Prefabricated Wall Panels That Arrive Finished: What's Inside a Flat-Pack Panel

A finished MBS wall panel leaves the factory with the windows, doors, cladding, insulation, sheathing, and MEP already installed. It is not a frame. It is a wall, complete, ready to be set and connected.

That is the whole argument for advanced panelized construction. It is also the part most developers have never seen.

Offsite methods still account for just 3% of U.S. single-family home completions, according to NAHB analysis of Census Bureau Survey of Construction data. Interest in the category is high. Familiarity is low. So here is exactly what a prefabricated wall panel is, what is inside one when it leaves our 40,000 ft2 CNC manufacturing facility, and what that changes on your schedule.

What is a prefabricated wall panel?

A prefabricated wall panel is a complete section of wall built in a factory and shipped to the job site as one unit. The frame is cut by CNC machine to engineered tolerances. Everything that can be installed indoors is installed indoors, on a flat, level table, under controlled conditions.

Panelized construction builds a building in flat pieces. Modular construction builds it in finished three-dimensional boxes. Stick-built construction builds it, board by board, outdoors, in the weather. Panels give you factory quality without the freight cost and site constraints that come with shipping finished boxes. Our FAQ covers the method comparison in more detail.

Open panel vs closed panel construction

The industry grades panels by how much work is already done when the truck arrives.

• Open panel. Frame and sheathing only. Insulation, membranes, wiring, plumbing, windows, and finishes all still happen on site.

• Closed panel. Insulation, sheathing, and membranes are installed in the factory. Service voids and conduit runs are built in. Window and door openings are formed and often glazed before shipping.

MBS builds at the finished end of the closed panel range. Windows, doors, cladding, insulation, sheathing, and MEP are all pre-installed before a panel leaves the floor. The site crew sets the wall and makes the connections. See how the process runs from design to assembly on our services page.

What is inside an MBS panel when it ships

• CNC-cut structural frame. Cut to engineered tolerances by machine, not measured and cut in a muddy yard.

• Sheathing. Applied and fastened flat, so the panel is square and stays square.

• Insulation. Installed indoors with consistent fill and no weather exposure before close-in.

• Windows. Glazed, set, and sealed into the opening before the panel is loaded.

• Doors. Hung in the opening, square, and ready to trim.

• Exterior cladding. Applied to the panel face, so the building envelope arrives finished rather than scheduled.

• MEP. Conduit, boxes, and plumbing runs are installed in the panel, so electricians and plumbers connect instead of rough in.

Why factory finishing changes the schedule

MBS manufactures a 1,500 ft2 home in one week. On site, that same home reaches weather-tight lockdown in 4 days.

The reason is sequencing. On a stick-built site, trades work in series. Framing waits on the slab. Sheathing waits on framing. Windows wait on sheathing. Insulation waits on windows. Every one of those steps also waits on the weather.

In a factory, those steps run in parallel across stations under one roof, on a fixed schedule, indoors. Rain does not stop a station. A late trade does not idle the whole job. That is how panelized construction delivers up to 30% lower project cost, 50% faster delivery, and up to 90% less waste. Our solutions page breaks down where each of those savings comes from.

How finished panels ship

Panels ship flat-packed and vertically on standard flatbeds. No oversize loads. No escort vehicles. No craning a finished box down a narrow residential street.

MBS ships within 1,000 miles of our St. Louis facility, which covers most of the eastern half of the country. Panels arrive in installation sequence, so the crew unloads and sets in order rather than staging, sorting, and double-handling material on a tight site.

What this means for developers, GCs, and municipalities

• Cost certainty. Panels are priced at the factory before the first truck moves. Fixed factory pricing removes most of the change-order exposure that lives in field labor.

• A smaller site crew. Most of the labor happens in the plant. The site team is smaller, the work is safer, and the schedule depends on fewer subcontractors showing up.

• A lockdown date you can plan around. Weather-tight in 4 days means interior trades start on a date you can commit to in a pro forma.

• Repeatable quality. The hundredth panel is built the same way as the first. That matters most on multi-unit and scattered-site affordable housing.

The same finished-panel system builds single-family homes, ADUs, tiny homes, townhomes, mixed-use buildings, temporary and disaster-relief structures, and high-density multi-residential projects from one to six stories. See the full range on our products page.

Frequently asked questions

What is the difference between open panel and closed panel construction?

Open panel wall panels arrive as frame and sheathing only, so insulation, services, and windows are installed on site. Closed panel wall panels arrive with insulation, sheathing, and service runs already installed in the factory. MBS panels go further and arrive with windows, doors, cladding, insulation, sheathing, and MEP pre-installed.

Do prefabricated wall panels come with windows already installed?

MBS panels do. Windows are glazed, set, and sealed into the opening at the factory, along with doors and exterior cladding. That is what lets a 1,500 ft2 home reach weather-tight lockdown on site in 4 days.

Are prefabricated wall panels code compliant?

Yes. Panelized construction is a manufacturing method, not a separate code path. Panels are engineered and built to the building code that applies at the project site, and the finished building is inspected like any other construction.

How far can panelized wall panels be shipped?

MBS ships flat-packed panels within 1,000 miles of its St. Louis, Missouri facility on standard flatbeds. Panels load vertically and flat-packed, so a standard trailer carries a full load without an oversize permits.

How much construction waste does panelized construction avoid?

Up to 90% less waste than conventional site building. Factory cutting is optimized across the whole project, offcuts are captured and reused, and material does not sit outside, exposed to the weather.

Build with panels that arrive finished.

Module Building Systems is an advanced panelized construction manufacturer at 921 N 20th Street, St. Louis, MO 63106, founded in 2023. We build finished wall and floor panels for developers, general contractors, non-profit developers, municipalities, and states. Learn more about MBS.

Tell us about your project, and we will price it. Get a quote or email info@modulebs.com.