ADU
How Much Does an ADU Cost in 2026? Prefab Prices by Size, and What It Costs to Build an ADU
Oct
Your ADU cost starts with the home, then adds the work your lot needs. We’ll walk you through our 2026 prefab prices, from $137,800 to $240,700, what delivery includes, and the costs your contractor quotes separately.
Your ADU cost is easier to work out when you separate the home from the work on your lot. Broad averages mix garage conversions in one city with custom two-story homes in another. We sell prefab ADUs with listed prices, so we can give you a clear starting number. Prefab means the home is built at a factory before delivery. Here is what we can price, what we can estimate for your address, and what your contractor adds when you compare the cost to build an ADU.
ADU cost in 2026: the short answer
Our prefab homes range from $137,800 to $240,700, depending on size and layout. An accessory dwelling unit, or ADU, is a second home on your property. The price covers the finished home, delivery and a crane placing it on your foundation within the first 250 miles from the factory in Spanish Fork, Utah. In California, that distance is 650 miles. Your kitchen, bathroom, flooring, windows, doors, heating and chosen finish series are included. Your contractor quotes the foundation, utility connection, permit and site prep separately. Add both quotes for the total cost of an ADU in your yard.
ADU cost by size: every unit we sell
Each home below is a detached ADU, meaning it stands apart from your main house. Irontown Modular builds them to the same building codes as a house built on your lot. These prices cover the Designer finish. Each product page also prices three other looks.
| Unit | Square footage | Beds / baths | Price, delivered and set |
|---|---|---|---|
| Mysa 500 | 497 sq ft | 1 / 1 | $137,800 |
| Cabana 500, ready to ship | 497 sq ft | 1 / 1 | $160,000 |
| Cabana 700 | 638 or 718 sq ft | 2 / 1 or 2 / 2 | $170,900 |
| Sledhaus 500 | 580 sq ft plus loft option | 1 / 1 | $174,200 |
| Cabana 500 | 497 sq ft | 1 / 1 | $179,700 |
| Torrey Flats | 696 sq ft | 1 / 1 | $188,200 |
| Eagle Landing 1000 (Utah only) | 1,000 sq ft | 2 / 2 | $221,100 |
| Rabbit 1000 (two story) | 1,000 sq ft | 2 / 2 | $232,300 |
| Morada 800 | 793 sq ft | 1 or 2 / 1 or 2 | $236,100 |
| Morada 1000 | 989 sq ft | 1 or 2 / 1 or 2 | $240,700 |
Square footage is only one cost driver. The Mysa 500 and Cabana 500 both have 497 square feet, but their prices are $41,900 apart. The Mysa has a cabin look. The Cabana has a cleaner modern layout with full-size features throughout. The Cabana 700 gives you two bedrooms for less than the one-bedroom Torrey Flats or Sledhaus 500 because it uses a more compact layout. The ready-to-ship Cabana 500 is finished and waiting at the factory. It is $19,700 below the same plan built to order, with finishes already chosen and installed.
ADU cost per square foot
Our delivered and placed homes range from about $215 per square foot for the larger two-bedroom plans to about $360 for the smallest one-bedroom. Small homes cost more per foot for the same reason studio apartments do. The kitchen and bathroom cost the same whether the home has 400 or 1,000 square feet. Keep that in mind when comparing a 700 sq ft plan with an 800 sq ft plan. The extra space is the least expensive part of the building.
What a 500 sq ft ADU costs
Five hundred square feet is the size most people search for. Many cities allow that size without extra review, and it fits one bedroom, a full kitchen and a full bathroom. We have three homes around that size. The Mysa 500 with rustic or modern finishes costs $137,800. It is our least expensive 497 square foot 1-bedroom. The Cabana 500 with a covered front porch costs $179,700. It has a modern sloped roof, a private bedroom and a living room that opens into a full kitchen with space for a stacked washer and dryer. The Sledhaus 500 with an included deck costs $174,200. It has 580 square feet on the main level and an optional loft, an upper-level space. For this size group, you pay us $137,800 to $179,700 for the home, delivery and placement, before your contractor’s work.
