ADU Buying Guide · 2026
Prefab vs Modular vs Manufactured Homes: The Real Difference
The short answer: “prefab” is an umbrella term for any home built in a factory, while “modular” and “manufactured” are two specific, legally distinct types of prefab. A modular home is built to the exact same state and local building code as a site-built house. A manufactured home is built to a separate federal HUD code on a permanent steel chassis. They look similar in a brochure, but they are treated very differently by appraisers, lenders, permit offices, and California ADU law.
The short version: Prefab = any factory-built home (the broad category). Modular = built to the same local/state code as a stick-built house, set on a permanent foundation, appraised like real estate. Manufactured = built to the federal HUD code on a permanent chassis, titled and valued more like a vehicle. Framework First builds modular, code-built homes in our Salinas factory. We are not a manufactured-home company, and that distinction matters for permits, financing, and resale.
Why the words matter
People use “prefab,” “modular,” and “manufactured” as if they all mean the same thing. They do not. The difference is not about quality or looks. It is about which building code the home is built to, and that single fact changes everything downstream: whether it qualifies as a real estate improvement, how it gets permitted as an ADU, how an appraiser values it, and which loans you can use to pay for it.
Get the category right and you avoid the most common and expensive mistake in this market: assuming a cheap-looking “manufactured” quote is the same product as a code-built modular home. It is not.
The three terms, defined plainly
Prefab (the umbrella)
“Prefabricated” simply means significant parts of the home are built in a factory rather than entirely on your lot. That is the whole definition. Modular homes are prefab. Manufactured homes are prefab. So are panelized kits and certain tiny homes. When someone says “prefab,” they have told you almost nothing specific yet. You still have to ask: built to what code?
Modular (built to local code, like a regular house)
A modular home is built in a factory in sections (called modules), trucked to your property, and set on a permanent foundation. The key fact: it is engineered and inspected to the same state and local building code as a home framed on-site. In California that means the California Building Code and CALGreen. There is no special “modular code.” A finished modular home is, legally and physically, the same animal as a site-built house. It just happened to be built indoors.
This is what Framework First builds. About 97% of each home is completed in our Salinas factory, then crane-delivered and set on a permanent foundation. Because it meets the same code as a stick-built home, it is appraised, financed, insured, and resold like any other real estate. We hold a contractor’s license (CSLB #1047146) and a manufacturer’s registration (MFG #1595931).
Manufactured (built to the federal HUD code on a chassis)
A manufactured home (the term that replaced “mobile home” in 1976) is built to a federal standard known as the HUD Code, not to your local building code. It is built on a permanent steel chassis (the frame with the axles), which is a defining feature. Even when the wheels are removed and it is set down on a lot, that chassis stays underneath. Because it follows a national code instead of local code, it is often titled and valued more like a vehicle than like real estate, and many California cities treat it differently for ADU and zoning purposes.
Manufactured homes can be a legitimate, affordable form of housing. But they are a different legal product, and confusing them with modular homes is where buyers get burned.
Side-by-side comparison
| Factor | Prefab (umbrella) | Modular (what we build) | Manufactured (HUD) |
|---|---|---|---|
| What it means | Any factory-built home | Built to local/state building code | Built to federal HUD code |
| Building code | Varies (it is a category) | Same as a site-built house (CA Building Code + CALGreen) | Federal HUD Code |
| Foundation | Depends on type | Permanent foundation, no chassis | Permanent steel chassis underneath |
| Appraised as | Depends on type | Real estate, like any house | Often closer to a vehicle/personal property |
| Typical financing | Depends on type | Standard mortgage, HELOC, construction/reno loans | Often chattel loans; fewer mortgage options |
| Resale & appreciation | Depends on type | Appreciates like a normal home | Can depreciate, especially if on a chassis/title |
| Qualifies as a CA ADU? | Depends on type | Yes, treated like site-built | Varies sharply by city |
Why Framework First builds modular, not manufactured
We chose code-built modular construction on purpose, because for a backyard ADU it gives you everything a site-built home gives you and almost nothing a manufactured home costs you in the long run:
- It is real estate. A modular ADU is appraised and valued like the rest of your property. That protects your resale value and appraisal. A home on a HUD chassis can be valued very differently.
