What "prefab" actually means
A prefab (factory-built or modular) ADU is constructed in sections in a factory, trucked to your lot, and set on a prepared foundation. The factory part is real — climate-controlled precision, less weather delay. But everything around the box is site work: foundation, utility trenching and hookups, permits, and final assembly. See our prefab ADU page for the full picture.
Where prefab wins
Speed of the build phase. Factory and site work happen in parallel — foundation while the box is built — so on-site construction time shrinks.
Precision. Factory jigs beat field framing for square corners and tight envelopes.
Simple lots. Flat, open, easy-access lots let the truck and crane do their job without drama.
Where custom wins
Tricky lots. Slope, odd shapes, big trees worth keeping, narrow access — a factory box needs a crane path and a flat pad; custom framing adapts to the ground.
Design freedom. Match the main house's roofline, siding, and style exactly; lay out rooms for a specific person (an aging parent, a home office) rather than a catalog.
Maximizing the envelope. On a tight lot, custom design squeezes every allowed square foot out of the setbacks — see custom ADUs.
The permit myth, killed
Prefab changes how the box is built, not whether the county approves it. The ADU still needs health-department sign-off where it applies, the county ADU permit, the building permit, and inspections. Maryland's 90-day ministerial rule applies to the application either way. Factory certification may smooth the building-code review — it does not skip it.
Sources: Chapter 197 of the 2025 Laws of Maryland (HB 1466/SB 891), §4-505.
Cost: the honest shape
Prefab units are often quoted as a unit price — the box. The installed price adds transport, crane, foundation, utilities, permits, and site work, which can rival the box itself on a difficult lot. Custom builds quote the whole project. Compare installed-to-installed or you are comparing a steering wheel to a car. A note on prices: material costs move up and down, and no two lots need the same work. Treat any numbers on this page as starting points, not quotes.
The decision
Choose prefab for a straightforward lot, a need for speed, and a floor plan you like as drawn.
Choose custom for a tricky lot, a style worth matching, or a resident with specific needs.
We build custom — and we will tell you when prefab is the smarter buy for your land. That is what the free feasibility study is for.