Delivery and the crane
Delivery and crane placement are included within the first 250 miles from Spanish Fork, or 650 miles in California. Beyond the included distance, transport costs $12.75 a mile. A pilot car, which escorts the delivery vehicle, costs extra if needed. A lot 400 miles from the factory adds about $1,900, and one 1,000 miles away adds about $9,600. Irontown confirms your delivery figure during its feasibility review, a check of your lot and delivery route, before you commit. No sales tax is charged unless the home ships to Wyoming.
Permits, site prep, foundation and utility connection costs
Your soil, slope, distance to the sewer line and city fees determine this part of the bill. A website cannot price it for your lot. You can still ask an ADU builder or contractor for a clear cost breakdown covering each of these items:
- Feasibility review and permit. Irontown checks your lot and delivery route in one to two weeks and provides an ADU budget. You obtain the building permit. Irontown supplies stamped engineered plans, meaning plans approved by an engineer. These offer the same straightforward review as a city’s pre-approved ADU plans. Cities set their own plan-check and impact fees, charges for reviewing plans and the development’s effects on local services.
- Site prep. This covers clearing and leveling the spot and making sure the truck and crane can reach it. Access is the biggest surprise on ADU projects, so walk the route with your contractor first.
- A new foundation. Your contractor pours it to Irontown’s plans and has it ready before delivery.
- Utility connection. This covers digging trenches for water, sewer and power from your house or the street. Include a separate meter if you want one for a tenant.
- Joining and finishing. After crane placement, a local crew joins the sections, seals the seams and connects utilities. This is a short job for a single-section home.
- Outside the home. Paths, patios, fences and landscaping are easy to add later. They are also easy to overspend on now.
Ask for a price beside each item. Then ask how your contractor handles rock in a trench or a city requirement to upgrade the sewer. These are the hidden costs on most ADU projects, and a good contractor will explain how they handle them.
ADU cost by type: prefab, site-built and garage conversion
A detached home built on your lot is new construction priced for that job. It starts with an architect’s plans. Crews then spend months building the supporting structure, installing plumbing and finishing your home, with bills arriving as work progresses. Weather and material prices can change along the way. A prefab ADU build is priced before you order and happens indoors. Your site is the only variable, which makes prefab usually cheaper and always more predictable. A garage conversion can cost less than either option because the walls and concrete floor already exist. You lose the parking space, though. An older garage often needs a new foundation, insulation and plumbing before it qualifies as a home. For a detached home on a normal lot, prefab gives you the simpler bill.
How long it takes to build an ADU
There are three steps. The feasibility review takes one to two weeks. Next come two to three months of preparation for the site visit, your selections and the stamped plans. Building, shipping and placement take another 12 to 16 weeks. Your contractor handles the foundation and trenches alongside that work. Most homes are placed within about six months of ordering. The ready-to-ship Cabana 500 can leave once your foundation is ready.
Is an ADU worth the investment?
You can look at rental income and property value. A one-bedroom home with its own entrance rents as a full apartment. An appraiser counts a permitted ADU as a second livable home on your lot. Your property taxes rise by the value of the new home rather than the whole property. Whether the numbers work for you depends on the local rents you already know.
ADU financing: how people pay for it
The home sits on a permanent foundation, so you finance it like a house. Most homeowners use cash or savings, a home equity line that lets them borrow against their main house, or a construction loan that becomes a mortgage once the home is placed. Irontown is pre-approved with two lenders, Trillion Mortgage and Security Home Mortgage, for ADU and new-construction loans. Ask us for an introduction when you request your quote.
Getting your own number
Choose a home from the table and send us your address for a delivered price. Give that quote to your contractor to price the foundation and utility connections. Those two quotes give you one total. We are an authorized Irontown dealer with a 100 percent price match promise. Delivery and crane placement are included for the first 250 miles. There is no sales tax except in Wyoming. A real person checks your lot and route before you commit. If you are still deciding, read our guide to what an ADU is. When you are ready, request a quote and we will work out the ADU cost for your address.
