Choosing a Modular, Prefab, or Tiny-Home Builder: What to Look For and Who to Trust
How to Tell Whether You Are Buying a Permittable California Home - or an Expensive Product With No Clear Path to Installation
The modular, prefab, and tiny-home market is full of beautiful websites, fast timelines, attractive prices, and promises that building a home can be simpler than traditional construction.
Sometimes it absolutely can be.
Factory construction can reduce weather exposure, improve repetition and quality control, shorten portions of the construction schedule, and make certain projects much more predictable.
But this part of the housing industry is also unusually easy for consumers to misunderstand because the words used in advertising do not always tell you what you are actually buying.
A “tiny home” might be a permanent dwelling built to the California Residential Code. It might be factory-built housing. It might be a manufactured home. It might be a park model or recreational vehicle intended for recreational or seasonal use. A “prefab” home might arrive nearly complete, or it might be a package of wall panels that still requires substantial site construction.
Before choosing the builder, figure out exactly what product they are selling and exactly how that product becomes a legal dwelling on your property.
First: Stop Using “Prefab” as if It Means One Thing
“Prefab” is a useful marketing word, but it is not one single California building classification.
Different products can travel through very different regulatory and construction paths. A project marketed as prefab might be:
Factory-built housing manufactured substantially off site and transported to a permanent installation location.
A manufactured home built under the federal HUD manufactured-housing standards.
Panelized or component construction where walls, floors, roof systems, or other components are fabricated off site and assembled into a site-built structure.
A modular system composed of large completed sections.
A tiny home constructed as a permanent code-compliant dwelling.
A tiny home on wheels, park model, or recreational vehicle.
Those distinctions affect permitting, inspections, installation, financing, foundations, utilities, resale, and whether the product can legally be used the way you intend.
Do not ask only, “Is this prefab?” Ask, “What is this legally?”
Factory-Built Housing Is Still a Real House
California HCD defines factory-built housing as a factory-constructed version of a site-built residential building that is manufactured and transported to its permanent installation location.
The design and factory construction are reviewed through the state factory-built housing system. HCD-certified third-party agencies can perform design approval and quality-assurance functions, and approved units receive an HCD insignia.
But that state-level factory approval does not eliminate the local project.
The local building department still has authority over installation and site-related work. The approved factory plans must be provided to the local agency, and the installation is subject to local inspection.
That distinction is critical:
The factory can be approved while your property, foundation, utilities, grading, access, and installation still require local approval.
“HCD Approved” Does Not Mean “Your Permit Is Approved”
This may be the single most important sentence in this article.
A seller may truthfully tell you that a unit, plan, system, or manufacturing process has state approval.
That does not necessarily mean your city or county has approved that house on your parcel.
Your project may still require some combination of:
Planning or zoning review.
A site plan.
A foundation plan.
Site-specific structural engineering.
Grading and drainage plans.
Utility plans and connections.
Sewer or septic approval.
Well review.
Fire access or fire-flow compliance.
Title 24 or other energy documentation, depending on the product and approval path.
Floodplain compliance.
Local building permits and inspections.
When a company says “approved,” ask the next question:
Approved by whom, for what, and what approvals are still required on my property?
“Preapproved” Needs the Same Follow-Up Question
Preapproved plans can be extremely useful.
But “preapproved” does not mean the same thing as “you can put this anywhere.”
A plan might be preapproved by one city, accepted through a particular program, approved through an HCD factory-built housing process, or engineered as a repeatable standard design.
The site still exists.
The property still has setbacks, utilities, soils, access, fire conditions, flood conditions, and possibly septic, well, grading, environmental, or other constraints.
Ask the builder to identify the exact approval they are relying on and show you the documentation.
If they say the model has already been permitted in California, ask where.
If they say it has been permitted in your jurisdiction, ask for the permit number or project address if the owner has authorized them to share it.
“We have done these in California” is useful. “Here are three completed permitted projects” is much more useful.
Tiny Homes Require Extra Caution
“Tiny home” describes size and style more than it describes the legal status of the structure.
A small permanent dwelling can be perfectly legitimate housing.
But a tiny home on wheels may fall into a completely different category.
California HCD distinguishes permanent housing from recreational vehicles. Park trailers or park models are recreational vehicles designed for recreational or seasonal use, and HCD guidance states that recreational vehicles are not intended for occupancy as permanent dwellings unless a lawful local or park framework allows the use.
That means a beautiful 399-square-foot unit with a kitchen, bathroom, loft, and wheels is not automatically a legal permanent ADU simply because the seller calls it a “tiny home.”
Before buying, determine whether the product is intended and certified as:
Permanent residential construction.
Factory-built housing.
A manufactured home.
A park model or park trailer.
