A duplex costs about $180,000 to $600,000 or more to build in 2026, or $100 to $200 per sq ft for a standard build. Side-by-side duplexes run about $130 to $220 per sq ft and stacked (over-under) duplexes about $100 to $180.
How much does a duplex cost by size?
| Total size | At $100/sq ft | At $150/sq ft | At $200/sq ft |
|---|---|---|---|
| 1,800 sq ft (2 x 900) | $180,000 | $270,000 | $360,000 |
| 2,400 sq ft (2 x 1,200) | $240,000 | $360,000 | $480,000 |
| 3,000 sq ft (2 x 1,500) | $300,000 | $450,000 | $600,000 |
Side-by-side vs stacked duplex
| Layout | Cost per sq ft | Notes |
|---|---|---|
| Side-by-side | $130–$220 | two ground-floor units sharing one wall; needs a wider lot |
| Stacked (up-down) | $100–$180 | smaller footprint and roof; needs fire and sound separation between floors |
Why can a duplex cost less per unit?
Two units share a foundation, roof, one or more walls and the lot, so each unit costs less than building two separate houses. You still pay for two kitchens, two sets of bathrooms, separate utilities and meters, and fire separation between units.
How do you finance a duplex?
If you will live in one unit, owner-occupant loans are often available for 2- to 4-unit properties. Investors usually need a larger down payment. During construction, most buyers use a construction loan.
Frequently asked questions
Is it cheaper to build a duplex or two houses?
A duplex, usually, because the units share land, foundation, roof and walls.
Does zoning allow a duplex?
Check your local zoning. Many single-family zones do not allow duplexes, though some states and cities have relaxed these rules.
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