How Much Does It Cost to Build a Duplex? (2026)

A duplex is one of the fastest ways to turn a single lot into two income streams. In 2026, most duplexes cost roughly $220,000 to $780,000 all-in to build, or about $140–$260 per square foot and $130,000–$350,000 per unit, before land.

Your exact number swings with three things above all: total square footage, whether the units are side-by-side or stacked, and your local labor and material rates. Below is how the cost breaks down and how to get a figure tuned to your lot.

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$130k–$350k per unit$140–$260 / sq ftRSMeans-based estimates

How Much Does It Cost to Build a Duplex? (2026)

2026 cost dataPer-unit + per-sq-ft

What drives the cost of a duplex

Total square footage — the single biggest lever; every extra 100 sq ft adds framing, roofing, MEP and finishes across the whole envelope.
Layout — a stacked duplex shares a foundation and roof and is usually cheaper per unit than two side-by-side units on a wider footprint.
Finish level — builder-grade cabinets and LVP sit at the low end; quartz, tile and custom millwork push you to the top.
Location — the same duplex costs far more in coastal California than in Texas or the Midwest due to labor, permits and code.
Duplex-specific extras — fire-rated separation between units and separate utility metering are costs a single-family build never carries.

Duplex cost per unit vs. per square foot

Investors think in cost per unit because it maps to rent and financing. A duplex delivers economies of scale a single-family home cannot — shared foundation, shared roof, one mobilization of every trade, one permit — so per-unit cost typically lands 10–20% below building two detached houses of the same size.

Per-square-foot figures are useful for quick comparisons, but always confirm what is included: a 'shell-only' quote is very different from a permit-ready, move-in number with MEP, finishes and site work.

Typical all-in duplex build cost by size (2026)

Duplex size	All-in build cost	Est. per unit
Compact — 2 × ~800 sq ft (~1,600 total)	$220k – $360k	$110k – $180k per unit
Standard — 2 × ~1,200 sq ft (~2,400 total)	$330k – $540k	$165k – $270k per unit
Large / upscale — 2 × ~1,600 sq ft (~3,200 total)	$480k – $780k	$240k – $390k per unit

Excludes land. 2026 construction ranges for standard site conditions. Get an exact, RSMeans-based number for your ZIP code below.

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Frequently asked questions

How much does it cost to build a duplex per unit in 2026?+

Most duplex units cost $110,000–$390,000 to build depending on size and finish, with $165,000–$270,000 typical for a standard ~1,200 sq ft unit. Building two units under one roof saves 10–20% per unit versus two detached homes.

Is it cheaper to build a duplex or two single-family homes?+

A duplex is almost always cheaper per unit — the units share a foundation, roof and utility trenching and go through one permit and one mobilization of each trade, for roughly 10–20% lower per-unit cost.

Does the estimate include land?+

No. These ranges are construction only. Land, demolition and unusual site work (steep grade, rock, long utility runs) are separate and vary by market.

How do I get an exact number for my lot?+

Run an instant cost report for a state-adjusted estimate, or start a development brief to get custom plans plus a full RSMeans-based breakdown.

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Tell us your lot and goals. A designer prepares custom, permit-ready duplex plans with MEP layouts and an RSMeans-based cost estimate, and contacts you within 1 business day.