ADU Fundamentals July 16, 2026 · 10 min read

Modular vs Manufactured vs Panelized vs Stick-Built ADU

Four ways to build an ADU, four different cost, timeline, financing, and permit profiles. Here is the honest comparison, with no method favored over another.

MR
AutoCAD & Chief Architect Certified

Lead Architectural Designer · Build With A Plan

Marcus has delivered 50+ permit-ready drawing sets for ADUs, garage conversions, and home additions across California, Texas, Arizona, Florida, and Oregon.

Modular vs Manufactured vs Panelized vs Stick-Built ADU

Four construction methods build an ADU: stick-built (framed on-site, board by board), modular (fully assembled in a factory, craned onto your foundation), panelized (wall and roof panels built off-site, assembled on your lot), and manufactured (built entirely to a federal code, delivered complete or near-complete). Each one changes your cost, your timeline, how a lender treats the loan, and what your city's building department actually reviews.

We design ADUs for all four methods, which means we have no reason to steer you toward the one that's easiest for us to sell. This guide lays out what each method actually costs, how long it actually takes, where financing gets complicated, and where permitting differs, so you can pick based on your lot and your timeline instead of whichever method a single builder happens to specialize in.

What Each Method Actually Means

The four terms get used loosely in casual conversation. Here's what separates them in practice, and it matters more for financing and permitting than most homeowners expect.

  • Stick-built. Framed on your lot, one board at a time, following the same sequence as a traditional house: foundation, then framing, then rough-ins, then finishes. Nothing arrives pre-assembled.
  • Modular. Built almost entirely inside a factory as one or more finished sections ("modules"), then transported and craned onto a foundation you or your builder prepared in advance. Built to the same state or local building code as a stick-built home.
  • Panelized. A middle path. Wall panels, roof trusses, and sometimes floor systems are built in a factory, then assembled on your foundation like a large kit. Interior finishes, MEP rough-in, and final work still happen on-site.
  • Manufactured. Built entirely to a single federal standard, the HUD Code, rather than your state or local building code. Historically called a "mobile home," though modern manufactured homes bear little resemblance to that image. Delivered complete or nearly complete and set on a foundation.
ADU design process comparing modular, manufactured, panelized, and stick-built construction methods

Cost Per Square Foot, Compared

Cost is where the four methods separate the most, and where the marketing gets the loosest. Here's an honest range for each, based on current national data rather than any single builder's price sheet.

Method
Cost Per Sq Ft (All-In) What Drives the Price
Find Out What Your Backyard Can Build

Free feasibility confirms your lot qualifies before you spend a dollar. If it qualifies, permit-ready drawings are 10 business days away. If it doesn't, you pay nothing.

Timeline: Factory Build vs. On-Site Sequence

Timeline differences come down to one variable: how much of the work happens in parallel versus in sequence.

Method
Typical Build Timeline Why
Financing Quirks by Method

This is the section that changes homeowners' minds most often, because it's the one least advertised by anyone selling a specific method.

  • Stick-built and panelized. Finance like any other on-site construction project: a construction loan, HELOC, cash-out refinance, or renovation loan (Fannie Mae HomeStyle, FHA 203(k)), converting to a standard mortgage once complete.
  • Modular. Once set on a permanent foundation, a modular ADU is real property, appraised the same way a site-built home is. It qualifies for the same conventional, FHA, and VA financing paths as stick-built, with no special lender workaround needed.
  • Manufactured. This is where financing gets genuinely different. Many lenders treat a manufactured home as personal property, not real estate, unless it's permanently affixed to a foundation and specifically titled as real property under your state's process. Depending on that classification, you may be limited to a chattel loan or an FHA Title I loan, both of which typically carry higher interest rates and shorter repayment terms than a conventional mortgage.

The practical takeaway: if you're financing through a HELOC or cash-out refinance against your primary home's equity, the construction method of the ADU itself matters less, since the loan is secured by the main house either way. If you're financing the ADU on its own, ask your lender directly how they classify a manufactured unit in your state before you commit to that method on cost alone.

ADU financing and permit paperwork comparison across construction methods

Permit and Code Differences

All four methods need a local building permit before anyone can legally live in the unit. What differs is which code governs the structure itself and how many parties sign off on it.