Quick answer
A manufactured ADU is a manufactured home, built in a factory to the federal HUD Code on a permanent steel chassis, that is placed on a lot as an accessory dwelling unit beside the main house.
In California the ADU law names manufactured homes as a type of ADU, so the city must treat one like any other ADU application. The building rules come from the federal government, not the state building code.
Quick facts
- Built to
- Federal Manufactured Home Construction and Safety Standards, 24 CFR Part 3280 1
- Federal size test
- 8 ft or more wide or 40 ft or more long in travel mode, or 320 sq ft or more when set up 1
- Frame
- Permanent chassis; designed for use with or without a permanent foundation 1
- California ADU status
- Included in the ADU definition, Gov. Code 66313(a)(2) 4
- California definition used
- Health and Safety Code 18007: built on or after 15 June 1976 6
What "manufactured" means, in plain English
"Manufactured" is a legal term, not a style. It means the home was built in a factory to one national rulebook, the HUD Code. HUD is the US Department of Housing and Urban Development.
Under the federal definition in 24 CFR 3280.2, a manufactured home can be moved in one or more sections. In travel mode it is at least 8 body feet wide or 40 body feet long.
Or it is at least 320 square feet once set up. It sits on a permanent chassis (a steel frame under the floor). It is designed as a home, with or without a permanent foundation, once connected to utilities.
The HUD Code covers the structure, plumbing, heating, cooling and electrical systems built into the home. A self-propelled RV is excluded.
Homes built before the HUD Code took effect are usually called mobile homes. California's definition in Health and Safety Code 18007 covers homes built on or after 15 June 1976. That is why "mobile home ADU" is a common search but a dated label 6.
Sources: [1]
Why it matters to you
The label decides who checks the building. The factory and HUD's inspection system cover the home itself. Your city covers where it sits, what holds it up and how it connects to water, sewer and power.
It also shapes your loan, your insurance and resale. Lenders and insurers may treat a manufactured home differently from site-built floor area. Ask them early, before you buy a unit.
And it decides whether an old unit can be used at all. In California a home built before 15 June 1976 does not meet the definition the ADU law points to.
How to tell a home is HUD Code certified
| Marking | Where it is | What it shows |
|---|---|---|
| Certification label (often called the HUD tag) | Outside, at the taillight end of each section, about 1 ft up and 1 ft in from the road side 3 | A metal plate, about 2 by 4 inches, with a three-letter code and six-digit number certifying the section was built to the federal standards |
| Data plate | Inside, near the main electrical panel or another visible spot 2 | Plant name and address, serial number, model, date made, label numbers and design loads |
California's rule: a manufactured home counts as an ADU
California's ADU law defines an ADU as an attached or detached home with complete independent living facilities. It then says an ADU also includes an efficiency unit and "a manufactured home, as defined in Section 18007 of the Health and Safety Code".
That is Government Code 66313(a), as amended by SB 543 (Stats. 2025, ch. 520), effective 1 January 2026. The same rule sat in former Gov. Code 65852.2 before SB 477 moved the ADU law into Chapter 13 in 2024.
In practice the city reviews a manufactured ADU under the same ADU standards as a site-built one: size limits, setbacks, height and utility rules in the ADU regulations. The difference is the building review. The home is already certified, so local review focuses on the foundation or support system, hookups and installation.
Foundations have their own state rule. Health and Safety Code 18551 tells HCD to set statewide rules for manufactured home foundation systems, and those rules replace local ones. A manufactured home may be installed on a foundation system as a fixture or improvement to the real property.
Important distinction
A manufactured home is built to the federal HUD Code on a permanent chassis. A modular (factory-built) home is built to the state building code. An RV is a vehicle. Only the first two can be ADUs in California, and they go through different reviews.
Rules in other states
The HUD Code is national, so the home itself is built to the same standard everywhere. What differs is the ADU law and local zoning.
Some states do not name manufactured homes in their ADU laws. Some local zoning codes limit where they can go. Check before you buy. See ADU laws by state.