Another recreational vehicle classification.
Then confirm that your jurisdiction allows that specific product for your intended use.
Do this before you pay for it.
An ADU Is a Use - Not a Brand of Building
An ADU is a legal dwelling use on a parcel. It can be created through several construction methods.
A factory-built home, manufactured home, panelized building, modular system, or conventional site-built structure may potentially serve as an ADU if it meets the applicable legal and building requirements.
California HCD specifically recognizes a manufactured home within the statutory definition of an ADU.
But a company putting “ADU” in the product name does not make the unit a permitted ADU.
The property and the product both have to qualify.
“ADU model” is marketing. “Permitted ADU on this parcel” is a land-use and building approval.
The Advertised Price Is Usually Not the Project Price
This is where many buyers get surprised.
A company may advertise a beautiful unit for $89,000, $129,000, or $199,000.
That number may be perfectly accurate for the product being sold.
It may still be nowhere near the cost of having a legal, occupied home on your property.
Find out whether the advertised price includes:
Design and engineering.
Permitting assistance.
Local permit fees.
Foundation.
Excavation and grading.
Drainage.
Transportation.
Oversize-load permits.
Crane or setting costs.
On-site assembly.
Roof or exterior marriage-line completion.
Interior marriage-line completion.
Utility trenching.
Water connection.
Sewer connection or septic work.
Electrical service and connection.
Gas or propane work.
Fire sprinklers if required.
Driveway or fire-access improvements.
Decks, stairs, landings, and accessibility features.
Appliances.
Finish upgrades.
Sales or use taxes where applicable.
Cleanup and final inspection work.
You need two numbers:
What does the house cost?
and
What does it cost to have a legal, finished, occupiable house on my property?
Those are not necessarily the same number.
Find the Missing Scope
Modular and prefab projects often involve more than one company.
The manufacturer may build the unit.
A transporter may deliver it.
A crane company may set it.
A foundation contractor may prepare the site.
A local general contractor may complete connections and finishes.
A separate engineer may design the foundation.
A permit consultant or designer may handle the local permit package.
That arrangement can work extremely well.
But someone needs to own every piece of the scope.
Before signing, create a responsibility list:
Who obtains the local permit?
Who provides the site plan?
Who designs the foundation?
Who confirms the unit and foundation drawings coordinate?
Who handles Title 24 or energy documentation if required?
Who handles grading and drainage?
Who handles sewer or septic?
Who handles water?
Who handles electrical service?
Who coordinates fire requirements?
Who transports the unit?
Who is responsible if transportation damages it?
Who provides the crane?
Who sets and anchors the building?
Who makes the final weatherproof connections?
Who completes interior connections?
Who schedules local inspections?
Who corrects inspection failures?
Who obtains final occupancy approval?
If the answer to an important item is “the owner handles that,” make sure you understand what “handles that” actually means.
Ask Who Is Responsible When the Factory Meets the Site
The most dangerous gap in a modular project can be the line between factory scope and site scope.
The factory says the foundation is wrong.
The foundation contractor says the module dimensions changed.
The installer says the plans did not show a connection.
The local inspector says the field condition does not match the approved documents.
And suddenly everyone is pointing at someone else.
Before ordering, ask:
Who verifies the foundation dimensions before fabrication?
Who confirms utility stub locations?
Who checks finished floor elevation?
Who confirms anchor and connection details?
Who coordinates plan revisions between factory and local drawings?
Who pays if the unit arrives and cannot be set because the site work is wrong?
Who pays if the factory dimensions do not match the approved site work?
You want a clear chain of responsibility before the truck arrives.
Ask to See the Actual Approval Documents
Do not rely entirely on sales language.
For factory-built housing, ask to see documentation showing the applicable design approval and how the HCD insignia process works for the unit you are purchasing.
Ask which HCD-certified Design Approval Agency or Quality Assurance Agency is involved if a third-party agency is being used.
Ask whether the plan approval is current.
This matters especially in 2026 because California moved to the 2025 Building Standards Code for new permit applications beginning January 1, 2026, and HCD states that new factory-built housing plans and designs entering production under the new cycle must comply with the applicable 2025 standards. HCD also notes that approved factory-built housing plans generally remain valid for 36 months from approval.
If a salesperson cannot explain what approval applies to the product, ask to speak with the technical or permitting person who can.
Do Not Buy From Renderings Alone
A rendering proves that someone can create a rendering.
It does not prove that the model has been engineered, manufactured, transported, installed, permitted, occupied, or lived in.
Ask to see:
Completed units.
Units under construction in the factory.
Completed installations in California.
A project similar in size to yours.
Interior photographs that are not renderings.
Foundation and setting photographs.
A completed project after a year or more of occupancy, if available.