- Financing is normal. Because it meets local code on a permanent foundation, you can use the same loan products homeowners already know. See our overview of how to finance an ADU in California.
- It permits like a house. California’s ministerial ADU process treats a code-built ADU the same as one framed on-site, with a 60-day decision on a complete application. Manufactured units can run into extra zoning and foundation requirements depending on the city.
- It is the same code, indoors. Building 97% of the home in a controlled factory means tighter tolerances, no weather delays, and consistent inspections, all to the same standard a stick-built home must meet. We walk through this in how an ADU is built.
The only thing that happens in a factory instead of your backyard is the construction. The rules the home is held to are identical.
What this means for your budget
Because we build modular, our pricing folds a permitting budget in alongside plans, foundation, the factory build, delivery, utility hookups, appliances, and final inspection. Our 14 models range from 405 to 1,200 square feet, with pricing from $180,000 to $557,000. Actual permit costs are set by your city and confirmed for your parcel in the feasibility study, so you know the real number before you sign, rather than hitting a “now add the foundation and the permits” surprise the way a cheap manufactured-home quote often does.
A few real examples from our lineup:
| Model | Size | Beds / Baths | All-inclusive price* |
|---|---|---|---|
| Four Fifty | 450 sq ft | Studio / 1 | $180,000 |
| Six Sixty | 660 sq ft | 1 / 1 | $287,000 |
| Nine Forty-Five 3/2 | 945 sq ft | 3 / 2 | $434,000 |
| Twelve Hundred U | 1,200 sq ft | 3 / 2 | $557,000 |
*Includes a permitting budget, not final permit costs. Permits and property-specific site work (septic, retaining walls, etc.) vary by property and are confirmed in your feasibility study.
Every model comes in one of three styles: Classic Craftsman (our standard), Urban Farmhouse, or Ultra Modern. For the full picture, see how much an ADU costs in California and browse the complete lineup on our models page.
Frequently asked questions
Is a modular home better quality than a manufactured home?
It is not exactly “better,” it is built to a different standard. A modular home meets the same local building code as a site-built house, so it is structurally and legally equivalent to a home framed on your lot. A manufactured home meets the federal HUD code on a permanent chassis. For an ADU that you want to appraise, finance, and resell like normal real estate, modular is the category you want.
Will a modular ADU appraise like a regular house?
Yes. Because it is built to the same code and set on a permanent foundation, an appraiser treats a modular ADU like any other improvement to your property. That is a key reason we build modular. You can read more in our guide to ADU appraisal and resale value.
Can I get a normal mortgage or HELOC for a modular ADU?
In most cases, yes. Modular homes qualify for the standard financing products homeowners already use, including HELOCs, cash-out refinances, and renovation or construction loans. Manufactured homes often rely on chattel (personal property) loans with different terms. Our financing overview covers your options at how to finance an ADU without cash.
Does California ADU law treat modular and manufactured the same?
Not always. State law makes the ADU approval process ministerial for code-built homes, with a 60-day decision on a complete application. A code-built modular ADU slots into that process cleanly. Manufactured (HUD-code) units can face additional city-by-city zoning and foundation requirements. The exact local rules vary, which is one of the things we confirm for you in the feasibility study.
Is Framework First a manufactured-home company?
No. We are a family-owned modular builder. We have built code-compliant homes since 2021, completing about 97% of each home in our Salinas factory, then crane-delivering and setting it on a permanent foundation built to the same California code as any site-built house.
Find out what fits your lot
The category your builder uses is one of the first things that shapes your permits, your financing, and your resale value. If you want a code-built modular ADU, the next step is simple: confirm what your specific property and city allow.
Our feasibility study reviews your lot, your zoning, and your local rules, then gives you a clear plan and price, permitting budget included, with no obligation. It is the fastest way to turn “prefab vs modular vs manufactured” from a confusing search into a concrete answer for your backyard.