How a manufactured ADU gets approved and installed
- Screen the lot with the feasibility checker and measure the delivery route.
- Pick a unit and confirm the certification label and data plate.
- Draw a site plan and a foundation or support design for the permit.
- Apply. In California the city must say within 15 business days whether the application is complete, and decide a complete one within 60 days when a home already stands on the lot (Gov. Code 66317) 5.
- Build the foundation and run utilities to the pad.
- Deliver, set and tie down the home, connect utilities, and pass final inspection.
Worked example: checking a used unit
A hypothetical owner in California finds a used manufactured home for sale. This is how the paperwork check plays out.
| Check | What they find | Result |
|---|---|---|
| Certification label on each section | Present on both halves | Pass 3 |
| Date made on the data plate | 1974 | Fails the 15 June 1976 cut-off in Section 18007 6 |
| Second unit, same seller | Label present, made 1998 | Can be considered under Gov. Code 66313(a)(2) 4 |
| Attached deck planned | Data plate says the home IS NOT designed for attached structure loads | Deck must be free-standing, or redesigned 2 |
- If No certification label on a section
- Then Stop: you cannot show it was built to the HUD Code
- If Data plate shows it was made before 15 June 1976
- Then Stop: it falls outside the Health and Safety Code 18007 definition
- If Label present and made on or after 15 June 1976
- Then Move on to the city's ADU standards and the foundation system
- If You plan a deck, porch or garage attached to it
- Then Read the data plate first; if it is not designed for attached loads, build free-standing
California only. A paperwork screen before you pay; the city still reviews the installation. Source: [3] [6] [4]
The first home cannot be an ADU under California's definition, however good its condition. The second can move to the permit stage, but the plan has to change for the deck.
Manufactured vs factory-built (modular) vs RV
| Manufactured home | California factory-built (modular) | Recreational vehicle | |
|---|---|---|---|
| Built to | Federal HUD Code 1 | California Building Standards Code 8 | Not a home standard |
| Chassis | Permanent chassis | None; set on a foundation | Wheels or chassis |
| Proof | HUD certification label | HCD insignia of approval | Vehicle registration |
| Counts as an ADU in California? | Yes, by name in Gov. Code 66313(a)(2) 4 | Yes, if it meets the ADU definition; see prefab ADU | Not named; see tiny home ADU |
How the pieces connect
- HUD Code certification → delivery on its chassis → local ADU permit (zoning, site plan, foundation) → utility connection → final inspection
Where you will see it on paper
- Sales listing: serial number, label numbers and year made. Missing numbers are a warning sign.
- Permit set: a site plan, foundation or support drawings, and the home's install instructions.
- Loan offer: the lender may ask whether the home is a fixture of the land. See ADU financing.
- Insurance quote: the policy type may differ from a site-built ADU.
What drives the cost
HyreADU does not publish a manufactured ADU price. We have no dated, sourced dataset that fits.
The drivers are clear, though. Delivery depends on the route and whether a crane is needed. The foundation or support system depends on soil and slope.
Utility runs depend on distance to the sewer, water and electric service. Permit and impact fees apply as for any ADU. Try your own inputs in the ADU cost calculator and see ADU costs.
Reasons people choose one, and the catches
What it does well
- The home is complete when it arrives, so site work is mostly foundation and hookups.
- California cannot refuse it just for being a manufactured home, because the law names it as an ADU.
- Built to one national standard, so used and new units can be compared by label and data plate.
Where it falls short
- Transport size limits shape the floor plan; tight lots may not allow delivery.
- Lenders and insurers may treat it differently from site-built square footage.
- Older units may predate the HUD Code and will not qualify under California's 1976 cut-off.
Common misreadings
- Myth Any mobile home can be an ADU.
- Reality In California only homes meeting Section 18007, built on or after 15 June 1976, fit the definition 6.
- Myth A manufactured ADU needs no permit.