If every image is a pristine computer rendering and the company cannot identify a completed installation, understand that you may be an early customer for that design.
That is not automatically bad.
But it is different risk.
Talk to Customers Who Made It All the Way to Occupancy
A customer who placed an order three months ago can tell you whether the sales process was pleasant.
A customer who has lived in the home for a year can tell you much more.
Ask former customers:
Was the final project close to the original total budget?
How accurate was the delivery schedule?
Did permitting go the way the company represented it?
Who handled local corrections?
Were there factory defects?
How quickly were warranty items addressed?
Were transportation or crane costs as expected?
Did the site contractor and manufacturer coordinate well?
Were there surprise scope gaps?
Would you buy from the company again?
The most valuable reference may be the customer who had a problem and can tell you how the company responded.
Ask What Happens if the Company Fails
This is uncomfortable and important.
Prefab construction can require significant payments before the finished house exists on your land.
Ask:
When do payments become nonrefundable?
Are deposits held separately or immediately used by the company?
When does title to materials or the unit transfer?
What happens to work in progress if the manufacturer closes?
Is there any payment or performance protection?
Can partially completed components be released to you?
What happens if financing is delayed?
What happens if your permit is denied or significantly delayed?
The answers will vary by business model.
You are not looking for one magic contract structure.
You are trying to understand how much of your money is exposed at each stage and what you receive in exchange for it.
Do Not Order the House Before You Understand the Site
This is where I would be especially cautious.
A company wants to sell houses.
Your property may have:
A septic limitation.
A marginal well.
A difficult driveway.
A floodplain.
A floodway.
A creek setback.
A wildfire access issue.
A grading problem.
An easement through the building area.
A utility problem.
A zoning or ADU issue.
An archaeological, biological, or other environmental constraint.
The house may be perfectly legal and beautifully built and still be the wrong house for that site.
Site feasibility should come before a large nonrefundable factory order.
Transportation Is Part of the Design
A house that can be built in a factory still has to reach your property.
For large modules, investigate:
Road width.
Turning radius.
Bridge limits.
Overhead wires.
Tree clearance.
Gate width.
Driveway grade.
Staging area.
Crane access.
Distance from the crane to the foundation.
Seasonal road conditions.
Oversize transportation restrictions.
A rural parcel can have an excellent building site that is extremely difficult to reach with a large module.
That does not necessarily mean prefab is impossible.
It may mean a panelized system, smaller modules, or another construction method makes more sense.
The best building system is the one that works with the property.
Understand the Difference Between Modular and Panelized
Large volumetric modules can arrive with much of the interior complete.
Panelized systems may arrive as wall, floor, and roof assemblies and require considerably more on-site construction.
Neither is inherently better.
They solve different problems.
Volumetric modular construction may reduce on-site finish time but creates greater transportation and crane considerations.
Panelized construction can be easier to deliver to difficult sites and may offer more flexibility, but the amount of local labor required can be much closer to conventional construction than buyers expect.
Ask the company:
What percentage of this house is actually complete when it arrives, and what remains to be built on site?
Warranties Are Only as Useful as the Person Who Shows Up
A ten-year warranty sounds wonderful.
Now ask who will perform the repair.
If the factory is 900 miles away and the local installer says factory defects are not their responsibility, the warranty process matters enormously.
Ask:
Who receives warranty claims?
Who determines whether the issue is factory or installation related?
Are there local service technicians?
Who pays travel costs?
How quickly are emergency water-intrusion or electrical issues addressed?
Are windows, cabinets, fixtures, roofing, siding, and mechanical equipment standard products that can be serviced locally?
Are replacement components proprietary?
Does altering the home after installation affect the warranty?
HCD notes that alterations to factory-built housing before installation require state-level approval, while post-installation alterations fall under the local building department. That is another reason to understand how future changes will be handled.
Financing and Appraisal Need to Be Checked Early
Do not assume every lender treats every construction system the same way.
The legal classification of the home, the land ownership, foundation, title, construction contract, draw schedule, and appraisal process can affect financing.
Before making a large deposit, tell the lender exactly what you are buying.
Provide the manufacturer, construction type, plans, contract structure, site-work scope, and installation method.
Ask whether the lender has financed this type of project before.
The same applies to your insurance company and, when relevant, your appraiser.
A house can be perfectly buildable and still be difficult to finance under the loan product you planned to use.
Be Careful With “Turnkey”
“Turnkey” should be one of the most specific words in the contract, not one of the vaguest words on the website.
If a company advertises turnkey, ask whether that means:
The unit leaves the factory complete.
The unit is delivered to your property.
The unit is set on the foundation.
Utilities are connected.
Site work is complete.
Local permits are included.
Final inspection is passed.
A certificate of occupancy or equivalent final approval has been obtained.
