How much does a prefab ADU cost?
Last updated November 2, 2026 · Prices from 1,645 Structofy listings
Small homes in typical ADU sizes (about 250 to 1,200 square feet) on Structofy have a median asking price of $171,000 across 68 priced listings. Expect to add foundation, utility connections, permits and delivery, which can be significant in a tight backyard.
What counts as an ADU?
An accessory dwelling unit, or ADU, is a second, smaller home on the same lot as a main house, such as a backyard cottage, garage apartment or granny flat. Many prefab builders sell models specifically sized for backyards, and many small modular and pre-fab houses can work as ADUs where local rules allow.
Because Structofy listings do not all use the ADU label, the numbers on this page use homes in a typical ADU size range, excluding tiny houses, barns, commercial buildings and HUD-code homes. 31 listings explicitly mention ADU use.
Prefab ADU prices by size
| Group | Listings | With a price | Lowest | Median | Highest | Median $/sq ft | Median size |
|---|---|---|---|---|---|---|---|
| ADU-size homes (250–1,200 sq ft) | 125 | 68 | $21,908 | $171,000 | $500,000 | $236 | 832 sq ft |
| Listings that mention ADU | 31 | 27 | $21,908 | $156,000 | $500,000 | $264 | 608 sq ft |
| 250–599 sq ft | 80 | 44 | $21,908 | $106,000 | $274,800 | $249 | 447 sq ft |
| 600–1,200 sq ft | 378 | 54 | $59,905 | $180,000 | $500,000 | $211 | 1,013 sq ft |
Source: 1,645 home listings on Structofy, as published by each builder, read when this page loads. Prices are the builder’s listed base price; listings without a price are counted but not used for price figures. Median means half the listings cost less and half cost more. These are listing prices, not finished project costs.
ADU-size listings work out to about $236 per square foot for the unit, with a median size of about 832 square feet.
Example backyard-size homes
Here is a spread of real listings in ADU sizes from different builders. Check each builder's page for available options and service areas.
| Model | Builder | Type | Size | Beds | Listed price | $/sq ft |
|---|---|---|---|---|---|---|
| Sitka ADU Kit | DC Structures | Pre-Fab House | 405 sq ft | 1 | $21,908 | $54 |
| Summit 308 ADU | Studio Shed | Pre-Fab House | 308 sq ft | – | $92,173 | $299 |
| Barnhouse 2.1 Prefab Kit | Den Outdoors | Pre-Fab House | 1,000 sq ft | 2 | $154,750 | $155 |
| Yellowstone | Zip Kit Homes | Modular | 756 sq ft | 2 | $176,900 | $234 |
| ModHoff 740 | ModHoff | Urban | 740 sq ft | 2 | $185,000 | $250 |
| Vista Modern | Sand Creek Post & Beam | Modern | 960 sq ft | 2 | $198,000 | $206 |
| Abodu Studio | Abodu | Modular | 385 sq ft | – | $234,800 | $610 |
| Fernie | Dvele | Pre-Fab House | 705 sq ft | 1 | $310,000 | $440 |
Source: 1,645 home listings on Structofy, as published by each builder, read when this page loads. Prices are the builder’s listed base price; listings without a price are counted but not used for price figures. Median means half the listings cost less and half cost more. These are listing prices, not finished project costs.
The costs on top of the unit
Backyard sites are often tight, so site costs can make up a large share of an ADU budget. Ask both the builder and a local contractor to walk the site before you commit.
- Foundation. Slab, piers or crawlspace, depending on the unit and soil.
- Utilities. Running water, sewer and electric from the main house, and possibly a separate meter or panel upgrade.
- Access and crane. Narrow side yards, fences, trees and power lines can make delivery harder and more expensive.
- Permits and fees. Building permits, plan review and, in some areas, impact or utility connection fees.
- Finish work. Steps, decks, paths and landscaping.
Rules to check first
ADU rules are set locally and vary widely. Common limits include maximum size, setbacks from property lines, height, parking, owner-occupancy requirements and whether the unit can be rented.
Many states and cities have relaxed ADU rules in recent years, but always confirm the current rules with your planning department before choosing a model.
Is a prefab ADU worth it?
A prefab ADU can add living space for family, a home office or rental income with less disruption to your property than a fully site-built addition, since much of the work happens in a factory. Rental income and added property value depend entirely on your local market, so run the numbers locally.
For financing options such as home equity loans, see our prefab financing guide, and for smaller units, see tiny house costs.
Frequently asked questions
How much does a prefab ADU cost?
ADU-size homes on Structofy have a median asking price of $171,000 for the unit, before foundation, utilities, permits and delivery.
Is a prefab ADU cheaper than a site-built ADU?
It can be, mainly through shorter on-site construction time, but site work, utilities and permits are needed either way.
Can I rent out a prefab ADU?
In many areas, yes, but some cities restrict short-term rentals or require the owner to live on the property. Check local rules.
How big can an ADU be?
Size limits are set locally and often depend on lot size and the size of the main house. Your planning department can confirm the maximum.
Keep exploring
Structofy is a directory of factory-built homes and does not build, sell or finance homes. General information on this page is not financial, legal or building advice; confirm details with builders, lenders and your local building department.