- Reality The home is certified, but the foundation, hookups and placement still need a local permit.
What to ask before you buy a unit
- Can I see the certification label on every section and the data plate?
- What is the build date? In California it must be on or after 15 June 1976 6.
- Is the home designed for attached decks or porches? The data plate says 2.
- How does the planning department review the foundation or support system?
- Will the transport width and length clear gates, trees and power lines?
- Who will do the site work, and is that contractor licensed?
Your manufactured ADU checklist
- Confirm your lot allows a detached ADU.
- Find a unit and photograph the label and data plate.
- Ask your lender and insurer how they treat it.
- Get a site plan and foundation design drawn.
- Price the site work in writing; compare bids with the bid comparison tool.
- Apply for the permit and track the city's deadlines.
- Schedule delivery only after the foundation passes inspection.
Key takeaways
- A manufactured home is built to the federal HUD Code on a permanent chassis.
- California's ADU law names manufactured homes as ADUs (Gov. Code 66313).
- Homes built before 15 June 1976 do not meet California's definition.
- The city still permits the foundation, hookups and placement.
Related guides, tools and research
- All ADU typesWhere manufactured fits among the options
- Prefab building standardsHUD Code vs state factory-built approval
- ADU type selectorWhich type suits your lot
- ADU permitsWhat the city checks
Questions about manufactured adu
Can a manufactured home be an ADU in California?
Yes. Government Code 66313(a)(2) says an ADU includes a manufactured home as defined in Health and Safety Code 18007. The city then applies its normal ADU standards for size, setbacks and utilities.
What is the difference between a manufactured home and a modular home?
A manufactured home is built to the federal HUD Code on a permanent chassis. A modular home in California is factory-built housing built to the state building code. It carries an HCD insignia instead of a HUD label.
Is a mobile home the same as a manufactured home?
In everyday talk, yes. Legally, manufactured home means a HUD Code home. California's definition covers units built on or after 15 June 1976, so older mobile homes do not count.
Does a manufactured ADU need a permanent foundation?
The federal definition allows use with or without one. In California, HCD sets statewide foundation system rules, and a home can be installed as a fixture of the land. Ask your building department what it requires.
Where is the HUD label on a manufactured home?
The certification label is outside, at the taillight end of each section, about one foot up from the floor and one foot in from the road side. The data plate is inside, usually near the main electrical panel.
Can I use a used manufactured home as an ADU?
Often, if it has its labels and data plate and meets your state's definition. In California it must be built on or after 15 June 1976. Have it inspected for condition before you buy.
Can I add a porch or deck to a manufactured ADU?
Check the data plate. It must say whether the home is designed for the extra loads of an attached structure. If it is not, a deck has to stand on its own supports.
How long does approval take in California?
The city must tell you within 15 business days whether your application is complete. It must approve or deny a complete application within 60 days when a home already stands on the lot (Gov. Code 66317).
Sources
- eCFR, 24 CFR 3280.2 (HUD Code definitions: manufactured home), retrieved .
- eCFR, 24 CFR 3280.5 (data plate), retrieved .
- eCFR, 24 CFR 3280.11 (certification label), retrieved .
- California Legislature, Government Code 66313 (ADU definitions, as amended by SB 543, effective 1 Jan 2026), retrieved .
- California Legislature, Government Code 66317 (completeness notice and 60-day decision, as amended by SB 543, effective 1 Jan 2026), retrieved .
- California Legislature, Health and Safety Code 18007 (manufactured home), retrieved .
- California Legislature, Health and Safety Code 18551 (manufactured home foundation systems), retrieved .
- California Legislature, Health and Safety Code 19971 (factory-built housing), retrieved .
Expert review
Written by the HyreADU Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Federal definitions, data plate and label rules read on eCFR; California definitions, foundation rule and review deadlines read on the current statute text at leginfo.legislature.ca.gov on 7 October 2026. The worked example is hypothetical. No prices or lender rules stated as fact.
Suggest a correction. We fix errors and say what changed.