How to vet a modular manufacturer: a buyer's checklist

Picking a modular manufacturer is closer to picking a long-term supplier than hiring a subcontractor. Your building will be produced inside their plant, on their schedule, under their quality system. A good fit can save months. A poor one can stall the whole project. This checklist covers what to verify before you sign.

1. State approvals for your project's location

Most states that regulate modular buildings run a program that approves plans and monitors production for buildings shipped into that state. The Modular Building Institute keeps a list of state program administrators and contacts. Ask the manufacturer which states they are currently approved in and how long it takes them to get approval in a new one.

In California, for example, factory-built housing needs plan approval from an HCD-certified design approval agency, in-plant inspection by an HCD-certified quality assurance agency, and an HCD insignia of approval before it ships. In Texas, industrialized buildings are inspected in the plant by approved third-party inspection agencies, and inspections may be unannounced. A manufacturer that already works under a program like these knows the routine.

2. Third-party inspection agency

Ask who their third-party inspector is, how often that agency is in the plant, and whether you can see recent inspection reports. A manufacturer that hesitates here is telling you something.

3. Project experience that matches yours

Don't settle for "we've built hundreds of buildings." Ask for projects that match yours in use, height, construction type and size. A plant that builds excellent single-story classrooms may never have built a four-story wood-frame apartment building. Ask for addresses and owner contacts, and call them.

Questions for those references:

• Did modules arrive on the dates promised?
• How many punch-list items came from the factory versus the site?
• How did the manufacturer handle a problem when one came up?
• Would you use them again for the same building type?

4. Capacity and the production slot

Plants schedule production months ahead. Ask:

• What is your current backlog, and when is the earliest realistic start?
• How many modules or panels do you produce per week on a project like mine?
• What happens to my slot if my permits or site are late?
• Do you store finished modules, and what does that cost?

5. Visit the plant

Walk the line in person if you can. Look at how material is stored, whether work areas are clean and organized, how modules are protected before shipping, and whether quality checkpoints are posted and in use. Ask to see a module at the stage your project would reach before shipping.

6. Engineering and design responsibility

Get clear answers on who engineers the modules, who engineers module-to-module and module-to-foundation connections, and who stamps what. The ICC/MBI 1200 standard spells out roles for the architect, modular manufacturer, construction manager and general contractor. Use it as a reference when you write the contract so nothing falls between parties.

7. Scope boundaries

The most common modular disputes are about who does what at the joints. Get a written split of responsibility for:

• Foundations and anchoring
• Transport and permits
• Crane and setting crew
• Weather protection during and after set
• Marriage lines, fire-stopping and finish work at module joints
• Utility hookups between modules and to the site
• Final inspections and certificate of occupancy

8. Financial health

Ask for references from the manufacturer's material suppliers and lenders, and ask how they handle deposits. Many plants require deposits to buy materials. Understand what protects your money if the plant runs into trouble, and consider escrow or payment tied to production milestones you can verify.

9. Warranty and service after set

Find out what the factory warranty covers, how long it lasts, who responds to callbacks, and whether that changes when the setting crew and GC are different companies.

10. Fit with your market

According to MBI, most U.S. permanent modular work is in multifamily, commercial and education. If your project is in one of those segments, you should have several qualified plants to compare. If not, widen your search and spend more time on step 3.

A short version for the first call

If you only have ten minutes with a manufacturer, ask three things: which states they are currently approved in, which recent project is most like yours, and what their earliest production slot is. The answers will tell you whether a second call is worth it.

Warning signs

Some answers should slow you down:

• They can't name the inspection agency that works in their plant.
• They have no recent projects close to yours in type and size.
• They won't let you visit the plant or talk to past owners.
• They push for a large deposit with no link to production milestones.
• Their quote is far below the others and they can't explain why.
• They are vague about who designs and stamps the connections.

None of these alone means a plant is a bad choice, but each deserves a direct question and a written answer.