Building a duplex costs $402,000 on average, with most people spending $293,000 – $549,000, according to Angi (2026 data).1 Corporate sibling HomeAdvisor (2025 data) publishes an identical $402,000 average and $293,000 – $549,000 normal range, with smaller duplexes as low as $128,000 and larger or more complex builds as high as $1,120,000. Matching figures between the sibling sites alone don’t establish independent corroboration.1,2 Fixr (updated August 2022) publishes a separate national average of $388,000 – scoped to a 3,000 sq.ft. side-by-side duplex with two floors – within a national average range of $285,000 – $537,000, a $142,500 low end (a 1,500 sq.ft. stacked duplex), and a $1,100,000 high end (a 5,000 sq.ft. high-end single-story side-by-side duplex). The sources price different scopes, and the pages state no shared sourcing.3 Prices below are national averages*.
*National averages, not local quotes. Your price depends on the duplex’s size, layout, materials, and local labor rates.
Demolishing an existing structure first? Leave suspect materials to accredited pros. According to the U.S. EPA, asbestos-containing materials may release fibers when they are disturbed, damaged, or removed improperly, and activities that disturb painted surfaces in older homes, buildings, and structures may create large amounts of lead dust. Where removal is needed, it should be done only by a trained and accredited asbestos professional.4,5
$402,000
national average (Angi + HomeAdvisor)
$293,000–$549,000
published range (Angi most people; HomeAdvisor normal range)
$388,000
national average, 3,000 sq.ft. side-by-side (Fixr)
$115–$240
per sq.ft., parts and labor included (Angi + HomeAdvisor)
What the sources say
| Source | Headline figures | Notes |
|---|---|---|
| Angi (2026 data, updated Oct 2026) | $402,000 average; most people $293,000 – $549,000; up to $1,120,000 | Corporate sibling of HomeAdvisor; headline, component, labor, and size tables identical to HomeAdvisor’s |
| HomeAdvisor (2025 data, updated Jun 2026) | $402,000 average; normal range $293,000 – $549,000; span $128,000 – $1,120,000 | Sibling-published figures identical to Angi’s; smaller builds as low as $128,000 |
| Fixr (updated Aug 2022) | $388,000 average; average range $285,000 – $537,000; low $142,500; high $1,100,000 | Average scoped to a 3,000 sq.ft. side-by-side two-floor duplex; separately published, pages state no shared sourcing; older data vintage |
Cost per square foot
Angi and HomeAdvisor report $115 – $240 per square foot, parts and labor included, for builds commonly ranging from 1,500 to 3,000 square feet (identical sibling-published figures).1,2 Fixr separately reports $95 – $220 per square foot, with most people paying around $130 per square foot for mid-range duplexes.3 The two per-square-foot spans come from different publishers and are kept separate rather than reconciled.
Cost by duplex size
Each publisher prices total construction cost by size on its own basis; identical sibling cells are one sibling-published figure, and the 4,000 and 5,000 sq.ft. rows where HomeAdvisor and Fixr agree exactly are separately published figures – the pages state no shared sourcing, and no further conclusion is drawn.1,2,3
| Duplex size | Angi (2026) | HomeAdvisor (2025) | Fixr (Aug 2022, labor included) |
|---|---|---|---|
| 1,000 sq.ft. | – | – | $95,000 – $220,000 |
| 1,500 sq.ft. | $172,500 – $360,000 | $172,500 – $360,000 | – |
| 2,000 sq.ft. | $230,000 – $480,000 | $230,000 – $480,000 | $190,000 – $440,000 |
| 3,000 sq.ft. | $345,000 – $720,000 | $345,000 – $720,000 | $285,000 – $660,000 |
| 4,000 sq.ft. | – | $380,000 – $880,000 | $380,000 – $880,000 |
| 5,000 sq.ft. | – | $475,000 – $1,100,000 | $475,000 – $1,100,000 |
Where the publishers differ (the 2,000 and 3,000 sq.ft. rows), each figure keeps its own publisher’s label; the difference is not explained by the sources.
