Both approaches produce a permanent, code-compliant ADU on a permanent foundation. What differs is where the building gets built, and the order the work happens in. Here is what each process actually looks like.
Neither is universally better. The right answer depends on your lot, your access, and how much you want to customize.
The building is constructed in sections inside a factory, trucked to your property, and set on a foundation with a crane. Final tie-in and finish work happen on site after the set.
The building is framed and finished entirely on your property, board by board, the way a traditional house is built. Every phase happens in sequence on site.
Both start the same way and end the same way. The middle is where they diverge.
Plans drawn, lot reviewed, finishes selected, town permits filed. Identical starting point for both methods.
Framed, wired, plumbed, sided and finished indoors on a production line, and inspected before it ships.
Foundation, utilities and access prepared at your property at the same time the building is in production.
Modules trucked in. Road width, turning room, grade and overhead lines all get checked well before this day.
Modules craned onto the foundation, joined, roof and siding tied together, utilities connected, final inspections.
Same starting point — plans, lot review, finish selections and town permitting before anything breaks ground.
Excavation, footings, walls poured and cured, utilities stubbed up. Nothing goes vertical until this is done.
Floor, walls, roof structure and sheathing built on site, adapted to real conditions as the work goes up.
Roofing, windows and doors, then siding and trim over housewrap. The building becomes weather-tight.
Rough-ins and insulation inspected, then drywall, trim, paint, flooring, fixtures and final inspections.
The real difference is overlap. With modular, the building is in production at the same time the foundation and utilities go in at your property — two phases running in parallel. Stick-built has to do them in order, because there is nothing to build on until the foundation cures. That overlap is where most of the schedule difference comes from, not from faster work.
General guidance. Every property changes the math, so treat this as a starting point rather than a rule.
| Factor | Modular | Stick-Built |
|---|---|---|
| Overall schedule | Often shorter, because factory production and site work overlap. | Longer in most cases, since every phase waits on the one before it. |
| Weather exposure | Minimal during the build. Materials stay dry indoors. | Real factor in New England. Rain and cold can stall framing and pours. |
| Site access | Critical. Needs road width, turning room, crane setup space, and clear overhead. | Flexible. Works on tight lots, steep grades, and hard-to-reach backyards. |
| Customization | Choose from the manufacturer's plans and options. Changes get locked in early. | Fully custom. Adjustments possible while the work is underway. |
| Cost predictability | More predictable. Much of the cost is fixed at the factory order. | More variable. Site conditions and change orders move the number. |
| Inspections | Factory inspected to state code, plus local inspections for foundation, utilities and final. | Local inspections at each phase — foundation, framing, rough-ins, insulation, final. |
| Best fit | Open lots with good access, homeowners who want a predictable schedule. | Difficult sites, unusual layouts, homeowners who want full design control. |
Process images on this page are representative illustrations, not photographs of completed ADU Visions projects.
Access, grade, utilities and setbacks usually answer this faster than preference does. A short conversation about your lot is normally enough to point you in the right direction.
Tell us where the property is and what you are picturing, and we will walk you through the realistic options.
(508) 257-1308
staff@aduvisions.com