Panelized vs. Modular vs. Stick-Built ADU Construction: What Actually Differs

Accessory dwelling unit permitting has grown sharply in recent years, and a large share of that growth is factory-built construction rather than conventional site-built framing. But "factory-built" isn't one method — it covers at least three approaches that get marketed almost interchangeably: panelized, modular, and stick-built. If you're evaluating an ADU program, the difference matters more than the marketing suggests.

Stick-built: the baseline

Conventional wood or light-gauge steel framing, assembled entirely on site. Every wall, floor and roof member is cut, fastened and finished in place. It's the most flexible method for one-off custom designs, and it's what most local trades already know — but it also carries the most schedule exposure: weather delays, sequential trade scheduling, and site labor availability all sit directly on the critical path.

Modular: complete rooms, shipped whole

Modular construction fabricates finished, code-inspected room modules — often with drywall, flooring, and fixtures already installed — inside a factory, then ships them by truck or crane to the site for connection. This compresses field time significantly and moves most of the labor indoors. The trade-off is transport: modules are large, road-width-constrained, and need crane access and a set staging plan. Design flexibility is also narrower, since modules are built around standard shippable dimensions.

Panelized: flat panels, assembled on site

Panelized systems — like PanLbilt's steel-frame, fiber-cement and foam-cement panels — fabricate flat structural panels off-site to an approved drawing set, then ship them flat for crane-set field assembly. This keeps the transport and staging footprint smaller than modular (flat panels stack more efficiently than finished room boxes), while still moving the bulk of fabrication into a controlled factory process rather than open-site framing.

Because the panels are structural components rather than finished rooms, panelized systems can also flex more on layout and elevation than modular, while still cutting the field-assembly window well below a conventional framing sequence. PanLbilt's own demonstrated example: a 2,475 SF two-story shell enclosed in four days of on-site assembly.

Comparing the three

Which one fits your project?

Stick-built still makes sense for highly custom, one-off designs where no repeatable plan exists. Modular tends to win when site access and crane logistics are straightforward and a standard room layout works. Panelized is strongest where a project needs more design flexibility than modular allows, but still needs to compress the enclosure schedule and reduce on-site trade sequencing — which is why it shows up often in ADU and infill programs and repeatable residential builds.