundary survey showing setbacks, coverage, drainage and the utility connections. Reviewers also expect the separation between units detailed on the drawings rather than referenced generically. What usually happens is that a Florida engineer redraws most of the structural sheets and the stock plan survives as layout and elevations, which is a legitimate way to buy design intent. Before purchasing, confirm the vendor releases editable files, because a set nobody can revise cannot be adapted to the parcel it has to be built on.

It opens a gap the borrower has to close, and the constructive move is choosing the form it takes rather than waiting to be told. The usual paths are a reduced scope issued as a priced written revision, additional equity into the project, or a re-specification that changes finish levels while the building stays as drawn. What causes trouble is an unpriced verbal reduction, because the appraisal was made against a specific set of plans and specifications and the draw schedule gets built from the budget. Let those three documents drift apart and every later draw turns into an argument about which one is current. A scope revision is also worth taking back through the appraisal rather than assumed to be neutral, since what was appraised was the drawings. Ask early what the review process for a revision looks like, because that answer, not the size of the gap, usually sets the schedule.

A demolition permit of its own, and most of its prerequisites are not demolition. Each utility disconnection has to be ordered, performed and signed off by the provider — power, water, sewer or the abandonment of an onsite system, and gas where it exists — and each one runs on that provider’s calendar rather than yours. Older structures need an asbestos survey by a licensed inspector before the permit issues, with notification requirements attached and abatement if anything turns up. Then debris disposal, erosion and sediment control, tree protection or a removal approval where a protected tree stands on the lot, and in some jurisdictions a hold until the replacement permit is confirmed so the lot is not left cleared and idle. Open or expired permits on the existing structure get closed out first. Raising a roof versus rebuilding covers the same prerequisites where the question is whether to demolish at all. Carry demolition as its own scope with its own schedule; it sits on the critical path ahead of everything else.

The onsite system is sized from design flow, and design flow is calculated from the dwelling units and bedrooms the building will have. A second unit therefore reopens the system permit rather than adding a plumbing detail, and that review belongs to the agency that permits onsite sewage treatment and disposal systems, not to the building department. It runs on its own clock, ahead of the building permit, and a design that assumes otherwise waits. The site also has to hold both the system and its replacement area at the required separations from wells, property lines, the building and any surface water, so a footprint that fits the zoning setbacks can stop fitting once the drainfield and its reserve are drawn on the same survey. Soil evaluation and the wet-season water table decide whether the system is conventional or has to be mounded or engineered, which is a parcel-driven cost with foundation-scale consequences. Where public sewer is available at the frontage the jurisdiction may require connection instead, so get the availability determination in writing before the design assumes either answer.