Cost by layout type (Fixr)
Fixr prices the two duplex layouts per square foot, labor included. A one-up, one-down (stacked) duplex runs $95 – $135 per square foot, a one-story side-by-side $110 – $180, and a two-story side-by-side $130 – $220. Fixr describes the side-by-side as the most common and most expensive layout, since it needs a larger roof and foundation plus decentralized plumbing.3
| Layout | Cost per sq.ft. (Fixr, labor included) |
|---|---|
| One-up, one-down (stacked) | $95 – $135 |
| One-story side-by-side | $110 – $180 |
| Two-story side-by-side | $130 – $220 |
Construction cost by component
Angi and HomeAdvisor publish an identical per-square-foot breakdown of the major construction components (sibling-published figures):1,2
| Component | Cost per sq.ft. (Angi + HomeAdvisor) |
|---|---|
| Foundation (concrete slab) | $5 – $33 |
| Lumber and framing labor | $11 – $30 |
| Roof structure and materials | $3 – $6 |
| Flooring (material + install) | $4 – $15 |
| Exterior finish (siding) | $4 – $13 |
| Drywall installation and finish | $1.50 – $3.50 |
| Interior paint application | $1 – $3 |
| Heating and cooling (HVAC) | $3 – $6 |
| Electrical system setup | $4 – $9 |
| Plumbing rough-in and fixtures | $4 – $5 |
Angi also prices common per-unit items: windows $450 – $1,500 each, doors $225 – $1,900 each, cabinets $150 – $500 per linear foot, light fixtures $70 – $300 each, and appliances $2,500 – $6,800 per kitchen.1
Where the money goes (Fixr)
Fixr breaks a duplex construction budget down by share of project cost. Architect, structural engineer, and contractor fees come on top of the listed shares rather than being included in them:3
| Project component | Share of project cost (Fixr) |
|---|---|
| Foundation | 9% |
| Floor structure | 12% |
| Walls and exterior finish | 6%–10% |
| Roof | 10% |
| Windows and doors | 5% |
| Interior finish | 6%–10% |
| Flooring | 3%–5% |
| Interior features | 3%–5% |
| Bathrooms | 4% |
| Kitchens | 8% |
| Electrical | 10% |
| Plumbing | 12% |
Added fees: architect 10.5%–15% of project cost, structural engineer $500 – $20,000 as needed, contractor 25% of project cost.
Professional fees
The sibling pair and Fixr publish professional rates on different bases (hourly, percentage, and flat), so the columns are kept separate and are not directly comparable row by row:1,2,3
| Professional | Angi + HomeAdvisor (sibling-published) | Fixr (Aug 2022) |
|---|---|---|
| General contractor | 10%–20% of total project cost (e.g. $50,000 – $100,000 on a $500,000 build) | 25% of project cost (added) |
| Architect | $100 – $250 per hour, flat fee, or 10%–15% of construction costs | 10.5%–15% of project cost (added) |
| Structural engineer | $100 – $220 per hour | $500 – $20,000 per project, as needed (added) |
| Interior designer | $50 – $200 per hour | $75 – $450 per hour |
| Electrician | $50 – $130 per hour | – |
| Plumber | $45 – $150 per hour | – |
Additional costs
If the lot has an existing structure, demolition and clearing come first: Angi and HomeAdvisor report $3,000 – $25,000 depending on the size and complexity of what needs to come down (identical sibling-published figures).1,2 Fixr reports around $35,000 to add an attached garage to the build.3
Duplex vs other building types (Fixr)
Fixr compares total construction cost for related infill and shared-wall building types (labor included):3
| Building type | Cost (Fixr, labor included) |
|---|---|
| Duplex | $285,000 – $660,000 |
| Triplex | $427,500 – $990,000 |
| Fourplex | $570,000 – $1,320,000 |
| Townhouse | $111,000 – $222,000 |
See our guides to barndominiums, modular homes, ADUs, home additions, and house demolition for those projects.
Frequently asked questions
How much does it cost to build a duplex?
Angi and HomeAdvisor report a $402,000 national average, with most people spending $293,000 – $549,000 (Angi’s label; HomeAdvisor calls the same span its normal range). Fixr separately reports a $388,000 average scoped to a 3,000 sq.ft. side-by-side duplex with two floors, within an average range of $285,000 – $537,000.1,2,3
How much does it cost per square foot to build a duplex?
Angi and HomeAdvisor report $115 – $240 per square foot, parts and labor included. Fixr separately reports $95 – $220 per square foot, with most people paying around $130 for mid-range duplexes.1,2,3
Is a stacked duplex cheaper to build than a side-by-side?
According to Fixr, yes: a one-up, one-down stacked duplex runs $95 – $135 per square foot, while a two-story side-by-side runs $130 – $220, because stacking one apartment over the other reduces roofing and foundation work.3
How much does it cost to convert a single-family home into a duplex?
Fixr reports $80,000 – $100,000 for a conversion, depending on project size – plumbing, HVAC, and electricity need rerouting, and the new apartment needs a kitchen, bathroom, and separate entrance. Conversion is a different scope from new construction.3
What does demolishing an existing structure add?
Angi and HomeAdvisor report $3,000 – $25,000 for demolition and clearing when the lot has an existing structure, depending on size and complexity.1,2
Related guides
Architect Cost
Structural Engineer Cost
Home Addition Cost
Barndominium Cost
Modular Home Cost
House Demolition Cost
All cost guides
Sources
1. Angi — Cost to Build a Duplex (2026 data)
2. HomeAdvisor — Cost to Build a Duplex (2025 data)
3. Fixr — Cost to Build a Duplex (updated Aug 2022)
4. U.S. EPA — Protect Your Family from Exposures to Asbestos
5. U.S. EPA — Protect Your Family from Sources of Lead