Numbers & Deals · Arthur the Developer · 17K views

My $403,000 Duplex - Construction Cost Breakdown

A real duplex build opened up line by line: land, construction, fees, and what was left as profit.

Real numbers from a real $403,000 duplex build, opened up line by line in the video. Here’s how to read a cost breakdown like a developer.

The cost stack

Every build reduces to three buckets: land, construction (including the builder’s fee), and transaction costs on exit. Profit is what the sale price leaves after all three. The discipline is deciding those numbers before you buy, not discovering them after.

Run your own numbers

The developer’s formula: sale price minus land, construction, and ~3% selling costs. Investment build assumes ~10% down + closing.

Target sale priceLand costConstruction + builder fee

$97,500

Est. profit

18%

ROI on cost

20%

Land % of sale

136%

Cash-on-cash

Rules of thumb from the BuildUp playbook: land at 20-25% of sale price or less, and a minimum 20% ROI (target 25%) before breaking ground. Red numbers mean the deal doesn’t pencil yet. Estimates only, not financial advice.

Why duplexes pencil

Two doors on one lot spreads the land cost across two units, and duplexes give you exit flexibility: sell both, rent both, or live in one and rent the other. Several of our community members chose a duplex as their first project for exactly that reason.

A duplex is often the smallest project with a built-in plan B. That flexibility is worth as much as the margin.

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Common questions

What does it cost to build a duplex?

This one came to about $403,000 all in, for two units of 1,495 square feet each, so just under 3,000 square feet total, each side a 3 bed 2.5 bath with a one-car garage. That is construction from permits through final clean, and it does not include the land, the site development, or the builder fee.

What are the biggest line items in a build?

Framing and finishes. On this duplex: lumber package $35,857, drywall $20,500, HVAC $19,926, framing labor $16,489, electrical $14,999, millwork $14,787, plumbing $14,776, cabinets $14,875, paint $13,000, siding material about $12,500, excavation $11,525, insulation $11,295, and foundation $11,350.

How can architectural fees be so low on a 3,000 square foot building?

By replicating the plan. Architecture came to $1,075 and structural engineering to $1,350 because one building design was used four times with different exterior looks. The design was paid for once, and each additional site only needed an hourly rate for the submittal and a separate engineering memo per address.

What costs get forgotten in a construction budget?

The connection fees and the small stuff. This build paid roughly $7,600 in sewer fees and $7,400 for water and the meter install, plus $4,785 in permit fees, $750 for geotech soil compaction, $700 for survey, and $1,226 for temporary power. Final cleans added about $1,700 across three separate cleans.

What is the cost per door on a multi-unit project?

About $200,000 per door across the eight units in phase one, so roughly $1.6 million of construction. Add the builder fee on top, typically 8% to 15% with 8% to 12% being the usual range. Land and site development costs are separate again.

Nationwide