You can literally receive the keys and legally move in.
If their definition of turnkey ends when the truck unloads the building, you need to know that before comparing their price with another company.
Who Can You Trust?
The same principle from choosing a licensed contractor applies here, but there are more moving pieces.
Look for consistency between what the company says and what you can verify.
The product classification matches the approval documents.
The advertised model matches something they have actually built.
The claimed California experience matches completed California projects.
The quoted price matches a clearly defined scope.
The permitting claims match what the local jurisdiction says.
The payment schedule matches meaningful manufacturing milestones.
The warranty has a real service process.
The company can clearly explain who owns every part of the project.
A trustworthy company should not be threatened by detailed questions.
They should already know the answers to most of them.
And when they do not know, they should be willing to find out instead of making something up.
Red Flags I Would Take Seriously
Calling a park model or RV a universally legal permanent ADU.
Claiming “HCD approved” means no local permit is required.
Claiming a plan is “preapproved everywhere in California.”
Refusing to identify the legal classification of the product.
No completed projects that can be verified.
Only renderings and no real construction photographs.
A price that excludes most site work but is advertised as the total ADU cost.
Large nonrefundable payments before site feasibility is established.
No clear answer about who handles the foundation or local permit.
No coordination process between factory drawings and site drawings.
No clear warranty service in your region.
Pressuring you to order before speaking with your local jurisdiction.
Telling you zoning, septic, fire, flood, or access “won’t be a problem” without reviewing the property.
Refusing to provide approval documentation.
Vague answers about transportation and crane costs.
No clear plan for corrections if the local inspector rejects part of the installation.
The issue is rarely one imperfect answer.
It is a pattern of selling certainty where there is actually unresolved responsibility.
Green Flags
They immediately explain exactly what type of construction they sell.
They distinguish factory approval from local site approval.
They provide actual approval documents.
They have completed California installations.
They encourage site feasibility before ordering.
They clearly separate factory price from installed project cost.
They provide a detailed responsibility matrix.
They coordinate directly with the local designer, engineer, contractor, or permit consultant.
They can explain transportation and setting requirements.
They identify what is excluded.
They have a clear process for warranty work.
They can provide customers who have reached final occupancy.
They do not pretend every property is suitable for their system.
One of the best signs is a company willing to tell you their product is not the right product for a particular site.
Before You Order: My Checklist
Before making a substantial payment to a modular, prefab, or tiny-home company, I would want answers to these questions:
What is the exact legal classification of the unit?
What building standard is it constructed under?
What HCD, HUD, third-party, or local approvals apply?
Can I see the approval documentation?
Is the approval current for the 2026 code cycle or otherwise still valid?
Can this specific product legally be used as an SFR or ADU on my property?
Has the local jurisdiction confirmed the permitting path?
Has the site been evaluated for zoning, setbacks, access, utilities, fire, flood, septic/well, grading, and other constraints?
What exactly is included in the advertised price?
What is excluded?
What is the realistic installed project budget?
Who designs and builds the foundation?
Who handles local permits?
Who coordinates factory and site plans?
Who transports and sets the unit?
Who is responsible for damage during transportation or setting?
Who connects utilities?
Who handles local inspection corrections?
Who obtains final occupancy approval?
What payments are required and when do they become nonrefundable?
What happens if the permit is delayed or denied?
What happens if the manufacturer fails before delivery?
Who performs warranty repairs locally?
Can I speak with customers who have completed installation and moved in?
Has my lender confirmed it will finance this exact construction method and contract structure?
If the company cannot answer these questions, you are not ready to order the house.
The Bottom Line
Modular, prefab, panelized, manufactured, and tiny-home construction can be excellent tools.
They can make housing faster, more repeatable, and sometimes more affordable.
But the product is only one part of the project.
You are choosing:
A building system.
A manufacturer.
An approval pathway.
A transportation strategy.
A foundation.
A site contractor or installer.
A permitting process.
A warranty relationship.
A chain of responsibility.
The house shown on the website is the easy part to understand.
The real work is figuring out how that house becomes your legal, finished, occupiable home on your specific California property.
Do not buy the rendering. Buy the complete path from factory to final inspection.
Looking Ahead
Next: How to Read a Contractor or Prefab Bid Without Getting Burned.
We will look at how to compare bids when one company is pricing conventional construction, another is selling a factory-built unit, and a third is advertising a “turnkey” package - including allowances, exclusions, site work, transportation, utility costs, change orders, and the missing scope that can make the cheapest proposal the most expensive project.
If you are considering a modular, prefab, manufactured, panelized, or tiny-home project in California, Buchanan Land Use Consulting can help evaluate the property and permitting path before you commit to a building system or make a large nonrefundable order.
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